Download - Population Forecasting
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Population
forecasting
![Page 2: Population Forecasting](https://reader035.vdocuments.site/reader035/viewer/2022082209/5695d0801a28ab9b0292b230/html5/thumbnails/2.jpg)
Relation of Quantity of Water
and Population
Water consumption is influenced by the following
factors
Climate
Economic level
Population density
Degree of industrialization
Cost
Pressure
Quality of the supply
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Analysis of the future demand begins by
considering the present use
Consumption is classified according to;
Classes of users (domestic, commercial,
industrial, public, etc)
Area of the city
Economic level of the users
Season of the year
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On per capita consumption, applying the
procedure of dividing total use by the total
population should be applied with care, since
Entire population may not be served by the municipal
system
There may be large industrial users which will not
change with population
Characteristics and size of the population may be
changing
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Population estimation
Since population is always a relevant
factor in estimating future use, it is
necessary to predict what the future
population will be
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Arithmetic method
The assumption is that the rate of growth is
constant ๐๐
๐๐ก= ๐พ
where ๐๐
๐๐ก is the rate of change of population and
K is a constant
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The population in the future is estimated as; ๐๐ก = ๐๐ + ๐พ๐ก
where ๐๐ก is the population at some time in the
future, ๐๐ is the present population and t is the
period of the projection
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Geometric or Uniform Percentage Method
The hypothesis of geometric or uniform
percentage growth assumes a rate of
increase which is proportional to population
๐๐
๐๐ก= ๐พโฒ๐
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Geometric or Uniform Percentage Method
Thus, the population at some time is
estimated as; ๐๐๐ = ๐๐๐๐ + ๐พโฒโ๐ก
๐คโ๐๐๐ ๐พโฒ =ln (๐2) โ ln (๐1)
๐ก2 โ ๐ก1
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Curvilinear Method This technique involves the graphical projection of the
past population growth curve, continuing whatever
trends the historical data indicate
Includes comparison of the projected growth to the
recorded growth of other cities of larger size
Geographical proximity, likeness of economic base,
access to similar transportation systems, and other
factors should be considered for comparison
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Fig. Curvilinear method of projecting population growth
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Logistic Method
The logistic curve used in modeling
population growth has an S shape โ
combining a geometric rate of growth at low
population with a declining growth rate as the
city approaches some limiting population.
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In the short term, a logistic projection can be
based on
๐ =๐๐ ๐๐ก
1 + ๐๐+๐โ๐ก
where ๐๐ ๐๐ก is the saturation population of the
community and ๐ ๐๐๐ ๐ may be determined
from three successive census population
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๐๐ ๐๐ก =2๐๐๐1๐2 โ ๐1
2(๐๐ + ๐2)
๐๐๐2 โ ๐12
๐ = ๐๐๐๐ ๐๐ก โ ๐2
๐2
๐ =1
๐๐๐
๐๐(๐๐ ๐๐ก โ ๐1)
๐1(๐๐ ๐๐ก โ ๐๐)
where n is the time interval between succeeding censuses
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Declining Growth Method
Assumes that the city has some limiting
saturation population, and that its rate of
growth is a function of its population deficit; ๐๐
๐๐ก= ๐พ"(๐๐ ๐๐ก โ ๐)
๐พ" =1
๐๐๐
๐๐ ๐๐ก โ ๐1
๐๐ ๐๐ก โ ๐๐
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where ๐ ๐๐๐ ๐๐ re populations recorded in n
years apart
Future population can be estimated as;
๐ = ๐๐ + (๐๐ ๐๐ก โ ๐๐)(1 โ ๐๐พ"โ๐ก)
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Ratio Method
Relies on the population projections made by
professional demographers
Based on the assumption that the ratio of the
population of the city being studied to that of
the larger group will continue to change in the
future in the same manner that has occurred
in the past
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The ratio is calculated for a series of
censuses, the trend line is projected into the
future, and the projected ratio is multiplied by
the forecast regional population to obtain the
cityโs population in the year of interest
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Use of good judgement in population
estimation is important
If the estimate is too low, the system will be
inadequate and redesign, reconstruction and
refinancing will be necessary
Overestimation will result in excess capacity
which must be financed by a smaller
population at a higher unit cost
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Selection of an appropriate technique requires
testing all methods against recorded growth and
eliminate those which are not applicable
Growth of a community
with limited land area for future expansion may be
modeled by the declining growth or logistic technique
with large resources of land, power, and water and
good transportation may be predicted by the
geometric or uniform percentage growth
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Example:
Given the population data as follows;
Population in 2000 = 76.5million
2010 = 92.3milliom
Estimate the population in 2020, 2030, 2040
using the arithmetic, geometric, logistic and
declining growth methods