3. Basic demographic processes:
Births = Natality
Deaths = Mortality Note: mortality ≠ morbidity!
Migration
Demographic balancing equation:
Population change = (Births – Deaths) + (Immigrants – Emigrants)
or
∆P = Pt – P0 = (B – D) + (I – E) (1)
where P0 is the initial population and Pt is the population after time t.
Demographic balancing equation (1) can be split into 2 basic components:
Natural increase = Births (B) – Deaths (D)
Net Migration = Immigration (I) – Emigration (E)
Natural increase is the most important component of the overall population change.
Population Growth Rates
Each component of population change (births, deaths, migration) can be expressed as an absolute number (pop change) – crude values or more commonly, as annual rates expressed in %.
Demographic rates are ordinarily calculated per 1000 persons per year.
Birth Rate = Humans born per 1000 individuals per year.
Death Rate = Humans died per 1,000 individuals per year.
Since population is changing throughout the year, we use for calculations mid-year population, which is the population in the middle of the particular year.
Crude Birth Rate (СBR) = total number of live births per year per thousand mid-year population.
Crude Death Rate (СDR) = total number of deaths per year per thousand mid-year population.
CBR =
1000,
where # births is number of births during one year,
is mid-year population. Mid-year population can be calculated as
average number between two population values: at the beginning and at
the end of the year.
CDR
=
1000,
where # deaths is number of deaths during one year,
is mid-year population.
Crude (Natural) Growth Rate (CGR) = natural (population) growth per year per thousand mid-year population:
CGR = CBR – CDR
This is a natural growth rate. The total growth rate is different, since it includes immigration, emigration.
Crude (Natural) Growth Rate, or just Crude Growth Rate may be also calculated this way:
CGR =
1000,
where
- population change during one year.
Note: CGR as well as other crude rates, may be expressed in %.
Example 1: suppose that CGR = 15. How many percent was population growth?
It means that natural increase in population is equal to 15 persons per 1000 population per year. To convert it to %, use the following proportion:
15 people per 1000 population
X people per 100 population
Solving proportion, find X:
=
1.5%
You may have noticed that 1.5% can be obtained from 15 by just dividing by 10!
1.5% represents annual rate of population growth.
The average rate of population growth over some extended time period can be calculated if the population size at two points in time is known.
Exponential growth formulas:
Population growth is described by exponential function:
Pt = P0×(1+r)t (1)
where Po is the initial population, Pt is population at the end of t years, r is annual growth rate expressed as a decimal.
For t = 1 year, that is for annual population growth the formula (1) will look simple:
Pt = P0×(1+r) (2)
Example 2. Annual population growth rate is 6%. Assuming that the initial population of certain country at the beginning of the year was 10 mln, find its population by the end of the year.
P0 = 10 mln r = 0.06 (6%) Pt = ?
Using formula (2), we get:
Pt = 10 mln *(1+0.06) = 10.6 mln people
Applying
fundamental limit rule to formula(1) at high
t values (more
accurately, at
),
we get:
(3)
where Pt - population in t years from 0 time; P0 - population in time 0;
t represents number of yrs and r is annual rate of growth ( decimal).
Formula (3) is convenient for calculations and even at relatively small t gives good approximation.
Population doubling time = the number of years until the population will double if the annual rate of growth remains constant.
Rule of 70
for calculating doubling time: T2
=
,
where r
is annual growth rate in
%.
Urban problems in developing & developed countries
In developing contries:
Dense traffic, smoky factories, use of wood or coal fires cause excessive air pollution.
Lenient pollution laws, corrupt officials and ignorance cause even more pollution.
Only 35% of urban residents in developing countries have satisfactory sanitation services.
In developed countries
The rapid growth of central cities in Europe and North America has now slowed or even reversed.
The good news is better air and water quality, safer working conditions, fewer communicable diseases.
The bad news is urban decay and sprawl and transportation issues have worsened
Urban Sprawl - is a Current Developed World Problem
In most American metropolitan areas, the bulk of new housing is in large, tract developments that leapfrog beyond city edges in search of inexpensive land.
Urban sprawl consumes about 200,000 ha of US agricultural land annually.
Planning authorities are often divided among many small local jurisdictions.
Most American cities devote ~1/3 of their land area to cars.
Freeways have reshaped our lives.
Public transportation is expensive and difficult to establish.
Ways to achieve urban sustainability
Urban Sustainability in Developed World
Limit city size, or turn into modules of 30-50,000 people.
Maintain greenbelts in and around cities.
Determine in advance where development will take place.
Locate everyday services more conveniently.
Encourage walking and low-speed vehicles.
Promote more diverse, flexible housing as an alternative to conventional housing.
Grow food locally, recycling wastes and water, etc.
Invite public participation in decision-making.
Cluster housing, or open-space zoning, which preserves 1/2 of a subdivision as natural areas (open space).
Sustainable Development in the Third World
Social justice and sustainable economic development are answers to urban problems.
Institution of social welfare providing care to the sick and elderly.
The best way may be for developing countries to delink from international economic systems and develop self-sustainability.