Agroclimatology

Mohammad Mohaiminul Islam MS 2018, GES, CU mmohaiminul@yahoo.com
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AGROCLIMATOLOGY
According to Encyclopedia of World Climatology (2005), Agroclimatology is a field in the
interdisciplinary science of agrometeorology, in which principles of climatology are applied to
agricultural systems.
Agroclimatology is an interdisciplinary science dealing with the application of fields of
meteorology and climatology to biological and agricultural systems (Hoppe, 2000).
Aim of Agroclimatology
According to WMO (1981),
(1) Strategic decisions in long-range planning
(2) Tactical decisions in short-term planning
(3) Agrometeorological forecasts
Other-
(4) To study climatic resources of a given area for effective crop planning.
(5) To evolve climate based effective farm operations.
(6) To study crop weather relationships in all important crops and forecast crop yields based on.
Scope of Agroclimatology
1. What crop should I plant?
2. When should I plant?
3. What hybrid should I plant?
4. What is happening with the crop in the other parts of the world?
5. What seeding density should I choose?
6. What is the optimum fertilizer treatment?
7. Is irrigation an effective option?
8. Can I grow a second crop?
9. What is the optimal location for new crop?
10. Is the duration of growing season changing?

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11. Is the likelihood of heat stress changing?
12. Is irrigation cost effective?
Perspective/Approach of Agroclimatology
The perspective of agroclimatology can be defined with a holistic view and approaches of
agroclimatology.
1. The holistic science
2. The approaches
The holistic science: Agroclimatology is an interdisciplinary science in which the main scientific
disciplines involved are atmospheric sciences and soil sciences, which are concerned with the
physical environment, and plant sciences and animal sciences (including their pathology,
entomology, and parasitology, etc.), which deal with the contents of the biosphere and it has an
emphasize on climate or long term weather.
The Approaches: According to Mavi & Tupper (2004)-
Approach one: An agroclimatologist first formulates an accurate description of the
physical environment and biological responses.
Approach two: At the second stage, he or she interprets biological responses in terms of
the physical environment.
Approach three: Third, he or she makes agroclimatological forecasts.
Approach four: The final goal is to develop agroclimatological services, strategies, and
support systems for on-farm strategic and tactical decisions and to implement them in
collaboration with specialists in agriculture, livestock, and forestry.
Application of Agroclimatology
It has two types of applications-

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1. Strategic: The strategic role is involved in the assessment of long-term utilization of
natural resources in the development of crop diversity.
2. Tactical: The tactical role is more concerned with the short-term and field-scale decisions
that directly influence crop growth and development.
Under these two categories, the major applications of agroclimatology are as the following sectors-
1. Solar radiation, weather and climate elements and their role on agriculture
2. Environmental temperature and crop production relationship
3. Climatological methods for managing farm water resources
4. Drought monitoring and planning for mitigation
5. Interaction among climate, crop pests, and parasites of animals
6. Remote-sensing applications in agroclimatology
7. Role of computer models in managing agricultural systems
8. Agroclimatological services and their management
9. Using climate information to improve agricultural systems
10. Assessing the climate change and its impact on agriculture
Chronology of Development of Agroclimatology
Attempts to relate agricultural production to weather go back at least 2,000 years and are still
evolving. The twentieth century can be termed a very progressive and fertile one in respect to
meteorology and agroclimatology (Fleming, 1996). Qualitative studies in the nineteenth century
were followed by statistical analyses, then by microclimatic measurements, and most recently by
modeling (Decker, 1994; Monteith, 2000).
Quantification of Crop-Weather Relationships
Visual observations of the microclimate and its impact on crop plants have been going on for
several centuries. However, measurement of the characteristics of the microclimate in laboratory
and experimental fields was strengthened during the first half of the twentieth century. The role of
water in soil climate was recognized, and the link between the physical properties of soil, heat

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exchange, and water movement was investigated. It is well recognized that year-to-year variations
in yields and regional commodity production are associated with variations in climate. Efforts were
made to describe this relationship through statistical analysis of the correlation of yields with
monthly rainfall. These analyses were a first attempt to use statistics to describe the nature of the
relationship between variable yields, production, and climate. Later, the relationship between
yields and rainfall was studied using multiple correlation methods. Since the 1920s (with some
refinements in techniques), correlation and regression analyses have become the favorite tools for
describing yield-weather relations.
Energy Balance Quantification
The first half of the twentieth century saw great contributions toward the quantification of water
loss and use by plants. Research studies on the measurement and analysis of energy fluxes above
crops and on crop evapotranspiration were stimulated. It was in this period that Bowen proposed
a method (Bowen ratio) of partitioning the energy used in evaporation and heating the air. Penman
published a rational method for using meteorological observations to estimate evaporation from a
free water surface and vaporization from a plant canopy. The Penman method for estimating
evapotranspiration has become a standard tool for estimating the need for irrigation water by
agricultural engineers, agronomists, and meteorologists throughout the world. At the same time,
the Thornthwaite method for estimating potential evapotranspiration was published. Further
research into the energy balance resulted in the development of the eddy correlation method for
estimating latent and sensible heat transfer. Later, Blaney and Criddle developed the consumptive
use principle for irrigation scheduling. This technique has been widely used by agriculturists in
the semiarid regions of the world. In more recent years, advanced and reliable instrumentation has
made possible continuous measurements of biometeorological exchange processes, such as
measurements of mass and energy exchange to assess the plant community’s response to
atmospheric variables.

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Biological Studies in Controlled Climates
By the middle of the twentieth century, technology was available to build facilities in which
biological responses to environmental conditions could be measured quantitatively. These
facilities provided a way to study the responses of plants and animals to diurnal variations in
weather conditions. One such facility was at the California Institute of Technology. At about the
same time, a large animal facility at the University of Missouri, called the Missouri Climatic
Laboratory, was established for studies dealing with the physiological response and production of
dairy cattle to variations in temperature, humidity, wind, and radiation loads. As a result of these
facilities, several excellent studies have contributed to a better understanding of climate and
weather effects on plants and animals. These two laboratories served as precursors to the
development of the growth chambers used today in nearly every part of the world.
Modeling Biological Response to Climate
By the late 1960s and early 1970s, an extensive literature was available that documented the
response of plant growth and development to environmental conditions. This information paved
the way for work on mathematical models of plant response and yields to varying environmental
conditions. The comprehensive development and use of plant and animal dynamic simulation
models started with the availability of computers in the early 1970s. By the close of the twentieth
century, several thousand computer-based plant and animal dynamic simulation models had been
developed to expand scientific insights into complex biological and environmental systems, and
their use has resulted in huge economic benefits. The application of crop simulation models and
simulation-based decision support systems became more acceptable to the agricultural community
during the final decade of the twentieth century (Hoogenboom, 2000). Increases in the
sophistication of computers and decreased costs are further fueling rapid advances in modeling.
Interest has arisen in the topic of scaling from the leaf level to the global scale, to examine the
global nature of climate change and its impact (Paw U, 2000).

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Remote Sensing of the Environment and Vegetation
Remote sensing detects and measures the characteristics of a target without being in physical touch
with it. Information about the object is derived through electromagnetic energy. Aircraft and
satellites are the main platforms for remote-sensing observations. Aerial photographs are the
original form of remote sensing and remain the most widely used method. Infrared thermometry
provides a way to determine the surface temperatures of plants and animals. Precise handheld
infrared thermometers are commercially available to provide these measurements. The technology
allows the measurement of the surface temperature with a resolution of a few square centimeters.
The development and deployment of earth satellites in the 1970s brought a revolution in remote
sensing. Remote sensing now provides a sequence of reliable and irreplaceable information for
agriculture planning and management (Maracchi, Pérarnaud, and Kleschenko, 2000).
Weather and Climate Information for Agriculture
The agriculture industry is the most sensitive to variability in weather and climate. Throughout the
world, efforts have been made to provide agriculture with a specifically focused weather service.
Most countries of the world have developed programs to provide agroclimatological services.
Unfortunately, in many countries there is a lack of coordination and cooperation to link agencies
representing agriculture and meteorology in their efforts to advise farmers of weather- related risk
management. This lack of cooperation has adversely affected improvements and further
development in agro-advisory services. Furthermore, due to a lack of financial support, the
network of meteorological stations does not adequately cover various agroclimatological zones to
meet potential needs. Conflicts within and between countries often halt the collection and
exchange of weather data. This has a detrimental impact on projects in which analysis of weather
and climate data is attempted.
Crop-Related Climate Data Archives
Early studies dealing with relationships between yields and climate were accomplished using
limited climatic data and primitive computational procedures. The advent of the computer era saw

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the development of new methods for storing historical data. Computer programs are now available
that can electronically archive huge amounts of climatic data. These archives have further
enhanced the evaluations of weather and climate risk for agriculture. The World Meteorological
Organization (WMO) supports the sharing of computerized climate data in all countries of
theworld (Decker, 1994).
Climate Change and Impact
Over the past 100 years, human activities have significantly altered the earth’s atmosphere.
Increases in the concentrations of greenhouse gases have led to warming of the earth’s surface. An
accumulating body of evidence suggested that by the last decade of the twentieth century global
warming had already made significant negative impacts in a large number of regions. The menace
of global climate change became a central issue of investigation in the 1990s and beyond. The
investigations considered the effects of global warming on individual plants, plant stands, and
entire vegetation units from regional to global scales (Overdieck, 1997). The investigations were
not confined only to plants; the impact on hydro-resources, livestock, insect pests, and diseases
has also been investigated.
Soil Temperature
Soil temperature is an important environmental factor in plant growth and distribution. In
comparison to air temperature, the amplitude of variation in soil surface temperature is much more
pronounced because of the varying characteristics and composition of soil.
Factors Affecting Soil Temperature:
 Aspect and slope: These factors are of great importance in determining soil temperature
outside the tropics. In the Northern Hemisphere, a south-facing slope is always warmer than a
north-facing slope or a level plain. The reverse is the case in the Southern Hemisphere. The
difference in soil surface temperature exceeds the difference in air temperature.

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 Tillage: By loosening topsoil and creating mulch, tillage reduces the heat flow between the
surface and subsoil. Because a mulched surface has a greater exposed area and the capillary
connection with moist layers below is broken, cultivated soil has greater temperature amplitude
than uncultivated soil. At noon, the air temperature 2.5 cm above the soil surface can be 5 to
10 C higher in cultivated soil as compared to uncultivated soil.
 Soil texture: Because of lower heat capacity, sandy soils warm up and cool down more rapidly
than clay soils; hence, they are at a higher temperature during the day and a lower temperature
at night.
 Organic matter: Organic matter reduces the heat capacity and thermal conductivity of soil,
increases its water-holding capacity, and has a dark color which increases its solar radiation
absorptivity. In humid climates, because of a large water content, peat and marsh are much
cooler than mineral soils in spring and warmer in winter. However, when organic soils are dry,
they become warmer than mineral soils in summer and cooler in winter.
Impact of Soil Temperature and Plant Growth
 Soil temperatures influence the germination of seeds, the functional activity of the root system,
the incidence of plant diseases, and the rate of plant growth.
 After germination, soil temperature is important for the vegetative growth of crops.
 For each species, a favorable soil temperature is needed for ion and water uptake.
 The daytime soil temperature is more important than the nighttime temperature, because it is
necessary to maintain a favorable internal crop water status to match the high evaporation rate.
 Soil temperature correlated positively with root yield and negatively with sugar content.
 Optimal soil temperature for growth of wheat plant roots during the vegetative stage is below
20°C and is lower than that for the shoots.
 Temperatures higher than 35°C have been shown to reduce terminal root growth and accelerate
its senescence.
 Root growth may cease altogether if soil temperatures drop below 2°C.
 High (40 c+) or low (3 C-) affects the photosynthesis process negatively.

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Cardinal Temperature
Three temperatures of vital plant activity have been recognized, which are often termed cardinal
points. The cardinal points can be measured only approximately because their position is related
to external conditions, the duration of exposure, the age of the plant, and its previous treatment.
1. A minimum temperature below which no growth occurs: For typical cool-season crops, it
ranges between 0 and 5 C, and for hot-season crops between 15 and 18 C.
2. An optimum temperature at which maximum plant growth occurs: For cool-season crops,
it ranges between 25 and 31 C, and for hot-season crops between 31 and 37 C.
3. A maximum temperature above which the plant growth stops: For cool-season crops, it
ranges between 31 and 37 C, and for hot-season crops between 44 and 50 C.
Plant injury due to Sudden Temperature Change
Plant injury due to sudden temperature change can occur in the following way-
1. Injury due to imbalance of leaf temperature and air temperature
2. High temperature injury
3. Low temperature injury

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1. Injury due to imbalance of leaf temperature and air temperature:
Under normal conditions, leaf temperature remains around the ambient temperature but differs
under certain situations. At a temperature of about 33 C, there is a tendency for equality between
air and leaf temperature. Below this temperature, leaves tend to be warmer than the air and vice
versa. Where the temperature exceeds 33 C, leaves appear to suffer from water stress.
 Leaves exposed to sun: Thick leaves that are not transpiring actively in still air are several
degrees warmer than the air. Under intense radiation and high humidity, some leaves may
be at a temperature 15 C higher than the air. Likewise, under very hot and low humidity
conditions, leaf temperature can be as much as 10 C higher than the air. Where plants do
not suffer for want of moisture, the difference between leaf and air temperature is very
small.
 Leaves under shade: Leaves shaded from direct sunlight are usually somewhat warmer
than the surrounding air.
 Leaves exposed to a clear night: At night when the sky is clear, leaf temperature is usually
lower than the air temperature. During a cold and clear night, a leaf may be around 2 C
cooler than the surrounding air.
 Leaves exposed to a cloudy night: With cloud cover, the difference in air and leaf
temperature is small. In certain cases the leaf temperature may be slightly higher than air
temperature.
2. High Temperature Injury:
 High temperature results in the desiccation of the plant and disturbs the balance between
photosynthesis and respiration.
 At temperatures higher than the optimum cardinal, the physiological activity declines as a
consequence of inactivation of enzymes and other proteins.
 Leaf functions are disturbed at about 42 C, and lethal effects on active shoot tissues
generally occur in the range of 50 to 60 C.

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 High temperature affects the grain size, weight and germination as well for the wheat and
rice.
 Serious damage to fruit and vegetable crops resulting from excessively high temperature
has also been recorded.
 The higher the temperature, the greater is the rate of respiration, which results in the rapid
exhaustion of food reserves of seeds.
 Temperatures on the sunny side of the bark on stems during hot afternoon and late night
undergo great fluctuations. The injury inflicted because of this short period fluctuation in
temperature is known as sun scald.
 Stem girdle is another injury associated with high temperature. Exceptionally high
temperature at the soil surface and the adjoining laminar sublayer of the air frequently
scorches the short stems. The scorching of the stem is known as stem girdle.
3. Low Temperature Injury:
 Suffocation: Small plants may suffer from deficient oxygen when covered with densely
packed snow. When suffocated, certain toxic substances accumulate in contact with roots
and crowns and tend to inhibit the diffusion of carbon dioxide.
 Physiological Drought and Desiccation: Spring drought sometimes occurs in coniferous
trees in cool temperate climates. This results from excessive transpiration and a time lag in
absorption of moisture from the soil, caused by a warm period when the soil is still frozen.
The result is an internal moisture deficit sufficient to cause death of the twigs. The
decreased water absorption by plants at low temperatures is the combined effect of the
decreased permeability of the root membrane and increased viscosity of water. This results
in increased resistance to water movement across the living cells of the roots.
 Heaving: Injury to a plant is caused by the soil layer lifting upward from the normal
position and causing the root to stretch or break at a time when the plant is growing.
Sometimes the roots are pushed completely above the soil surface. After thawing, it is

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difficult for the roots to become firmly established, and the plants may die because of this
mechanical damage and desiccation.
 Chilling: In temperate climates, two types of injuries occur because of low temperature.
These are delayed growth and sterility. For example, rice yield decreases due to insufficient
grain maturation caused by low temperatures during the ripening period. When flowering
is delayed by low temperatures at a certain stage before heading, insufficient time is
available to the grains to ripen fully before frost occurs in autumn.
 Freezing Injury: Plant parts or an entire plant may be killed or damaged beyond repair as
a result of actual freezing of tissues. Freezing damage is caused by the formation of ice
crystals, first in the intercellular spaces and then within the cells. Ice within the cells causes
more injury by mechanical damage disrupting the structure of the protoplasm and plasma
membrane. Freezing of water in intercellular spaces results in withdrawal of water from
the cell sap, and increasing dehydration causes the cell to die.
Effective Use of Rainfall
Effective Precipitation (EP) is the amount of precipitation that is actually added and stored in the
soil. During drier periods less than 5 mm of daily rainfall would not be considered effective, as
this amount of precipitation would likely evaporate from the surface before soaking into the
ground. Effective precipitation enters the soil and becomes available to the plant.
If the precipitation is 25-30 mm, there would be 50% usage in agriculture. The percentage will rise
with the frequency of precipitation.
Components of Effective Rainfall: According to FAO,
1. Rainfall & irrigation
2. Surface Run-off
3. Rooting Depth
4. Deep Percolation Losses
5. Evapotranspiration

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Measurement of Effective Rainfall:
There have been several models and methods of measuring effective model. One of them is
narrated below.
Patwardhan and Nieber (1987) proposed a soil-water balance model based on the equation of
conservation of water in the soil profile. The water balance of the entire soil profile is considered
in terms of individual processes:
P + I – R – RN = ET + D + ∆S
Where P is rainfall, I is irrigation, R is runoff, RN is rainfall interception, ET is evapotranspiration,
D is deep drainage, and ∆S is the change in water content in the soil profile. All the measurements
are in mm of water.
Effective rainfall is defined in the model as being that portion of the rainfall that infiltrates into the
soil and does not contribute to deep percolation. This is expressed as:
EP = (P – RN – R)
Where EP is the effective rainfall. The time scale on which the effective rainfall can be defined
can be as small as one day; however, there is no upper limit.
Other Methods:
 Dastane (1974) recommended two methods for estimation of effective rainfall. In the first
method, a percentage of rainfall varying from 50 to 80 percent was assumed to be effective. In
the second method, rainfall less than 6.25 mm or in excess of 75 mm on any day, or a rainfall
in excess of 125 mm in 10 days, is considered to be ineffective.
 The U.S. Department of Agriculture (USDA) Soil Conservation Service (SCS) method
estimates the effective rainfall by the evaporation/precipitation ratio method (FAO, 1977).
Tables are given in which relationships are shown between average monthly effective rainfalls
and mean monthly rainfall for different values of average monthly crop evapotranspiration
values. For use in irrigation, a net depth of irrigation water that can be stored effectively in the

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root zone is assumed to be 75 mm. Correction factors are given for different depths that can be
stored.
 Ashok Raj (1979) proposed a method for forecasting rainfall characteristics, such as the onset
of an effective monsoon, based on the following criteria:
a. The first day’s rain in the seven-day spell, signifying the onset of an effective monsoon,
should not be less than e mm, where e is the average daily evaporation.
b. The total rain during the seven-day spell should not be less than 5e + 10 mm.
c. At least four of these seven days should have rainfall, with not less than 2.5 mm of rain
on each day.
 Stern and Coe (1982) used a general definition for the start of rains with these criteria:
a. The event making the start of the season was not considered until after a stated date D.
b. An event E then indicates a potential start date, defined as the first occurrence of at least
x mm rainfall totalled over t consecutive days.
c. The potential start could be a false start if an event F occurs afterward, where F was
defined as a dry spell of n or more days in the next m days.
For determining the start of rains at Kano, Nigeria, D was taken as May 1, x as 20 mm in two
consecutive days, and F as a ten-day spell in the next 30 days. By using frequency distribution,
they determined the potential start and false starts at different probability levels.
Evaporation and Potential Evapotranspiration
Potential evapotranspiration or PE is a measure of the ability of the atmosphere to remove water
from the surface through the processes of evaporation and transpiration assuming no control on
water supply. Actual evapotranspiration or AE is the quantity of water that is actually removed
from a surface due to the processes of evaporation and transpiration.
Scientists consider these two types of evapotranspiration for the practical purpose of water
resource management. Around the world humans are involved in the production of a variety of
plant crops. Many of these crops grow in environments that are naturally short of water. As a result,
irrigation is used to supplement the crop's water needs. Managers of these crops can determine

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how much supplemental water is needed to achieve maximum productivity by estimating potential
and actual evapotranspiration. Estimates of these values are then used in the following equation:
Crop water need = potential evapotranspiration - actual evapotranspiration
Over a land surface covered with vegetation, evaporation involves the following processes:
1. Movement of water within the soil toward the soil surface or toward the active root system of
the plants;
2. Movement of water into the roots and then throughout the plant tissues to leaf surfaces;
3. Change of water into vapor at the soil surface or at the stomata of plants;
4. Change of rain water or snow from the outer surface of plants into vapor; and
5. The physical removal of water vapor from the boundary layer.
Penman-Monteith estimates and Penman estimates are two methods of measuring them. Penman-
Monteith method is as below-
Here,
Rn is net radiation at crop surface (MJ m–2/day).
Rs is shortwave radiation (MJ m–2/day).
G is soil heat flux (MJ m–2/day).
T is average daily temperature (°C).
U is wind speed at 2 m above ground surface (m·s–1).
ea is saturation vapor pressure at air temperature (kPa).
ed is actual air vapor pressure (kPa).
∆ is slope of saturation vapor pressure/temperature curve (kPa/°C).
γ is psychrometric constant (kPa/°C).

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Water Use and Loss in Irrigation
 Most surface-irrigated areas are supplied with water from a canal system.
 In general, supply rules are rigid, and often the time interval between successive deliveries is
too long. Irrigators tend to compensate for this by applying all the water they are entitled to
use. This leads to substantial water wastage through evaporation and percolation.
 Excessive applications also result in reduced crop growth, leaching of plant nutrients, and
waterlogging.
 According to an estimate (FAO, 1994), on average, only 45 percent of the water is used by the
crop, with an estimated 15 percent lost in the water conveyance system, 15 percent in field
channels, and 25 percent in inefficient field applications.
Drought and Its Classification
In general, a drought is when a shortfall in precipitation creates a shortage of water, whether it is
for crops, utilities, municipal water supply, recreation, wildlife, or other purposes. According to a
WMO definition (Bogardi et al., 1994), “drought is a sustained, extended deficiency in
precipitation.” Operational definitions of drought vary from place to place and are crucial to
identify the beginning and intensity of drought.

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There are three main types of drought: meteorological, agricultural, and hydrological (National
Drought Mitigation Center, 1996c).
1. Meteorological drought is an expression of rainfall departure from normal over some
period of time. Meteorological drought definitions are usually region specific and are based
on a thorough understanding of the climatology of the region.
2. Agricultural drought occurs when there is not enough soil moisture to meet the needs of
crops at a particular time.
3. Hydrological drought refers to deficiencies in surface and subsurface water supplies. It
is measured as stream flow and as lake, reservoir, and groundwater levels.
Drought Assessment Methods
There are 4 methods of drought analysis-
1. Rainfall analysis
2. Remote Sensing
3. Simulation models
4. More than one simulation
Rainfall analysis
Drought is a consequence of rainfall deficiency in relation to potential water loss through
evaporation. Analysis of rainfall is therefore the primary basis of identification of drought.
However, a number of pitfalls have to be kept in mind while depending on rainfall data for
assessing drought.
Rainfall measurements are at points that are often widely separated. Maps of rainfall deficiency or
surplus drawn on the basis of point measurements are frequently far from the reality of the
conditions some distance from these points. Rainfall occurring at one time of the year can be
carried over under fallow to be used at other times of the year, making average monthly rainfall
values irrelevant. Results from various studies suggest that ranking the year according to rainfall
may be quite different to ranking the year from simulated pasture growth. Failure of rain at the
optimum time may downgrade the otherwise average rainfall conditions in terms of production

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potential. Average rainfall conditions mask the influence of rainfall intensity and rainy-spell
duration on the actual performance of crops and pastures.
An examination of temporal rainfall records in Australia at some locations has shown a tendency
toward higher rainfall in the second half of this century. If this observation turns out to be true,
then the emerging pattern is likely to be strengthened further under the global warming scenario
and will have a significant impact on the identification and temporal comparisons of droughts on
the basis of severity and impacts. By the present definition, there may not be any drought
exceptional circumstances event in the near future to be compared with those that occurred in first
half of the twentieth century.
Simulation Models
Simulation models hold great promise in objective identification of drought and drought
exceptional circumstances because they hold the potential to integrate the climate and farming
dimensions of production sys tems. At the same time, simulation models are not capable now, nor
will they be in the near future, of replacing other measures of drought identification.
Any minor wrong information about plant characteristics or soil parameters included in running
the simulation can greatly influence the output of the model. Efforts to overcome this shortcoming
need to be balanced against the expected gains over the simpler models.
The majority of the models can easily identify a major drought event, but they differ considerably
in highlighting marginal events. Some models have a tendency to amplify minor events, while at
other times major events are presented in a suppressed form. The differing results can create a
confusing situation. Modeling living systems is very complex. Models available at present are
capable of giving outputs only approximating reality.
Remote Sensing
Satellite-derived images are useful in broad-scale assessment of greenness of ground cover,
especially the vegetation response to a rainfall event. Another major value of remote sensing

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information is for spatial and temporal validation of the simulation models. However, remote
sensing has inherent limitations in providing a total solution to drought monitoring.
Images from satellites give poor information on biomass, and tree cover confounds the signals.
Interpretations of the images do not consider the effects of vegetation structure and cover.
Remotely sensed data products currently available contain a lot of noise from the instruments
onboard and the atmosphere. This noise is of sufficient magnitude to disqualify remotely sensed
products for use in drought analysis, and if used unhindered, the state-of-the-art products may not
stand up to the test of law courts.
Data availability from remote sensing satellites is not guaranteed because the majority of the
countries in the world purchase data from foreign sources. Furthermore, a failure of systems
onboard a satellite at a critical time during the drought season may render the previous satellite
information completely useless. The remotely sensed data are currently available for less than two
decades. This is too short a period to identify an exceptional circumstance event on a temporal
scale. No future projection of the intensity and magnitude of the event is possible through remote
sensing measurements. These limitations of remotely sensed information suggest that it cannot be
used exclusively in defining a drought or drought exceptional circumstances. It is a supplement to
other measures of the event.
More than One Model
This leads to the conclusion that a combination of methods—rainfall analysis, crop and pasture
simulation, and monitoring the health of vegetation through remote sensing—supported with field
surveys is the most realistic approach to assess the extent and intensity of drought.
SPI and SPEI
SPI
The Standardized Precipitation Index (SPI) is based on the fact that a deficit of precipitation has
different impacts on the groundwater, reservoir storage, soil moisture, snowpack, and stream flow
(McKee, Doesken, and Kleist, 1993). The SPI quantifies the precipitation deficit for multiple time

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scales (3, 6, 12, 24, and 48 months). These time scales reflect the impact of drought on the
availability of the different water resources. Soil moisture conditions respond to precipitation
anomalies on a relatively short scale, while groundwater, stream flow, and reservoir storage reflect
the longerterm precipitation anomalies. SPI is calculated by taking the difference of the
precipitation from the mean for a particular time scale and then dividing by the standard deviation.
Because precipitation is not normally distributed for time scales shorter than 12 months, an
adjustment is made which allows the SPI to become normally distributed. Thus, the mean SPI for
a time scale and location are zeros and the standard deviation is one. This is an advantage, because
the SPI is normalized so that wetter and drier climates can be represented in the same way.
SPEI
The Standardized Precipitation Evapotranspiration Index (SPEI) is an extension of the widely used
Standardized Precipitation Index (SPI). The SPEI is designed to take into account both
precipitation and potential evapotranspiration (PET) in determining drought. Thus, unlike the SPI,
the SPEI captures the main impact of increased temperatures on water demand. Like the SPI, the
SPEI can be calculated on a range of timescales from 1-48 months. At longer timescales (>~18
months).
It can be used for determining the onset, duration and magnitude of drought conditions with respect
to normal conditions in a variety of natural and managed systems such as crops, ecosystems, rivers,
water resources, etc.

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Remote Sensing Application in Agriculture
1. Crop production forecasting: Remote sensing is used to forecast the expected crop production
and yield over a given area and determine how much of the crop will be harvested under specific
conditions. Researchers can be able to predict the quantity of crop that will be produced in a given
farmland over a given period of time.
2. Assessment of crop damage and crop progress: In the event of crop damage or crop progress,
remote sensing technology can be used to penetrate the farmland and determine exactly how much
of a given crop has been damaged and the progress of the remaining crop in the farm.
3. Horticulture, Cropping Systems Analysis: Remote sensing technology has also been
instrumental in the analysis of various crop planting systems. This technology has mainly been in
use in the horticulture industry where flower growth patterns can be analyzed and a prediction
made out of the analysis.
4. Crop Identification: Remote sensing has also played an important role in crop identification
especially in cases where the crop under observation is mysterious or shows some mysterious
characteristics. The data from the crop is collected and taken to the labs where various aspects of
the crop including the crop culture are studied.
5. Crop acreage estimation: Remote sensing has also played a very important role in the
estimation of the farmland on which a crop has been planted. This is usually a cumbersome
procedure if it is carried out manually because of the vast sizes of the lands being estimated.
6. Crop condition assessment and stress detection: Remote sensing technology plays an important
role in the assessment of the health condition of each crop and the extent to which the crop has
withstood stress. This data is then used to determine the quality of the crop.
7. Identification of planting and harvesting dates: Because of the predictive nature of the remote
sensing technology, farmers can now use remote sensing to observe a variety of factors including
the weather patterns and the soil types to predict the planting and harvesting seasons of each crop.

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8. Crop yield modelling and estimation: Remote sensing also allows farmers and experts to
predict the expected crop yield from a given farmland by estimating the quality of the crop and the
extent of the farmland. This is then used to determine the overall expected yield of the crop.
9. Identification of pests and disease infestation: Remote sensing technology also plays a
significant role in the identification of pests in farmland and gives data on the right pests control
mechanism to be used to get rid of the pests and diseases on the farm.
10. Soil moisture estimation: Soil moisture can be difficult to measure without the help of remote
sensing technology. Remote sensing gives the soil moisture data and helps in determining the
quantity of moisture in the soil and hence the type of crop that can be grown in the soil.
11. Irrigation monitoring and management: Remote sensing gives information on the moisture
quantity of soils. This information is used to determine whether a particular soil is moisture
deficient or not and helps in planning the irrigation needs of the soil.
12. Soil mapping: Soil mapping is one of the most common yet most important uses of remote
sensing. Through soil mapping, farmers are able to tell what soils are ideal for which crops and
what soil require irrigation and which ones do not. This information helps in precision agriculture.
13. Monitoring of droughts: Remote sensing technology is used to monitor the weather patterns
including the drought patterns over a given area. The information can be used to predict the rainfall
patterns of an area and also tell the time difference between the current rainfall and the next rainfall
which helps to keep track of the drought.
14. Land cover and land degradation mapping: Remote sensing has been used by experts to map
out the land cover of a given area. Experts can now tell what areas of the land have been degraded
and which areas are still intact. This also helps them in implementing measures to curb land
degradation.
15. Identification of problematic soils: Remote sensing has also played a very important role in
the identification of problematic soils that have a problem in sustaining optimum crop yield
throughout a planting season.

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16. Crop nutrient deficiency detection: Remote sensing technology has also helped farmers and
other agricultural experts to determine the extent of crop nutrients deficiency and come up with
remedies that would increase the nutrients level in crops hence increasing the overall crop yield.
17. Reflectance modeling: Remote sensing technology is just about the only technology that can
provide data on crop reflectance. Crop reflectance will depend on the amount of moisture in the
soil and the nutrients in the crop which may also have a significant impact on the overall crop
yield.
18. Determination of water content of field crops: Apart from determining the soil moisture
content, remote sensing also plays an important role in the estimation of the water content in the
field crops.
19. Crop yield forecasting: Remote sensing technology can give accurate estimates of the
expected crop yield in a planting season using various crop information such as the crop quality,
the moisture level in the soil and in the crop and the crop cover of the land. When all of this data
is combined it gives almost accurate estimates of the crop yield.
20. Flood mapping and monitoring: Using remote sensing technology, farmers and agricultural
experts can be able to map out the areas that are likely to be hit by floods and the areas that lack
proper drainage. This data can then be used to avert any flood disaster in future.
21. Collection of past and current weather data: Remote sensing technology is ideal for collection
and storing of past and current weather data which can be used for future decision making and
prediction.
22. Crop intensification: Remote sensing can be used for crop intensification that includes
collection of important crop data such as the cropping pattern, crop rotation needs and crop
diversity over a given soil.
23. Water resources mapping: Remote sensing is instrumental in the mapping of water resources
that can be used for agriculture over a given farmland. Through remote sensing, farmers can tell
what water resources are available for use over a given land and whether the resources are
adequate.

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24. Precision farming: Remote sensing has played a very vital role in precision agriculture.
Precision agriculture has resulted in the cultivation of healthy crops that guarantees farmers
optimum harvests over a given period of time.
25. Climate change monitoring: Remote sensing technology is important in monitoring of climate
change and keeping track of the climatic conditions which play an important role in the
determination of what crops can be grown where.
26. Compliance monitoring: For the agricultural experts and other farmers, remote sensing is
important in keeping track of the farming practices by all farmers and ensuring compliance by all
farmers. This helps in ensuring that all farmers follow the correct procedures when planting and
when harvesting crops.
27. Soil management practices: Remote sensing technology is important in the determination of
soil management practices based on the data collected from the farms.
28. Air moisture estimation: Remote sensing technology is used in the estimation of air moisture
which determines the humidity of the area. The level of humidity determines the type of crops to
be grown within the area.
29. Crop health analysis: Remote sensing technology plays an important role in the analysis of
crop health which determines the overall crop yield.
30. Land mapping: Remote sensing helps in mapping land for use for various purposes such as
crop growing and landscaping. The mapping technology used helps in precision agriculture where
specific land soils are used for specific purposes.
GIS Application in Agriculture
 Crop mapping yield estimation
 Crop assessment and Crop health
 Irrigated landscape mapping
 Application development for GIS agriculture
 Soil and irrigation amendment analysis
 Suitability assessment studies

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 Erosion identification and remediation
 Agricultural mapping for detailed vegetation cover and monitoring
 Change detection studies and developing crop models
 Damage and land degradation assessment studies
 Elevation models for efficient drainage
Models
A model is a schematic representation of our conception of a system. A model brings into mind
the functional form of a real object, such as children’s toys, a tailor’s dummy, and mock-ups of
buildings and structures to be later constructed in the real forms. Models also construct objects or
situations not yet in existence in real form. A model can also be referred to as a representation of
a relationship under consideration and may be defined as an act of mimicry. Models can be broadly
divided into statistical models and dynamic simulation models.
Statistical Models
Statistical models are those that do not require detailed information about the plant involved but
rely mainly on statistical techniques, such as correlation or regression, relating to the appropriate
plant and environmental variables (Norman, 1979). Most statistical models are crop-yield weather
models, which are applied to estimate yield over large areas with variable success. The regression
coefficients themselves are not necessarily related to the important processes and therefore are
highly variable with crop type, region, etc. Many studies are required to produce the regression
equations necessary for the widespread application of this kind of model. A great advantage of
these simple crop-weather models is that they use readily available weather data. Although results
are not very accurate, the statistical model is able to recognize the years that bumper crops and
crop failures can be expected, several weeks prior to harvest. Regression models are attractive
because of their simple and straightforward relationship between yield and one or more
environmental factors, but these are not accurate enough to be used for other areas and other crops.
Despite this limitation, they are used extensively for the prediction of yield of a single crop over a

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large region, with a variety of soils, agronomic practices, and insect-disease problems. A
combination of such factors is still beyond the dynamic simulation models. It is a technique well
worth retaining in the arsenal of tools available to the agricultural climatologist (Whisler et al.,
1986).
Dynamic Simulation Models
A dynamic model is the one whose output varies with time and in which processes are
characterized. To characterize processes, the state variables must be known. State variables are
those necessary to define the state of the system at a point in time. Dynamic simulation crop models
predict changes in crop status with time as a function of biogenetic parameters (Hume and
Callander, 1990). Simulation means that the model acts like a real crop, gradually germinating and
growing leaves, stems, and roots during the season. In other words, simulation is the process of
using a model dynamically by following a system over a time period. Dynamic models can be
classified as preliminary models, comprehensive models, and summary models (Penning de Vries
et al., 1989). Preliminary models have structure and data that reflect current scientific knowledge.
These are simple because insight is at the exploratory level. A comprehensive model is a model of
a system in which essential elements are thoroughly understood and much of this knowledge is
incorporated. Summary models are abstracts of comprehensive models and are found at production
levels. Comprehensive dynamic models predict yield much closer to reality than do the regression
models. However, the more accurate the dynamic model is, the more information is required for
initialization and about driving variables. In many cases these may not be available, hence the
regression models may still be our best option. Developing a comprehensive, dynamic crop
simulation model requires a multidisciplinary team. Plant physiologists, agronomists, and soil
scientists are needed to help define both the overall framework of the problem and the specificities
of the environment and plant growth relationship. Entomologists and plant pathologists are
required to define the insect and pathogen subsystems that are important parts in the crop
ecosystems. An agrometeorologist selects and contributes data about weather and microclimate
fluxes in and around the plant canopies. A computer programmer selects the computer language

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and develops the overall framework of the model (Ritche et al., 1986). After designing the first
version of the model and analyzing the results of its output, faults are invariably found, which
require changes in the structure of the model. These changes require additional study and
verification, and the loop continues. Furthermore, in the process of development, the initial
representation of the modeling process is improved upon and the range of experimental data used
is widened. In the final verification process, it is important to consider an independent data set that
was not used in the development of the model (Guardrian, 1977).
Decision Support Systems (DSS)
Decision support systems (DSS) are integrated software packages comprising tools for processing
both numerical and qualitative information. A DSS points the way for better decision making in
the cropping and pastoral industries. It offers the ability to deliver the best information available,
quickly, reliably, and efficiently.
The choices of planting time, varietal selection, grazing strategies, and fertilizer, irrigation, and
spray applications are complex decisions to be made at the farm level. These are important and
decisive because they cannot be postponed, are irreversible, represent a substantial allocation of
resources, and have a wide range of outcomes, with consequences that impact the farm business
for years to come. They are also hard decisions because they are characterized by uncertainty,
mainly due to the highly variable climate. They are complex both in terms of the number of
interacting factors and the trade-offs between risk and reward. A successful decision support
system focuses on such decisions. A key element in the success of a DSS is the development of
trust in its reliability and the willingness and ability of the targeted users to utilize the system.
Components of DSS:
DSS components may be classified as:
1. Inputs: Factors, numbers, and characteristics to analyze
2. User knowledge and expertise: Inputs requiring manual analysis by the user
3. Outputs: Transformed data from which DSS "decisions" are generated

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4. Decisions: Results generated by the DSS based on user criteria
Examples of DSS:
Australian RAINMAN is a computer package that helps examine historical records of rainfall
and temperature, analyzes monthly and daily rainfall records, and forecasts seasonal
rainfall based on SOI (Southern Oscillation Index) and Indian Ocean sea-surface
temperature.
TACT calculates probability distributions of wheat yields and gross margins at a given location.
Using predominantly empirical relationships, the package predicts wheat performance on
a daily time step. Predictions of the timing of major phenological events are also available.
PYCAL (Potential Yield Calculator) is a computer program to monitor current seasonal rainfall
against the historic record and to estimate stored soil water and potential yield for a range
of cereal, pulse, and oilseed crops.
SOWHAT is a decision support tool for wheat farmers in areas of Mediterranean climate. It builds
on information from the years with a high probability of above-average wheat yields and
those with a low probability of good yields. Subsequently, it uses this information to
develop a sowing strategy. SOWHAT enables farmers to use their own farm records to
develop their strategies for maximizing farm wheat yields.
Whopper Cropper is designed to apply cropping systems modeling and seasonal climate
forecasting to crop management. It meets the demand of extension professionals for access
to the cropping systems modeling capability of APSIM (Agricultural Production Systems
SIMulator). It provides information on the impact of climate risk on crop yields for crop
management alternatives beyond the experience of individual farmers. Whopper Cropper’s
graphical user interface is designed to enable farmers to explore management strategies at
the beginning of each cropping season.
GrassGro predicts pasture growth and production from a mob of sheep or cattle grazing a paddock
or group of paddocks in any enterprise in a Mediterranean climate. Applications of
GrassGro in use are to (1) compare the current season’s pasture production with the same

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seasonal periods in the past, (2) explore the likely effects of different plant characteristics
on the productivity of grazing animals, (3) compare stocking rates, (4) estimate gross
margins from an enterprise, and (5) use as a strategic planning tool for the management of
breeding stock and supplementary feed needs.
Aussie Grassland or Australian Grassland and Rangeland Assessment by Spatial Simulation
(Aussie GRASS) is a spatial modeling framework for assessing the condition of Australia’s
grazing lands. Aussie GRASS gives information on pasture growth that allows estimates
of long-term safe stocking rates.
Sustainable Production
Temperature and the quantity, variability, and seasonal distribution of rainfall will determine the
type of crops and livestock enterprises suited to a given location. These parameters, combined with
soil type and landform, also determine what levels of production (e.g., stocking rate or cropping
area) are appropriate to avoid the threat of degrading the natural resource base on which the
enterprise depends. In particular, these climate characteristics will determine the
 enterprise orientation (e.g., mainly cropping, integrated crop-livestock, or mainly livestock);
 ability to diversify into other enterprises (influenced by suitable plant cultivars and livestock
breeds);
 season of cropping (summer, summer and winter, winter), which is influenced by rainfall
distribution and the capacity of the soil to store water;
 degree of flexibility in choosing rotations and enterprises (Tow and Schultz, 1991).

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Climatic patterns and sequence of crop rotations.
Developing Resilience
Resilience refers to the ability a farming system has in withstanding unexpected and sometimes
severe disturbances in the form of climatic extremes (e.g., prolonged drought), pests and diseases,
changes in markets, and input costs. The management team determines this “ability” and the plans
and strategies they have in place to reduce their exposure to these disturbances and, if need be, to
“bounce back.”
The resilience of different agricultural systems will depend on the intensity of production. For
example, grazing systems that rely on high stocking rates are more vulnerable in dry seasons. The
resilience of agricultural systems can be improved by the following approaches:
 Diversify crop and livestock systems. For example, diversification of crops and planting times
reduce the impact of a poor season, especially for areas such as the northern wheat belt of
eastern Australia (Ridge and Wylie, 1996a).
 Grow productive, deep-rooted perennial pasture species that can respond to and make efficient
use of rainfall throughout the year. This includes maintaining native perennial pasture species,
such as Danthonia (wallaby grass), which have grazing value and a tolerance of dry weather.

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 Match livestock demand and pasture supply closely to reduce the prospect of feed deficits.
Aligning peak animal demand (i.e., late pregnancy and lactation) with peak pasture supply will
maintain pasture quality while reducing the need for supplementary feeding.
 Conserve and store fodder to overcome periods of feed deficiency. Fodder reserves should be
increased as the stocking rate on a property increases; this will reduce the exposure to price
changes for supplementary feeding in dry times.
 Use flexible rotational grazing rather than set stocking to make it easier to ration the feed
supply and assess the amount of standing feed reserves available in dry times.
 Use different crop types and varieties and spread planting over a number of weeks to reduce
the exposure of crops to weather damage at critical stages such as flowering and harvest time
(Ridge and Wylie, 1996b).
 Use minimum- or zero-tillage systems that make efficient use of rainfall and that can outyield
conventionally sown crops in dry years. Minimum- tillage cropping systems also provide
greater flexibility in the timing of sowing operations.
 Use fallows to reduce a crop’s reliance on growing-season rainfall.
 Provide shelter and windbreaks for livestock to reduce feed demand, improve animal
production, and minimize livestock losses.
 Correct nutrient deficiencies and implement an integrated pest management program to
improve the vigor of crops and pastures so they can better cope with climate variability.
 Use irrigation, where the opportunity exists, to overcome water deficits at critical growth stages
of crops and pastures.
 Use netting to protect horticultural crops from hail damage.
 Carry out farm operations in a timely manner.
 Store or carry over grain or other products from productive years when prices are low to either
use or sell at a later time.
 Reduce fuel loads and put in firebreaks before the bushfire season.

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 Broaden the income base through off-farm investments and manage price risk by using forward
contracts, futures, and hedging in response to commodity market fluctuations or seasonal
forecasts.
Managing the Extreme
The experience of the extreme effects of climate, droughts, and floods generally provide the
catalyst for change in management practices. However, many farmers tend to downplay the
likelihood of these extreme events when not operating in them (Nicholls, 2000). This is made
evident in the following quote: “We farmers should be planning for drought every day. What
causes change for us is mostly drought. When we aren’t in a drought we don’t think about it” (Tim
Wright, grazier, Uralla, NSW, personal communication).
The harsh experience of drought and floods shows that it is essential to have a strategy in place.
These strategies should be based on local experience, an understanding of the local climate record,
and the frequency of these events. Once developed, the strategies can be further guided and adapted
according to seasonal forecasts and by calculating rainfall deciles to assess how dry or wet a month
is compared to local historical rainfall figures. Deciles are calculated by ranking the rainfall record
from lowest to highest recordings into 10 percent bands. Probability charts using rainfall deciles
can be used to determine the probability of a certain amount of rainfall for making tactical
decisions.
Droughts
Droughts are frequent but irregular events. Farmers and graziers generally refer to drought when
the available rainfall over a period of time is not enough to give adequate plant growth and there
is a major loss of agricultural production. Within some agricultural industries there can be
differences of emphasis; references to a “feed” drought, “protein” drought, and “water” drought
are common in the livestock sector.

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During a drought, farm managers face a multitude of issues. By developing a personal plan, based
on an assessment of resources and climatic risks, farm managers will be in a better position to
manage a property through drought. A drought plan has four major components:
1. Identification of the risks to enterprises.
This requires an estimate of the critical time(s) for rainfall and the absolute minimum needed to
operate. This will depend on the enterprises. For example, breeding programs are at greater risk
than stock trading.
2. Analysis of the local climate to find the chances of the risk occurring.
This analysis is used to answer the following questions:
How often has the essential rain failed to come?
How long do low rainfall periods last on average?
Are they more likely at one time of the year?
What seasonal forecasting tools can be used?
3. Identification of factors to monitor.
As well as measuring rainfall directly, the physical factors critical to an enterprise also need to be
monitored. For example, limits need to be set on how much pasture loss can be accepted before
some action must be taken to protect them. Factors to consider include-
 percentage of groundcover,
 species change and weed percentage per paddock, and
 dry matter produced in kg/ha.
4. Formulation of an action plan. The most difficult decisions involve livestock. Cropping tends to
have more yes/no decisions, but in stock management there is a wide range of options. The most
sensitive and the most forgiving areas under drought management practices need to be identified.
These will include-
 areas to be protected from stock,
 areas where stock can be fed,
 areas that need additional fences or watering points,
 priority areas for pest and weed control, including unwanted grazing by native animals,

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 which classes of stock to sell, and
 whether to sell or agist stock.
Floods
Floods cause losses to stock and damage crops, pastures, and road and rail links. They also often
put at risk the lives and economic well-being of rural communities. A flood management strategy
should include the following elements:
An identification of flood-prone land and the flooding history of the area
• An understanding of flood warnings and from where the flood patterns come
• Paddock and fence design to allow easy movement of stock, so that stock will not be trapped
in floods
• “All weather” access tracks where possible
• An arrangement for fodder storage that is always accessible
• A flood evacuation plan that includes the relocation of stock and equipment
• Farm infrastructure checks, for example, the switching off of electrical supplies to buildings
that may be flooded.
Climate Variability and Climate Change
Climate variability refers to variability observed in the climate record in periods when the state of
the climate system is not showing changes. If the climate state changes, usually characterized by
a shift in means, then the frequency of formerly rare events on the side to which the mean has
shifted might occur more frequently with increasing climate variability (Salinger, Stigter, and
Dasc, 2000).
Climate change is a movement in the climate system because of internal changes within the
climate system or in the interaction of its components, or because of changes in external forcing
either by natural factors or anthropogenic activities (International Panel on Climate Change
[IPCC], 1996).

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Probable Causes of Climate Variability and Climate Change:
External Causes
Astronomical periodicities: Many investigators of climate variability and change are of the
opinion that astronomical periodicities influence the atmosphere directly or indirectly and bring
periodic variations in climate. The most important periodicity is associated with the tidal forces of
the sun, moon, and other planets (Munk, Dzieciuch, and Jayne, 2002). The time scale of many of
the astronomical periodicities influencing the atmosphere cannot be demonstrated with certainty.
However, it is widely accepted that they have a relationship with the sequence of ice ages and the
intervening warmer and colder periods.
Sunspot cycle: The main known external causes of interannual climate variability and climate
change are changes in solar output. The variation in solar output coincides with the most prominent
and best-known solar disturbance of 11.08-year intervals, known as the sun spot cycle. Annual
numbers of sunspots have been recorded for many years by astronomers, and these show the
relative absence of sunspots from 1650 to 1700, the “Maunder minimum,” with a slight decrease
in solar output (Eddy, 1976). This minimum has been used by some to explain the Little Ice Age
(1430-1850) in Europe. Estimates place the increase in solar irradiance between the Maunder
minimum and now between 0.5 and 1.4 W m–2, or an increase of 0.3 percent of the solar irradiance
(IPCC, 1996).
Internal Causes
Greenhouse gases: Within the atmosphere there are naturally occurring greenhouse gases which
trap some of the outgoing infrared radiation emitted by the earth and the atmosphere. The principal
greenhouse gas is water vapor. The others are carbon dioxide (CO2), ozone (O3), methane (CH4),
and nitrous oxides (N2O). These gases, together with clouds, keep the earth’s surface and
troposphere warmer than it would be otherwise. This is the natural greenhouse effect. Changes in
the concentrations of these greenhouse gases will change the efficiency with which the earth cools
to space. The atmosphere absorbs more of the outgoing terrestrial radiation from the surface when

36
concentrations of greenhouse gas increase. This is the enhanced greenhouse effect—an
enhancement of an effect that has operated in the earth’s atmosphere for billions of years due to
naturally occurring greenhouse gases (IPCC, 1996).
Human activities are changing the concentrations and distributions of greenhouse gases and
aerosols in the atmosphere. The main human activities causing an increase in greenhouse gases are
the combustion of fossil fuels and deforestation by forest burning. According to the IPCC (1996),
global mean surface temperatures increased by 0.6°C since the late nineteenth century due to
anthropogenic causes.
Volcanic aerosols: Volcanic activity can inject large amounts of sulfur containing gases (primarily
sulfur dioxide) into the stratosphere. Once reaching the stratosphere, some gases rapidly oxidize
to sulfuric acid and condense with water to form an aerosol haze. Volcanic aerosols increase the
planetary albedo, and the dominant radiative effect is an increase in scattering of solar radiation,
which reduces the net radiation available to the surface/troposphere, thereby leading to a cooling.
This can produce a large but transitory negative radiative forcing, tending to cool the earth’s
surface and troposphere for periods of up to two to three years. To have global effects, the latitude
of eruption must lie between 30°N and 30°S. Eruptions poleward of these latitudes will affect the
hemisphere only where the eruption occurs (IPCC, 1996). Because the impacts of volcanic aerosols
last only a few seasons they increase the variability due to other effects.
The cryosphere: The changes in global snow and ice cover, other than in clouds, operate on long
time scales except for seasonal snow cover. Monitoring of seasonal snow cover since 1972 shows
that the extent of Northern Hemisphere snow cover has been less since 1987, particularly in spring
(WMO, 1998). This might have decreased the regional surface albedo with a consequent
temperature increase in the winter period for high latitude areas of the Northern Hemisphere
(Sirotenko, 1999).
Land surface changes: Land surface changes, particularly large-scale afforestation or
deforestation of areas, will affect the regional albedo and aerodynamic roughness. These will affect
the transfer of energy, water, and other materials within the climate system. These effects are often
more regional in their impacts on climate in the planetary boundary layer.

37
Apart from these, there are El Nino, La Nina, Southern Oscillation, Arctic Oscillation and other
internal dynamics/variations responsible for climate change.
Observed Impact of Climate Change
An accumulating body of evidence indicates that global warming (0.7°C over the twentieth
century), especially during the last 50 years (0.43°C), has impacted a number of regions. The rates
and patterns of climate change and impacts vary over the period as well. Anthropogenic and non-
anthropogenic changes may have influenced greater changes in the climate system later in the
century than earlier in the period. Impacts observed so far are primarily ecological in nature. These
include changes in physiology, spatial distribution, species abundance and diversity, and timing of
reproduction.
Much of the evidence of ecosystem changes to date has come from highlatitude (>40°N, 40°S) and
high-altitude (>3,000 m) environments, and from species at their high-latitude range limits. Some
evidence has been found in tropical and subtropical regions (both terrestrial and coastal
ecosystems) and some in temperate oceans and coastal areas.
Hydrology/Water Resource
Observations in 1995-1996 show declines of glacier extent in western Antarctica and elsewhere,
sea ice 40 percent thinner than 20 to 40 years ago in the Arctic, and shrinking of the area of
perennial Arctic ice at a rate of 7 percent per decade (Vaughan et al., 1999). Satellite data over
Northern Hemisphere extratropical lands show a retreat (about 10 percent reduction) of spring
snow cover over the period 1973 to 1992 (Groisman, Karl, and Knight, 1994). Glaciers in Latin
America have dramatically receded in the past decades. Many of them have disappeared
completely. In 18 Peruvian glacial cordilleras, mass balances since 1968 and satellite images show
a reduction of more than 20 percent of the glacial surface.
Changes in volume and areal extent of tropical mountain glaciers are among the best indicators of
climate change. Himalayan glaciers that feed the Ganges River appear to be retreating at a fast

38
rate. The estimated annual retreat of the Dokriani glacier (one of the several hundred glaciers that
feed the Ganges) in 1998 was 20 meters compared to an annual average of 16.5 meters over 1993
to 1998. From observations dating back to 1842, the rate of recession of the snout (the point at
which the glacier ice ends) has been found to have increased more than 2.5-fold per year. Between
1842 and 1935, the 26-kilometer long Gangotri glacier was receding at an average of 7.3 m every
year, whereas between 1935 and 1990, the rate of recession had gone up to 18 m a year. Almost
67 percent of glaciers in the Himalayan and Tienshan mountain ranges have retreated since the
1970s (Fushimi, 1999).
Vegetation
Increased temperatures in mountainous regions appear to be causing plant species to move to
higher altitudes. Approximate moving rates for common alpine plants are calculated to be between
zero and four meters per decade (Grabberr, Gottfried, and Pauli, 1995). In a short grass steppe in
Colorado, with recorded temperature increases from 1964 to 1998, aboveground net primary
productivity of the dominant grass is on the decrease (U.S. National Assessment, 2000).
Animals/Livestock
A northward and upward shift has been detected in the range of checker spot butterfly on the
western coast of North America over the past century. In a sample of 35 no migratory European
butterflies, 63 percent have ranges that have shifted north by 35 to 240 km during this century
(Parmesan et al., 1999). The disappearance of 20 out of 50 species of frogs and toads in Costa Rica
has been linked to recent warming (Pounds, Fogden, and Campbell, 1999). Earlier egg-laying dates
have been found for 31 percent of 225 species of birds in the United Kingdom over the period
1971 to 1995 (Crick et al., 1997). In the Netherlands, the availability of caterpillar food has
advanced by nine days over the period 1973 to 1995 (Visser et al., 1998). In marine and littoral
ecosystems, there is evidence of coral bleaching, declines of plankton, fish, and bird populations
related to warming ocean temperature, mangrove retreat due to sea-level rise, and penguin species
increases due to a decrease in sea ice. Between 1974 and 1993, species richness of reef fishes has

39
fallen and composition shifted from dominance by northern to southern species in the Southern
California Bight (Holbrook, Schmitt, and Stephens, 1997).
Agriculture
Agriculture evidence of observed impacts is found in lengthening growing seasons at high
latitudes, changing yield trends, and expansion of pest ranges. Carter (1998) observed that the
growing season of the Nordic region (Iceland, Denmark, Norway, Sweden, and Finland) has
lengthened over the period 1890 to 1995. Climate trends appear to be responsible for 30 to 50
percent of the observed increase in Australian wheat yields, with increases in minimum
temperatures (decreases in frosts) being the dominant influence during 1952 to 1992 (Nicholls,
1997). Recent movement of agricultural pests and pathogens related to local climate trends is
linked to global warming.
Problems and Prospects of Agriculture
Problems:
1. Primitive Type of Cultivation: The cultivators are still using almost all the age old appliances
like ploughs, yokes, harrows, weak bulls etc. for cultivation of their land which were used during
the ancient time. The development countries brought revolutionary changes in agriculture by using
modern and scientific equipment and other inputs like power tillers/ tractors, pesticides, fertilizer
etc. Japan, the Philippines, South Korea and the United States of America (USA) are more
advanced in this regard. Yield per acre in these countries is much higher than that of ours.
2. Diminishing Fertility of the Soil: Like all other elements, the soil has also a definite limit of
productivity or productive capacity. It is, therefore, necessary to raise the fertility of land for
increasing productive capacity by applying manures suitable for environment and this can be done
by mixing soil. Since the Bangladeshi cultivators are inexperienced in this regard, land of the rural
villages started diminishing its fertility.

40
3. Small Holding of Land: Due to increased population, joint families are gradually disappearing
and this is responsible for making the large holding smaller. Cultivation in such smallholdings is
not possible even by wooden plough.
4. Landless Cultivators: The rural poor people are day by day becoming landless due to economic
pressure. These landless people for their subsistence cultivate lands of the village ‘mahajans’ on
crop sharing basis. For want of ownership of land, they do not feel interested to properly invest;
even feel unwilling to render their physical labor on this land. For this reason, good harvest is not
possible.
5. Decreasing Per capita Cultivable Land: Cultivable land is being gradually reduced for
distribution of limited land among the increasing population of the country. It is learnt from the
meeting of the Parliamentary Committee of the Ministry of Agriculture held in September, 2003
that 82,900 hectares (i.e., about 1 percent) land is decreased per annum. Total cropped acreage is
shrinking from 35.07 million acres in 2001-02 to 33.92 million acres in 2006-07.
6. Cultivation for Livelihood: Most of the farmers of Bangladesh produce crops for livelihood
only; they had little interest for crop production on commercial basis. The commercial attitude for
production of crops has not yet been popular.
7. Dependence on Nature: Agriculture in Bangladesh depends on nature. Agricultural crop
production is seriously hampered every year by the vagaries of nature. There is a common word
that agriculture in Bangladesh is a gamble in the monsoons. But recently scientific method of
cultivation has been introduced in agriculture. Power tillers, irrigation technology, bio and
chemical fertilizer, insecticides etc. have also been widely used. As a result crop production varies
considerably.
8. Fallow Land: Vast land of the eastern region especially in the districts of Mymensingh,
Netrokona, Kishorganj, sylhet, Sunamganj etc. is still lying fallow and as such we are getting no
yield from those lands. In some cases these are not even possible to take under agriculture or pisi-
culture. This is essential to recover these lands and bring under cultivation.
9. Uneven Land: Natural composition of the land of eastern 3 zone like that of Mymensingh,
Sylhet, Chittagong and Dhaka is slightly uneven and for this reason most of these land cannot be

41
brought under irrigation facilities. The uneven land also cannot hold or contain water and therefore,
per acre yield of such lands is less than that of plain ones.
10. Lack of Marketing of Agricultural Produce: Agricultural product needs extensive marketing
program. It has not yet been possible to take extensive measures for making agriculture an industry
in villages.
11. Others:
 Population growth rate1.48%
 Climate change and variations
 Rapid urbanization growth @12%
 Agricultural research and education (manpower shortage, updating course curriculum)
 Technology generation (needs expertise, time and money)
 Technology dissemination (needs expertise, time, logistics support)
 Alternate livelihoods/rehabilitation program
 Inadequate value addition /food processing
 limate change adaptation & mitigation
 Developing stress tolerant varieties
 Transferring updated information and technologies to the field
 Attaining irrigation efficiency
 Regaining soil fertility and natural ingredients
 Research-extension-farmer-market linkage
 Shortage of Agril labour at peak seasons
Prospects:
1. Food for Human beings: It provides food that can be consumed by human beings. These include
vegetables, fruits and meat.
2. Food for Animals: Animals also feed on food grown through agriculture for instance hay,
fodder, silage and more.

42
3. Source of Livelihood: Many people spend their lives engaging in agriculture.They include
farmers, agronomists, transporters and many others.
4. Source of Income: People earn their living directly or indirectly though agriculture.
5. Raw Materials: Agriculture produces raw materials that are needed in manufacturing. Examples
include, sisal, cotton, bamboo and more.
6. Food Security: Agriculture is practiced to improve food security in a country.
7. Trading Commodity: Products such as wheat, corn, or tea are used as trading commodities in
the financial markets.
8. International Trade: International trade is dependent on agricultural products which are
interchanged between countries.
9. Foreign Exchange: Agricultural countries earn foreign currency by exporting agricultural
produce.
10. National Revenue: Many governments especially in developing countries earn most of their
income from agriculture.
11. Employment Opportunities: The agricultural sector is a leading employer in many countries.
12. Economic Development: Most countries and regions have experienced economic growth and
development because of agriculture.
13. Conserving the Environment: Good agricultural practices help in conserving the environment
and reducing pollution.
14. Transport Sector: The transport sector is heavily dependent on the agricultural sector.
15. Conducive Environment: Agriculture has transformed arid and semi-arid areas into green and
more conducive environments.
16. Forging International Cooperation: Many countries interact with each other because of
exporting and importing agricultural produce.
17. Improving Standards of Living: Good agricultural techniques help farmers and other players
improve their living standards.
18. Agro-Based Industries: Many industries crop-up to produce products that depend on cotton,
sisal, jute and other agricultural products.

43
19. Greener Environment: Agriculture can help enhance the surrounding by creating natural
vegetation instead of bare soil and rocks.
20. Support Scientific Research: Researchers and scientists normally rely on plants and animals
that have been produced through agriculture.
21. Improved Health: Most of the drugs and medication comes from produce that is farmed.
22. Water Conservation: Modern agriculture which relies on drip irrigation helps to conserve
water. Dams also stop water from wasting away.
23. Minimizing Pollution: Plants help purify the air by absorbing carbon dioxide and releasing
oxygen. The also trap harmful toxins and pathogens in the air.
24. Improving Soil Structure: The roots of plants hold together the soil particles and stop soil
erosion.
25. Absorb Heat: The vegetative cover helps cool the earth’s surface and reduces evaporation of
water from the surface.
26. Others (Bangladesh Context):
 Scope for expanding hybrid technology exists (10%)
 Prospects for adoption of advanced technology in agriculture are bright
 Potentials for proper utilization of hilly/coastal areas including agro-ecologically
disadvantaged regions exist
 Export potentials exist for high-value crops
 Scope for crop diversification, intensification and value addition to agricultural produces
 Agriculture sector has capacity to absorb labor force and to generate income.
Agro-Ecological Zone
Concept of Agro-ecological Zone
Agroecological Zone land areas recognised on the basis of hydrology, physiography, soil types,
tidal activity, cropping patterns, and seasons. In fact an agroecological zone indicates an area
characterized by homogeneous agricultural and ecological characteristics. This homogeneity is
more prominent in the sub region and unit levels.

44
The Agroecological Zones (AEZ) database is unique and is being extensively used for national
and local level production planning purposes. The agroecological resources are increasingly
playing an important role in agricultural planning, technology transfer and specific bio-physical
resource utilisation programme activities. The database on AEZ, however, needs updating as over
time there have been some changes in the land types because of roads and other structural
measures, variability in precipitation and temperature as well as innovation of modern crop
cultivation which could survive under different environmental stress conditions.
The agroecological zones of Bangladesh have been identified on the basis of four elements such
as physiography, soils, and land levels in relation to flooding and agro climatology. Bangladesh
has been tentatively divided into 30 agroecological zones. These 30 zones have been subdivided
into 88 agroecological sub-regions, which have been further subdivided into 535 agroecological
units.
Element and Nature of Agro-ecological Zones of Bangladesh
Physiography forms the primary element in defining and delineating the agroecological regions in
Bangladesh. Soils form the second element in defining and differentiating agroecological zones as
soil conditions determine important properties for plant growth, moisture supply, root aeration and
nutrient supply. The third factor is land level in relation to flooding. In this regard the country has
been classified into following types of land level such as-
i. Highland (land which is above normal flood-level)
ii. Medium highland (land which normally is flooded up to about 90 cm deep during the flood
season)
iii. Medium lowland (land which normally is flooded up to between 90 cm and 180 cm deep
during the flood season)
iv. Lowland (land which normally is flooded up to between 180 cm and 300 cm deep during
the flood season)
v. Very lowland (land which normally is flooded deeper than 300 cm during the flood season).

45
Agro-ecological Zones of Bangladesh
Agroecological zones are land areas recognised on the basis of hydrology, physiography, soil
types, tidal activity, cropping patterns, and seasons.
1. Old Himalayan Piedmont Plain
2. Active Tista Floodplain
3. Tista Meander Floodplain
4. Karatoya-Bangali Floodplain
5. Lower Atrai Basin
6. Lower Punarbhaba Floodplain
7. Active Brahmaputra-Jamuna Floodplain
8. Young Brahmaputra-Jamuna Floodplain
9. Old Brahmaputra Floodplain
10. Active Ganges Floodplain
11. High Ganges River Floodplain
12. Low Ganges River Floodplain
13. Ganges Tidal Floodplain
14. Gopalganj-Khulna Beels
15. Arial Beel

46
16. Middle Meghna River Floodplain
17. Lower Meghna River Floodplain
18. Young Meghna Estuarine Floodplain
19. Old Meghna Estuarine Floodplain
20. Eastern Surma-Kushiyara Floodplain
21. Sylhet Basin
22. Northern and Eastern Piedmont Plain
23. Chittagong Coastal Plain
24. St Martin’s Coral Island
25. Level Barind Tract
26. High Barind Tract
27. North-eastern Barind Tract
28. Madhupur Tract
29. Northern and Eastern Hills
30. Akhaura Terrace
Geographical Distribution of the Major Crops of Bangladesh
Major Crops: Crops that are grown on one percent or more of the gross-cropped area (GCA) of a
country. In Bangladesh, only nine crops- rice (73.94%), wheat (4.45%), jute (3.91%), rape and
mustard (3.08%), lentil (1.54%), chicklling vetch (1.25%), potato (1.13%), sugarcane (1.12%),
and chilli (1.05%) are grown on 1 percent or more of the crop acreage (14.61 million ha) and may
be considered as major crops (Source: Banglapedia).
Rice dominates the cropping pattern throughout Bangladesh. It has been broadly divided into three
classes viz, aman (transplanted and broadcast varieties), boro, and aush according to the season in
which they are harvested, namely, in December-January, March-May and July-August
respectively. Again, of these varieties transplanted aman is the most important and covers about
46.30% of the paddy area, followed by boro (26.85%), aus (17.59%) and broadcast aman (9.26%).

47
Transplanted aman is grown almost everywhere in Bangladesh, while broadcast aman is mostly
grown in the low-lying areas of the south and northeast. Boro is grown to a certain extent in every
district, especially in the irrigated part, while aus is a well scattered crop.
Wheat is the most important crop in Bangladesh next to rice. It is grown mainly in the drier parts
of the north and is cultivated only as a winter crop. Jute leads the country's list of export crops but
is ranked third in terms of area cultivated. It is confined mainly to the low-lying areas of the
Brahmaputra-Jamuna and Padma floodplains.
Mustard (including rape) is the fourth important crop. It
is also grown mainly in the low-lying areas of
Brahmaputra-Jamuna and Meghna floodplains.
Masur (lentil) and khesari (chickling vetch) are the two
important varieties of pulses produced in Bangladesh.
Masur is mainly grown in the Gangetic delta while
khesari is a well-scattered crop in the islands and chars
(any accretion in the riverbed, usually sandy islands).
Potato is the most important of the winter vegetables
and is widely grown. At present potato is a most
important crop to Munshiganj, Comilla, Rajshahi,
Rangpur, Dinajpur, Bogra, Joypurhat and Nilphamari
districts. Sugarcane is the eighth important crop the
country. It grows best in Rajshahi, Natore, and
Chuadanga districts.
Chilli is produced although to a certain extent in every
district of the country, the cultivation is mainly
concentrated in the southern districts including Bogra,
Sirajganj and Pabna.

48
Plausible Impact of Climate Change on Agriculture of Bangladesh
Agriculture is the most vulnerable sector as its productivity totally depends on climatic factors like
temperature, rainfall, light intensity, radiation and sunshine duration, which are predicted to be
erratic. Incidences of floods, droughts, high temperature, flash floods and floods, etc., are predicted
to be more frequent and intense. Salinity intuition could be more acute problem in future due to
sea level rise.
Impact of Temperature on Crop Production
Every crop has a temperature range for their vegetative and reproductive growth. When
temperature falls below the range or exceeded the upper limit then crop production faces
constraints. A study found that 10C increase in maximum temperature at vegetative, reproductive
and ripening stages there was a decrease in Aman rice production by 2.94, 53.06 and 17.28 tons
respectively. With the change in temperature (by 20C and 40C), the prospect of growing wheat
and potato would be severely impaired. Production loss may exceed 60% of the achievable yields.
Higher temperature has negative effect on soil organic matter also.
Impact of Rainfall on Crop Production of Bangladesh
Rainfall is one of the major climatic factors for crop production. All crops have critical stages
when it needs water for their growth and development. Moreover excessive rainfall may occur
flooding and water logging condition that also lead to crop loss. It was found that 1mm increase
in rainfall at vegetative, reproductive and ripening stages decreased Aman rice production by
0.036, 0.230 and 0.292 ton respectively. Scarcity of water limits crop production while irrigation
coverage is only 56% as delivered by the Bangladesh Agriculture Development Corporation
(BADC).
Impact of Sea Level Rise on Crop Production
Sea level rise affects agriculture in three ways, i.e., by salinity intrusion, by flooding and by
increasing cyclone frequency and its depth of damage. Combined effects of these three factors

49
decrease agriculture production in the coastal zone. Salinity intrusion due to sea level rise will
decrease agricultural production by unavailability of fresh water and soil degradation. Salinity
also decreases the terminative energy and germination rate of some plants. The loss of rice
production in a village of Satkhira district was investigated and it was found that rice production
in 2003 was 1,151 metric tons less than the year 1985, corresponding to a loss of 69%. Out of the
total decreased production, 77% was due to conversion of rice field into shrimp pond and 23%
was because of yield loss. Sea level rise cause inundation of more area which is already reported
by scientist. Therefore damage of agricultural crops will be more in future. About 1/3 of
Bangladesh or 49,000 sq. km. area are influenced by tides in the Bay of Bengal. Through study it
is clear that the inundation coastal inundation area will be increased in future with an adverse effect
on crop production. In a study found that if sea level rise up to 1 meter, normal flood waves can
be expected to increase from presently 7.4 meters to 9.1 meters. In Bangladesh, about 15-17
million people will be displaced from the land inundation by sea level rise that will cost 12-16%
of total land area.
Impact of Flood on Crop Production
Flood has most deleterious effect on crop production of Bangladesh. The 1988 flood caused
reduction of agricultural production by 45%. Higher discharge and low drainage capacity, in
combination with increased backwater effects, would increase the frequency of such devastating
floods under climate change scenarios. Prolonged floods would tend to delay Aman plantation,
resulting in significant loss of potential Aman production, as observed during the floods of 1998.
Loss of Boro rice crop from flash floods has become a regular phenomenon in the haor areas over
the recent years. Considering all the direct and induced adverse effects of climate change on
agriculture, one may conclude that crop agriculture would be even more vulnerable in Bangladesh
in warmer world.

50
Impact of Cyclone on Crop Production
Cyclone cause huge damage to production of crop. FAO/GIEWS Global Watch (2007) reported at
the time of the passage of cyclone SIDR, the main 2007 “aman” rice crop, accounting for about
70% of the annual production in the most affected area, was nearing harvest. According to the
estimate by Department of Agricultural Extension of Bangladesh, the loss in rice equivalent is at
some 1.23 million tonnes, with 535,707 tonnes in the four severely affected districts, 555,997
tonnes in badly affected 9 districts and 203,600 tonnes in moderately affected 17 districts in
Bangladesh.
Impact of Drought on Crop Production Due to Climate Change
Drought mostly affects Bangladesh in pre-monsoon and post-monsoon periods. During the last 50
years, Bangladesh suffered about 20 drought conditions. During 1981 and 1982 droughts affected
the production of the monsoon crops only. The drought condition in north-western Bangladesh in
recent decades had led to a shortfall of rice production of 3.5 million tons in the 1990s. If other
losses, such as, to other crops (all rabi crops, Sugarcane, Tobacco, Wheat etc.) as well as to
perennial agricultural resources, such as, bamboo, betel nut, fruits like Litchi, Mango, Jackfruit,
Banana etc are considered, the loss will be substantially much higher.
Thermoperiodism
The response of living organisms to regular changes in temperatures, either day/night or seasonal,
is known as thermoperiodism. Thermoperiodism exerts effects on the seasonal biology of insects
and the growth and development of plants. Effects on insects include rates of growth and
development, determination of diapause and dormancy, and acclimatization to low temperatures.
Effects on growth and development of plants vary from one species to another. Crops such as
soybean, maize, tomato, potato, eucalyptus, and mango are classified as thermoperiodic, while
wheat, oats, peas, and cucumber are classified as nonthermoperiodic.
In soybean, a cool day/night temperature combination of 18/14°C disrupts floral development,
leading to physically malformed parts. Normal floral initiation and pod development occurs at

51
30/18°C and 30/22°C, respectively, while the greatest number of pods per plant is obtained at
26/14°C (Judith and Raper, 1981). Tomatoes grow faster when the temperature is 26°C by day and
17°C by night than at the constant temperature of 26°C or any intermediate temperature. For this
reason, tomatoes do not grow well in warm countries except in those locations where the
temperature falls appreciably at night.
Some maize cultivars respond to a daily temperature fluctuation. In experiments with three lines
differing in earliness (early, mid, and late) grown in a phytotron from two-week-old seedlings
raised in a 16 h photoperiod under three different day/night temperature regimes, there was a direct
corre lation between chlorophyll content and grain yield. It proved best for yield and energy
savings to raise seedlings of early lines at a high diurnal temperature (day/night = 24/15°C), and
midseason or late lines at a constant day and night temperature of 21°C (Stolyarenko et al., 1992).
Potato plants grown under the fluctuating temperature treatment develop normally, develop tubers,
and have a fivefold or greater total dry weight compared to those under constant temperature. This
suggests a thermoperiod could allow normal plant growth and tuberization in potato cultivars that
are unable to develop effectively under continuous radiation (Tibbitts, Bennet, and Cao, 1990).
The ecological significance of this response to a diurnal alteration of temperature may be that it
promotes germination of those seeds close to the soil surface. When such fluctuations do not occur,
germination, especially of more deeply seated seeds, may remain suppressed.
Apart from daily fluctuations in temperature, seasonal fluctuations are important in the
development of many plants. Annual plants do not need a cold period during their development,
except for plants that germinate in autumn and flower in the spring or summer after a cold winter.
An example is winter wheat. Peaches cannot flower at high temperatures, but the vegetative growth
phase continues. They need a period of cold weather before flower buds can open. No flower
primordia are laid down under conditions of continued high temperature.
Irrigation efficiency
Irrigation efficiency expresses the performance of a complete irrigation system or components of
the system. Irrigation efficiency is defined as the ratio between the amount of water used to meet

52
the consumptive use requirement of crop plus that necessary to maintain a favorable salt balance
in the crop root zone to the total volume of water diverted, stored or pumped for irrigation. Thus,
water applied by the irrigation system and not being made available to be taken up by plant roots
is wasted and reduces irrigation efficiency.
Irrigation efficiency in Bangladesh: In Bangladesh, about 94% of the irrigated land is under small
and minor irrigation. But sub-optimal use of these irrigation devices and unplanned cropping
activities have resulted in low irrigation coverage. The irrigation efficiency is only about 30%.
With proper utilization and improved management, 4.0 to 5.0 million ha of land can be irrigated
easily by using the same number of irrigation devices instead of the present 3.12 million ha.
Efficient Use of Water in Irrigation for demand management:
The limited water resources make it necessary to undertake all necessary measures for efficient
irrigation systems, taking into account the increase in production and water consumption savings,
and also allow the cultivation of larger areas, even in years of water shortage, and this requires the
following:
 The introduction of best technologies and modern and advanced irrigation systems in terms
of the efficient water use in agriculture.
 Adopt preventive maintenance programs for irrigation systems, which lead to sustain
efficient water use and reduce losses. Irrigation water use and efficiency (on-farm,
conveyance, and distribution) should be regularly monitored for demand forecasting and
planning purposes.
 Appropriate programs and procedures should be adopted, to ensure uniform flow discharge
and stable pressure all through the irrigation networks.
Desertification
 According to Princeton University Dictionary- Desertification is a process of transforming
fertile land into deserts due to drought, deforestation and inappropriate agriculture.

53
 According to Oxford Dictionary of Geography- Desertification refers to the spread of desert
like condition of semi-arid environment.
Desertification Facts:
 Dry land covers 41-42% of the total land of the world (Baurer, 2007).
 2 billion inhabitants are on the dry lands (Johnson et al., 2006).
 6-12 million sqkm is affected by desertification and 1 billion inhabitants are at the risk (Holtz,
2007).
Causes of Desertification: In general-
1. Drought
2. Deforestation/ vegetation cover loss
3. Overgrazing
4. Inappropriate agriculture system
5. Climate change
6. Overpopulation
Expert driven-
According Dr. H. Dregne (1985) in the book Desertification of Arid Lands-
1. Degradation of vegetation cover
2. Water erosion
3. Wind erosion
4. Salinization
5. Reduction of organic matter
6. Excess of toxic substances
Stages of desertification:
1. Lessening the concentration of vegetation cover.

54
2. Origination of empty spaces among the vegetation covered area, the land looks like
stripe and the phenomenon is called as Tiger Fur Pattern.
3. Increases of empty spaces among the trees.
4. The empty spaces are prevailing over the previously green area.
Consequences:
The desertification leads to soil infertility, soil organic material and biodiversity loss, food
insecurity, sand storm and ultimate poverty of the region.
CropWat
CROPWAT is a decision support tool developed by the Land and Water Development Division of
FAO. CROPWAT (latest version is 8.0) for Windows is a computer program for the calculation
of crop water requirements and irrigation requirements based on soil, climate and crop data. In
addition, the program allows the development of irrigation schedules for different management
conditions and the calculation of scheme water supply for varying crop patterns. CROPWAT 8.0
can also be used to evaluate farmers’ irrigation practices and to estimate crop performance under
both rainfed and irrigated conditions.
Its basic functions include the calculation of reference evapotranspiration, crop water
requirements, and crop and scheme irrigation. Through a daily water balance, the user can simulate
various water supply conditions and estimate yield reductions and irrigation and rainfall
efficiencies. Typical applications of the water balance include the development of irrigation
schedules for various crops and various irrigation methods, the evaluation of irrigation practices,
as well as rainfed production and drought effects.
Calculation procedure
The calculation of reference evapotranspiration (ET o ) is based on the FAO Penman-Monteith
method (FAO, 1998). Input data include monthly and ten-daily for temperature (maximum and
minimum), humidity, sunshine, and wind-speed. Crop water requirements (ETcrop) over the

55
growing season are determined from ET o and estimates of crop evaporation rates, expressed as
crop coefficients (K c ), based on well-established procedures (FAO, 1977), according to the
following equation:
ETcrop = Kc × ETo
FAO (1998) has presented updated values for crop coefficients. Through estimates of effective
rainfall, crop irrigation requirements are calculated assuming optimal water supply. Inputs on the
cropping pattern will allow estimates of scheme irrigation requirements.
Millennium Development Goal and Sustainable Agriculture
The Millennium Development Goals (MDGs) were eight international development goals for the
year 2015 that had been established following the Millennium Summit of the United Nations in
2000, following the adoption of the United Nations Millennium Declaration. All 191 United
Nations member states at that time, and at least 22 international organizations, committed to help
achieve the following Millennium Development Goals by 2015:
1. To eradicate extreme poverty and hunger
2. To achieve universal primary education
3. To promote gender equality and empower women
4. To reduce child mortality
5. To improve maternal health
6. To combat HIV/AIDS, malaria, and other diseases
7. To ensure environmental sustainability
8. To develop a global partnership for development
Sustainable agriculture is farming in sustainable ways, which means meeting society's food and
textile present needs, without compromising the ability of future generations to meet their needs.
It can be based on an understanding of ecosystem services. There are many methods to increase
the sustainability of agriculture. When developing agriculture within sustainable food systems, it

56
is important to develop flexible business process and farming practices. The goals of sustainable
agriculture-
• Satisfy human food and fiber needs
• Enhance environmental quality and the natural resource base upon which the agriculture
economy depends
• Make the most efficient use of nonrenewable resources and on-farm resources and integrate,
where appropriate, natural biological cycles and controls
• Sustain the economic viability of farm operations
• Enhance the quality of life for farmers and society as a whole.
The first goal of the MDG is entirely dependent on agricultural sustainability and so are the rest
somehow directly or indirectly.
Recent Agricultural Trend of Bangladesh
According to Bangladesh Economic Update (2016)-
Ensuring food security for the vast population of Bangladesh is directly associated with the
agricultural development in the country. The governments of Bangladesh have therefore been
giving priorities to agricultural development with a view to ensuring food and nutritional security,
poverty alleviation, and increased generation of employment. Whereas a profitable, sustainable,
and environment-friendly agricultural system is required to achieve these objectives, agriculture
in the country faces by a number of challenges every year. These challenges include population
growth, climatic hazards, loss of arable land, lack of quality seeds, food habit of people (about 90
percent is rice based), inadequate credit support to the farmers, unfair pricing, insufficient
investment in agricultural research and agricultural mismanagement in terms of irrigation, use of
fertiliser and pesticides. The majority are small and marginal farmers who are endowed with poor
financial resources and cannot afford high cost of frontier technology.
A declining trend in the growth of agricultural sector has recently been noticed, which, in turn,
contributed to decelerating growth in GDP in the country. Though there was an increasing trend

57
in growth in agriculture from 1990 to 2010, since the FY2010-11 the rate of growth has been
falling. The rate of growth in agriculture declined to 3.04 percent in FY 2014-15 from 4.37 percent
in FY 2013-14, representing 1.33 percentage points decrease. The rate of growth in agriculture
was 5.24 percent in FY2009- 10, whereas in FY2010-11, FY2011-12 and FY2012-13 the
ratewas5.13 percent, 3.11 percent and 2.17 percent respectively. This falling growth in agriculture
has been causing the share of agriculture in GDP to decline over the recent years. For instance, in
FY2009-10, the share of agriculture in GDP was 20.29 percent, whereas in FY2010-11, FY2011-
12 and FY2012- 13the share was 20.01 percent, 19.42 percent and 18.70 percent respectively. As
a result of this declining contribution of agriculture to national income, the growth of GDP in the
country has also been found decelerating. If the current trend persists, the agricultural growth rate
might reach as low as 2.09 percent in FY 2013-14.
Recent declining trend of growth in agriculture
can be attributed to a number of reasons. First,
the post-green revolution period has not
experienced any breakthrough as regards
technological advancement in the country on the
one hand, and the poor and marginal farmers who
comprise the majority of total farm population
cannot afford the high cost of using high input technologies in agriculture on the other. Second,
despite higher cropping intensity, the declining trend in the availability of arable land causes the
growth in agricultural sector to fall. Third, though the budget allocation in agriculture is increasing,
the large portion of this allocation goes for meeting non-development expenditure every year
leaving a meager amount for development spending, thus constraining development in the sector.
For instance, 85 percent of total agriculture-related budget was allocated for meeting non-
development expenditure in FY2009-10, 84 percent in FY2010-11 and 85 percent in FY2011-12.
Therefore, in order to raise productivity and profitability, reduce instability, and increase efficiency
in resource use, increase of the allocation on the development side is important.

Agroclimatology

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