Evaluation and Zoning of Desertification Iintensity Potential Under the Influence of Groundwater Resources and land Subsidence in Sefid-Rud Basin

Introduction: Desertification is the reduction of the ecological and biological power of the earth, which occurs in two natural and artificial ways. This phenomenon is one of the important problems of the countries in the framework of the sustainable development management plan, which is the result of a set of different environmental, human and climatic factors. The purpose of this study is to investigate the impact of the level drop and the change in the quality of underground water and land subsidence in the occurrence of desertification and land degradation in Sefidroud watershed using the IMDPA model.
Material and Methods: In this research, it has been tried to use quantitative and qualitative indicators of underground water such as electrical conductivity (EC), water level drop, sodium absorption ratio (SAR) as well as land subsidence map and their classification according to desertification intensity. Then, the final map of desertification intensity was obtained by combining maps of the intensity of qualitative degradation and the drop of the underground water level, as well as the land subsidence map as a soil criterion using the geometric mean. Finally, the zoning map of desertification intensity was prepared using the final risk classes of desertification according to the geometric mean of the values of the risk classes of quantitative and qualitative indicators.
Results and Discussion: The obtained results showed that the electrical conductivity (EC) map showed that 64.8% of the catchment area is in the medium class, 0.5% in the extreme and very extreme class. Also, the sodium absorption ratio (SAR) zoning map showed that 100% of the catchment area has a value of less than 18 and is in the low or insignificant category. The zoning of the water level drop also showed that only 6% of the studied catchment area is in the moderate class, 29% is in the extreme and very extreme class. The map of different levels of land subsidence showed that only 2% of the area of the watershed was involved in subsidence. The maps of the classes of desertification intensity of the Sefidroud basin, respectively, with subsidence and without subsidence respectively, show that 47% and 0.4% of the studied area have high desertification intensity, also in the state of intense desertification. Desertification with subsidence (51.5 percent) and without subsidence (90 percent) is the predominance with the intensity of desertification class.
Conclusion: The results showed that the electrical conductivity factor of underground water can have a significant effect on the intensity of desertification, on the other hand, the studies conducted on the weighted average of the indicators show that sodium absorption ratio index has the least effect in the region. The results of the integration of the three parameters of the underground water model (IMDPA) in Sefidroud basin showed that about 90% of the basin has an average state of desertification, which can be caused by the influence of the average state of the electrical conductivity index in a significant part of the basin. However, the effect of the drop in the underground water level in the areas that had severe desertification from the point of view of the electrical conductivity index caused these areas to have a very severe desertification condition according to the groundwater standard, which is well within the study areas of Gol -Tepe-Zarin-Abad can be recognized.