Ammar Rafiei Emam, Farhad Fakhri
Faculty of natural resources, university of Tehran, Karaj P.O.Box 31585-4314, Tehran, Iran.
E-mail: [email protected]
Ali naghi Rafiei Emam, Amir Ahmadian
Faculty of economic, university of Tehran,Tehran, Iran.
Tel : +98 911 2499262, Fax: +98 21 8966760
Email: [email protected]
Desertification is a world-wide phenomenon which causes the earth’s ecosystems to deteriorate. It affects about two-thirds of the countries of the world, and one-third of the earth’s surface, on which one billion people live, namely, one-fifth of the world Population. Desertification, as defined is the degradation of the land in arid, semi-arid and sub-humid dry areas caused by climatic changes and human activities. A reduction in the natural potential of the land and depletion in surface and ground water resources accompany it.
The vulnerability of land to desertification is mainly due to Overgrazing and woodcutting, over cultivation practices, and improper water management leading to salinization is the cause of the deterioration of irrigated lands. In addition to vegetation deterioration, erosion, and salinization, desertification effects can be seen in loss of soil fertility, soil compaction, and soil crusting. Urbanization, mining, and recreation are having adverse effects on the land of the same kind as is seen on range, dry farming, and irrigated lands.
As a matter of fact, Desertification is a land degradation problem of major importance in the arid regions of the world. Deterioration in soil and plant cover has adversely affected nearly 50 percent of the land areas as the results of human mismanagement of cultivated and range lands.
Material and Methods
Land degradation involves as complex set of processes of factors, which interact in space and time leading to a decrease in land productivity. Thus, it is necessary to identify the various indicators, which will provide the relevant information to define the desertification prone areas. To this aim, the MEDALUS (Mediterranean Desertification And Land Use: European Commission, 1999) methodology was modified and adopted, and the risk of desertification was evaluated on a regional level by defined the ESA (Environmental Sensitive Area) Index. ESAs method takes into consideration three broad systems of indicators:
- Ground Water Indicators (Water Table, Cl, Ec, Sar)
- Land use indicator
- Soil quality indicators (Ec , Sar, Organic Mater ,Texture )
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)] ?/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) ? / •
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
|Color (CL)||< 250||100|
|Electrical conductivity (EC)||< 250||100|
|Water table||> 315||100|
Table 2. Land use and relative Scores
|Land use classes||Score|
|Range lands (poor and degrade)||166|
Table 3. Soil layers and relative Scores
|Soil EC||< 4||100|
|Soil SAR||< 8||100|
|Medium – fine||150|
|Soil Organic Matter||> 3||100|
Results and Discussion
The results have been showed in 1 to 3 figures, and fig 4 shows the ESA map.
Figure 1. Map of GroundWater Index
Figure 2. Map of Land Use Index
Figure 3.Map of Soil Quality Index
Figure 4. Map of ESA Index
The map of ESA index shows that in the central part of plain and along the northeastern it, there isn’t any risk of desertification. But in the south western and in the limited area in southeastern the risk of desertification is high. And the others part of plain the risk of desertification is low to high. The results shows that from the total area of plain about 58 134 ha is in the Absent class, 33 578 ha is in the low class, 31 665 ha is in the medium class and about 7 812 ha is in the high class and about 2859 ha is not classified, because these places are city, Village or water body.
With attention to the above results, although in 1 class the risk of desertification is low but the management in these lands are very necessary and important because these lands are generally of rangeland and also agricultural (the fallow is the most) and may be in affect of mismanagement, change to medium class. And in the south of plain that are medium to high classes, generally have drainage problems and also salinization; therefore we should be restrain of desertification speed with the soil improvement and others planning in these lands.
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