Desertification vulnerability in Varamin Plain, Central of Iran
Each indicator was weighted in relation to its influences on desertification process.
Each of indicators is assigned a score ranging from 100 (best) to 200 (worst). Value zero is assigned to the areas where the measure is not appropriate and /or those which are not classified (e.g. water bodies, urban areas, etc.). The function representing the variation of the indicators (scores) is liner ranging between the extreme values (100 - 200). The tables 1 to 3 show the classification of each layer.
The integration was done using GIS technology and with help of ArcView 3.1 Software, the various information layers for each index were collected, prepared in a suitable format then overlaid in order to calculate the index as the geometric mean of the parameters related to each singe index according to the following equation:
Index _ X = [( Layer _ 1) . (Layer _ 2). … . (Layer _ n)] ¹/n
Where n is the number of indicators for each index. And the geometric mean of the three Index gives the ESA index:
ESA = (GWI * LUI * SI) ¹ / ³
Values of three indexes are subdivided into three classes of equal range:
1- high : 100-133
2- medium : 134-166
3- low : 167-200
And ESA index was classified by four main classes of land degradation as high (ESA from 175 to 200), medium (ESA from 150-174), low (ESA from 125-149) and absent (ESA from 100 to 124).
Table 1. Groundwater layers, classification and relative scores
| Layer |
Classes |
Scores |
| Color (CL) |
< 250 |
100 |
| (mg/lit ) |
250-500 |
125 |
| |
500-1500 |
150 |
| |
1500-3000 |
175 |
| |
> 3000 |
200 |
| Electrical conductivity (EC) |
< 250 |
100 |
| (µmho/cm) |
250-750 |
125 |
| |
750-2250 |
150 |
| |
2250-5000 |
175 |
| |
>5000 |
200 |
| Water table |
> 315 |
100 |
| (cm) |
285-315 |
150 |
| |
< 285 |
200 |
| SAR |
< 10 |
100 |
| |
10-18 |
133 |
| |
18-26 |
166 |
| |
> 26 |
200 |
Table 2. Land use and relative Scores
| Land use classes |
Score |
| Agricultural lands |
100 |
| Range lands |
133 |
| Range lands (poor and degrade) |
166 |
| Barrennless |
200 |
Table 3. Soil layers and relative Scores
| Layer |
Classes |
Scores |
| Soil EC |
< 4 |
100 |
| (mmho/cm) |
4-8 |
120 |
| |
8-16 |
140 |
| |
16-32 |
160 |
| |
32-64 |
180 |
| |
> 64 |
200 |
| Soil SAR |
< 8 |
100 |
| |
8-13 |
125 |
| |
13-30 |
150 |
| |
30-70 |
175 |
| |
>70 |
200 |
| Soil Texture |
Course |
100 |
| |
Medium |
125 |
| |
Medium - fine |
150 |
| |
Fine |
175 |
| |
Very fine |
200 |
| Soil Organic Matter |
> 3 |
100 |
| |
2-3 |
125 |
| |
1-2 |
150 |
| |
0.5-1 |
175 |
| |
< 0.5 |
200 |