Population forecasting methods
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The document discusses various methods for population forecasting to estimate future population for designing water supply and sanitation schemes. It describes the Arithmetic Increase Method, Geometric Increase Method, Incremental Increase Method, Decrease Rate of Increase Method, Simple Graphical Method, Comparative Graphical Method, Master Plan/Zoning Method, and Logistic Curve Method. Selection of the appropriate method depends on factors like the city size, growth pattern, and development stage. The objective is to forecast population accurately to ensure water systems are adequately sized but also cost-effective.
![Incremental increase method…
The advantages of both arithmetic increase method and geometrical
increase method are included in this method. Average increase per decade
is found out first of all and average percentage increase per decade is
worked out as in arithmetic increase method and geometric increase
method respectively.
Mathematically…….. Pņ=𝑃+𝑛𝑑+[(𝑛 /𝑛+1) /2]𝑡
Where,
Pņ = future population after n decades
P = present population
t = average incremental increase per decade
d = average increase in population per decade](https://image.slidesharecdn.com/populationforecasting-200810153117/85/Population-forecasting-methods-11-320.jpg)
Population forecasting methods
- 1. Population forecasting Mr. M. H. Mota Assistant professor SITCOE
- 2. Outcome: To estimate the future population using various methods of population forecasting
- 3. Some facts… • Water supply and sanitation is treated as a State subject as per the federal Constitution of India and, therefore, the States are provided with the constitutional right on the planning, implementation and cost recovery of water supply and sanitation projects. • The Public Health Engineering Department (PHED) is the principal agency at the State level for planning and implementation of water supply and sanitation programmes.
- 4. Some facts… • In a number of States, statutory Water Supply & Sanitation Boards (WSSBs) have taken over the functions of the PHEDs. The basic objectives for creation of WSSBs have been to bring in the concept of commercialization in the water supply and sanitation sector management and more accountability. • Such Boards have been set up in Assam, Bihar, Gujarat, Karnataka, Kerala, Maharashtra, Orissa, Punjab, Uttar Pradesh and Tamil Nadu. The metropolitan cities of Bangalore, Hyderabad and Chennai have separate statutory Boards.
- 5. • The objective of a public protected water supply is to supply safe and clean water in adequate quantity, conveniently and economically as possible. • The water to be handled may vary both in quantity and quality and the degree of treatment required, seasonally, monthly, daily and sometimes even hourly. • Water supply management aims to improve the supply by minimizing losses and wastage and unaccounted for water in the transmission mains and distribution system. • Water supply projects may be designed normally to meet the requirements over a thirty year project after their completion. the time lag between design and completion of the Project should also be taken in to account which should not exceed two to five years. Some facts…
- 6. • The design population will have to be estimated with due regard to all the factors governing the future growth and development of the area in the industrial, commercial, educational, social and administrative spheres, special factors causing sudden emigration or influx of population should also be foreseen to extent possible. • The judgment based on these factors would help in selecting the most suitable method of deriving the probable trend of the population growth in the area of the project.
- 7. Population forecasting… Design of water supply and sanitation scheme is based on the projected population of a particular city, estimated for the design period. Any underestimated value will make system inadequate for the purpose intended; similarly overestimated value will make it costly. Factors affecting changes in population are: increase due to births. decrease due to deaths. increase/ decrease due to migration. The present and past population record for the city can be obtained from the census population records. After collecting these population figures, the population at the end of design period is predicted using various methods as suitable for that city considering the growth pattern followed by the city.
- 8. Methods of population forecasting… Arithmetic Increase method Geometric Increase Method Incremental Increase Method Decrease Rate of Increase Method Simple Graphical Method Comparative Graphical Method The Master Plan Method or Zoning Method Logistic Curve method
- 9. Arithmetic increase method… Average rate of increase in population is assumed to be constant from decade to decade in this method. Average increase per decade is found out from the previously available census data. Mathematically…….. Pņ = P+nd Where….. Pņ = future population after n decades P = present population n = number of decades d = average increase per decade
- 10. Geometric increase method … Average percentage increase in population is assumed to be constant from decade to decade in this method. Averagepercentage increase per decade is found out from the previously available census data. By using the formula given below the future population is worked out. Mathematically…….. Pņ= P(1+r/100) 𝑛 Where, • Pņ= future population after n decades • P= present population • n= number of decades • r= average percentage increase per decade
- 11. Incremental increase method… The advantages of both arithmetic increase method and geometrical increase method are included in this method. Average increase per decade is found out first of all and average percentage increase per decade is worked out as in arithmetic increase method and geometric increase method respectively. Mathematically…….. Pņ=𝑃+𝑛𝑑+[(𝑛 /𝑛+1) /2]𝑡 Where, Pņ = future population after n decades P = present population t = average incremental increase per decade d = average increase in population per decade
- 12. Decrease Rate of Growth Method … It has been seen that all life grow within limited space. If the complete growth of a very old city is plotted, it will be seen that the curve has S- shape, which indicates that early growth takes place at an increasing rate, latter growth is at a decreasing rate which indicates that saturation limit is reached. In this method, the average decrease in the percentage increase is worked out and is then subtracted from the latest percentage increase for each successive decade.
- 13. Graphical Method… In this method, the populations of last few decades are correctly plotted to a suitable scale on graph. The population curve is smoothly extended for getting future population. This extension should be done carefully and it requires proper experience and judgment.
- 14. Comparative Graphical Method… • In this method the population data of project is plotted along with past population data of number of towns which have grown under the similar conditions. The curve of the city under consideration is extended carefully after studying the pattern of other cities.
- 15. The Master Plan Method or Zoning Method … The development of towns and cities is not allowed in haphazard way. For the development of the towns and cities, their master plans are prepared. The city is divided into various zones such as commercial centres, industrial areas, residential areas, the schools, colleges, parks etc. The future expansion of the cities is strictly regulated by various bylaws of corporations and other local bodies, according to the master plan. The master plans are prepared for the development of the cities for 25-30 years. The population densities for various zones of the towns to be developed are also fixed. Now when the population of a particular zone is fixed, it is very easy to design the water supply schemes for the particular zones. The future development of the water works is also designed on the basis of the master plan.
- 17. Logistic Curve method… • It is a modern method of the population forecasting where the population data of the past is analyzed critically by the software and the forecasting is done . Mathematically the solution is obtained using the relation as stated below… Formula: where Ps = Upper limit/saturation population Py=Population at starting P=Population at any time ‘t’ K= constant
- 18. Selection of the methods… Generally ‘Arithmetic Increase method’ is suitable for old and large city where the population growth is linear. Geometric Increase Method or ‘Incremental Increase Method’ is suitable for newly developing cities where the growth rate is more because of its growth pattern and large amount of increase is expected because of possible migration due to development. ‘Decrease Rate of Increase Method’ is suitable for a matured and well developed city which is approaching the saturation in terms of growth potential. Simple Graphical Method is suitable for developing towns where the development has a good potential to attract the people.
- 19. Comparative Graphical Method is suitable for the towns or cities which are showing the similar pattern in which the development of few towns has been observed. Logistic Curve method can be used for large cities where the generalization in any terms is difficult to state and all possible patterns has to be considered for forecasting of population.
- 20. Please remember….. Suitability of each method is to be determined critically. Care has to be taken while selecting any method for the forecasting in any given case. The trend of increase in the population shown by the city under consideration can be the most suitable way to take the decision to implement any method for forecasting the population.
- 22. That’s it for the session!!!! Lets meet in next session to learn more….