Geography Reference
In-Depth Information
models. The soil attribute dataset were from 1:10,000,00 soil database built up in
the second general survey of soil in China, and interpolated with the Kriging
interpolation algorithm. This dataset includes data of loam proportion, organic
content, Nitrogen content, phosphorus content, potassium content, the content of
rapid available phosphorus, the content of rapid available potassium, pH value.
3.2.1.3 Models
The Agriculture and Land Use (AgLU) module of GCAM and simulated land use
change trend data under three scenarios in the future were used to complete the
structure land use simulation. AgLU module is a dynamic partial equilibrium
economic model, at the core of the AgLU model is a mechanism that allocates land
among cropland, grassland, forestry area, and other land and the economic return
from each land use type in each region is maximized. The three primary drivers of
land use change are population growth, income growth, and autonomous increases
in future crop yields.
As there is no simulation function for built-up area in the GCAM model, an
econometric model is set up to simulate the built-up area. In order to optimize the
simulation results, the coefficients in the econometric model were calibrated
according to the variation of population, GDP and urbanization ratio year by year.
The major driving factors in GCAM model are GDP and population with no
urbanization ratio involved in, thus, urbanization ratio variable should be added.
American urban geographer Northam has researched the process of urbanization in
various countries in the world (Northam
1971
). His studies indicated that the
process of urbanization was expressed as an S. Therefore, the equation is built as
follows:
y ¼ 1
=ð
1
þ
o
e
bt
Þ
ð
3
:
9
Þ
where y represented the urbanization ratio, t represented time, q and b are
parameters. It could be deformed as follows:
ln
ð
1
=
y
1
Þ
¼ln o
bt
ð
or y
1
¼ a
0
þ
a
1
t
Þ
ð
3
:
10
Þ
The urbanization ratio over the years is obtained from statistical yearbook, and
according to which the parameters q and b in the formula are obtained from the
simulation. Hence, the calculated equation of urbanization is worked out as
follows:
y
¼
1
=ð
1
þ
4
:
5748e
0
:
04t
Þ
ð
3
:
11
Þ
