Smsn 03 Population Forecasting

7/23/2019 Smsn 03 Population Forecasting

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POPULATION FORECASTING

LECTURE 4



WATER SUPPLY

• Determination of population is one of the mostimportant factors in the planning of water supplyproject.

• Design period of the water supply project :20-40years

• The time lay between the design period and

completion should not be more than 2 years.



FLUCTUATIONS IN RATE OF DEMAND

• Average Daily Per Capita Demand = Quantity Required in 12

Months/ (365 x Population)If this average demand is supplied at all the times, it will not

be sufficient to meet the fluctuations.

• Seasonal variation: The demand peaks during summer.Firebreak outs are generally more in summer, increasing

demand. So, there is seasonal variation .

• Daily variation depends on the activity. People draw outmore water on Sundays and Festival days, thus increasing

demand on these days.



• Hourly variations are very important as they have a wide range. During

active household working hours i.e. from six to ten in the morning andfour to eight in the evening, the bulk of the daily requirement is taken.During other hours the requirement is negligible. Moreover, if a fire breaksout, a huge quantity of water is required to be supplied during shortduration, necessitating the need for a maximum rate of hourly supply.

So, an adequate quantity of water must be available to meet the peakdemand. To meet all the fluctuations, the supply pipes, service reservoirsand distribution pipes must be properly proportioned. The water issupplied by pumping directly and the pumps and distribution system mustbe designed to meet the peak demand. The effect of monthly variationinfluences the design of storage reservoirs and the hourly variationsinfluences the design of pumps and service reservoirs. As the population

decreases, the fluctuation rate increases.

FLUCTUATIONS IN RATE OF DEMAND




TECHNIQUE



POPUL TION GROW TH

Population growth rate: 1.312% (2012 est.)

Definition: The average annual percent change in the population,resulting from a surplus (or deficit) of births over deaths and the balance of

migrants entering and leaving a country. The rate may be positive ornegative. The growth rate is a factor in determining how great a burdenwould be imposed on a country by the changing needs of its people forinfrastructure (e.g., schools, hospitals, housing, roads), resources (e.g.,food, water, electricity), and jobs. Rapid population growth can be seen as

threatening by neighboring countries.



In order to predict the future population ascorectly as possible, it is necessary to knowthe factors responsible for changes inpopulation. They are:

BIRTH

DEATHS

MIGRATIONS



DEFINITIONS

• ESTIMATE

– “is an indirect measure of a present or pastcondition that can be directly measured.”

• PROJECTION (OR PREDICTION):

– “are calculations of future conditions that wouldexist as a result of adopting a set of underlyingassumptions.”

• FORECAST: – “is a judgmental statement of what the analyst

believes to be the most likely future.”



POPULATION OF INDIA -2011



HUMAN POPULATION



GROWTH CURVE

•

The population would probably follow the growthcurve characteristics of living things within

limited space or with limited economic

opportunity. The curve is S-shaped is known as

logistic curve.

• The represents early growth AB at an increasing

rate (i.e. geometric or log growth, p t ∞ P

and late growth DE at a decreasing rate (i.e. first

order curve p t

∞ (Ps - P )) as the saturation

value (Ps) is approached .

• The transitional middle curve BD follows an

arithimetic increase(i.e. p t = constant].

A

B

C

D




Analysts that undertake population forecasting have a wide variety of method

available to them, all with a mix of strengths and weaknesses.

-Simple extrapolation -Complex Ratio

-Complex extrapolation -Cohort Survival

-Simple Ratio -Cohort Component

The choice of projection method depends upon a number of factors.



FACTORS INFLUENCING THE CHOICE OF

FORECASTING METHOD

• Plausibility

• Face Validity depends on Availability and Quality of Data

• Resources includes Money, Personnel, Time

• Forecast Accuracy

• Model Complexity Ease of Application and Explanation

• Needs of the Users includes Geographic Detail

Demographic Detail

Temporal Detail

• Political Acceptability



FORECASTING ACCURACY

• In theory, the most important criteria for a forecast is its level

of accuracy. We assume that a forecast that is off by only 2%

is much better than one that is off by 20%.

• However, the likelihood of forecast accuracy serving as the

most important criteria in choosing a method depends on

local conditions.

• For example, sometimes politics plays a very important role in

the choice of a method and, by extension, the result

generated by a forecast



POPULATION PROJECTION



POPULATION FORECASTING TECHNIQUES

• ARITHMETIC INCREASE METHOD

• GEOMETRICAL INCREASE METHOD

• INCREMENTAL INCREASE METHOD

• DECREASING RATE METHOD

• SIMPLE GRAPHICAL METHOD



ARITHMETIC INCREASE METHOD

•

This method is based on upon the assumption that thepopulation increases at a constant rate; i.e.. The rate ofchange of population with time (i.e. dp/dt) is constant.

• Applicable to old and large cities with no industrialgrowth and reached a saturation or maximum

development.• This method yields lower results for rapidly growing

cities.

Pn = (P + n x)

Where , P= latest known population : Pn = prospective population after ‘n’ decades. x = average increase in population per decade.



GEOMETRIC INCREASE METHOD

•

In this method, the per decade percentage increase orpercentage growth rate (r) is assumed to be constant, and the

increase is compounded over the existing population every

decade. This method is, therefore, also known as uniform

increase method. It can be expressed as

Pn = P [1+ (r/100)]^n

Where , r= Geometric mean percentage increase.

• The basic difference between arithmetic and geometric

progression methods is: in former method no compounding is

done where as in latter method compounding is done in every

decade.

• The computation in two methods are thus comparable to

simple and compound interest computations respectively.



INCREMENTAL INCREASE METHOD

In this method, per decade growth rate is not assumedto be constant as in the arithimetic or geometric methods;but is progressively increasing or decreasing, dependingupon whether the average of the incremental increases inthe past data is positive or negative.

The population for a future decade is by adding the meanarithmetic increase ( say x )to the last known populationas in arithmetic increase method and to this is added the

average of the incremental increases y , once for the firstdecade, twice for the second decade, thrice for the thirddecade, and so on.

contd…



The method thus, assumes that the growth rate in the first decade is

@(x+y), is in the second decade @(x+2y), and in the nth decade

@(x+ny).Thus the growth rate is assumed to be varying. It is

expressed as

Pn = P + n x + n(n+1)/2*y

This method will give end results, some where between the results

given by ‘arithmetic increase method , and ‘geometric increasemethod’, and is, thus, considered to be giving quite satisfactory

results.



The geometric progression method, since gives higher

values of forecasted population, evidently gives higher results

for developed cities which do not expand in future at

compound rates; although it may be suitable for new younger

cities expanding at faster rates.

For older cities arithmetic method may be better, although

incremental method is considered to be the best for any city,

whether old or new.



DECREASING RATE METHOD

•Since the rate of increase in population goes on reducing, as the

cities reach towards saturation goes on reducing, as the cities reach

towards saturation, a method which makes use of the decrease in

the percentage increase, is many a times used and gives quite

rational results.

• 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.

• This method is however, applicable only in cases, where the rate

of growth shows a downward trend.



SIMPLE GRAPHICAL METHOD

In this method, a graph is plotted

from the available data ,

between time and population.

The curve is then smoothly extended up to the desired year.

This method, however, gives very approximate results, as the extension

of the curve is done by the intelligence of the designer.



• All the five method described as far are based on assumption

that factors and conditions which were responsible for

population increase in past will even continue in future also,with same intensity. That is a vague assumptions and may or

may not be satisfied.

• However they are less time consuming. They are also some

other advanced methods available for population forecastingwhich includes:

1). COMPARATIVE GRAPHICAL METHOD

2). MASTER PLAN METHOD

3). RATIO METHOD

4). LOGISTIC CURVE METHOD



COMPARATIVE GRAPHICAL METHOD: based on assumption that city

under consideration may develop same as the selected similar cities developed

cities. It is based on logical background, precise and reliable results can be

obtained.

MASTER PLAN METHOD: the master plan prepared for a city is generally

such as to divide the city into various zones, and separate the residence,

commerce and industry from each other. The population densities is fixed .

RATIO METHOD OR APPORTIONMENT METHOD: In this method of

forecasting future population of a city or a town, the city’s census population

record is expressed as the percentage of population of the whole country.

LOGISTIC CURVE METHOD: based on assumption that the population of a

city shall grow as per logistic curve under normal conditions.



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