Erosión y desertificación.-Risk evaluation of ground water table decline as a type of desertification. A case study area: Southern Iran

Abstract

ABSTRACT This paper presents a model to assess risk of ground water table decline. Taking into consideration eleven indicators of lowering of ground water table the model identifies areas with ‘Potential Risk’ (risky zones) and areas of ‘Actual Risk’ as well as projects the probability of the worse degradation in future. The Mond river basin, located centrally to this zone, has been selected as a test area to assess the risk of lowering of ground water table. For this purpose two sub basins of the Payab and Qareh Aghaj have been chosen for detailed study. By fixing the thresholds of severity classes of the eleven indicators a hazard map for each indicator was first prepared in GIS. The risk map was prepared by overlaying eleven hazard maps in the GIS, deploying the new model. The GIS analysis has made it possible to distinguish the areas with ‘potential risk’ from those widespread areas that showed the ‘actual risk’ of lowering of water table. Although the areas under potential risk form a lower proportion in the both sub basins, but the vulnerable potential risk areas with moderate and severe classes are more in the Qareh Aghaj plains compared to the Payab. A conclusion is that the already over evacuated lands (severe risk + moderate actual risk) are more widespread in the Qareh Aghaj plains (54%), with semi arid climate, compared to the Payab (10%), with arid climate. Areas under potential risk when classified into subclasses with different probability levels the model projects a statistical picture of the risk of lowering of ground water table.