Assessing the role of meteorological and hydrological droughts on the drying up of the Bakhtegan and Tashk lakes

The Bakhtegan and Tashk lakes, as the second largest lakes in Iran, have been faced with a drought since 2007. Consequently, the ecology of the region has been disrupted and the social, health and environmental problems have been appeared. The purpose of this study is to investigate the role of meteorological and hydrological droughts on the drying up of these lakes. For this purpose, temperature and precipitation data measured at 21 rain gauge stations, flow rate measured at three hydrometric stations and the area obtained from the calculation of the normalized water differential index by processing 46 Landsat satellite images. Pearson correlation coefficient was used to determine the relationship between variables and linear regression method was applied to examine the trend each variable time series. Also, to determine the effect of climatic drought and hydrology on changes in the area of lakes, standardized 12-month rainfall and runoff indices were used. A decreasing trend has been discovered in the lakes area since 2008, and most of the lakes have been dried after 2012. Despite an increasing trend in the basin temperature (0.04°C/year), no significant change in this trend was observed in 2008. Moreover, decreasing trends have been detected in precipitation and discharge of the Kor River (the most important inlet of lakes), especially since 2007. The calculated standard precipitation and runoff indices indicated occurring of meteorological and hydrological droughts in the basin since 2008. Precipitation during the drought period decreased by 47%, but the discharge of the river into the lakes decreased by more than 95%. According to the results of this study, although rising in temperature together with the meteorological and hydrological droughts have caused reducing of the lakes area, but other factors could play an important role in this hazard. To determine the role of other effective factors, considering the role of human factors (especially agricultural development and dam construction) is also suggested.