Investigation of Hydrometric Variables in Helmand Basin and its Impact on Land degradation in Sistan Plain

The drying of Hamoon international wetlands and dust storms caused by these wetlands bed in the past two decades have been considered as one of the main environmental concerns of the eastern part of Iran. The purpose of this study was to investigate the relationship between meteorological variables of temperature, rainfall and discharge of the entrance water of the Hirmand River with the amount of land degradation in the Hamoon in a 21-year (1996- 2016) interval. For this purpose, weather data of temperature and precipitation were obtained at three synoptic stations of Kandahar, Farah and Zabol, and TRMM rainfall data and ERA temperature data were obtained from the related website. Land degradation based on the MEDALUS model and five criteria of wind erosion, soil quality, climate quality, management quality and vegetation was evaluated in Hamoon basin. The correlation between temperature, precipitation and discharge data was determined to land degradation statue. Investigations showed that the inflow of Hirmand River inlet to the Hamoon bed has been decreasing during this period, and the land degradation class has increased very drastically in all working units from the middle class to the severe class. Also the correlation of temperature data with inlet water discharge and land degradation were -0.558 (moderate level) and 0.735 (strong level) respectively, while the correlation of discharge with precipitation was 0.666. Correlations between precipitation and discharge with land degradation were found to be strong at 0.901 and 0.843, respectively. The results showed that the land degradation in the bed of the Hamoon has a good correlation with temperature changes, precipitation and inflow discharge. This correlation is such that it shows the indirect relationship between the amount of land degradation with the amount of inflow discharges and recorded precipitation and the temperature is correlated with each other. Between 1996 and 2002, the rate of land degradation increased and reached a very severe level with increasing temperature, decreasing precipitation and consequently reducing the inflow rate of the Hirmand River to the Hamoon. In 2003, with temperature decrease and the increase in precipitation, the inflow rate of the Hirmand River increased and finally the intensity of land degradation was reduced in the medium to high intensity units. In 2004 to 2016, the amount of rainfall in the Hirmand basin declined, with the result that the amount of discharge to the Hamoon wetlands declines again and the intensity of land degradation in the work units is at a very high level.