Climate change and anthropogenic effects on the drying of a saline lake in an arid region (Namak Lake, Iran)

The drying up of the saline Namak Lake (NL) is one of the most severe environmental problems facing Iran's central plateau. A sharp decline (reduction of 509 km(2)) was identified in the NL area based on the NDWI (Normalized Difference Water Index) index over the last three decades. Therefore, the fluctuations and probable impacts on the NL area were investigated using a comprehensive approach from three perspectives: climatic, hydrologic, and anthropogenic. Ten-hydrologic, eight-climatic, and four-human-made indices were obtained using local and satellite datasets (Landsat, ERA5-Land, and GRACE datasets on the Google Earth Engine (GEE) platform). The long-term spatio-temporal variations of parameters were explored by applying the Mann-Kendall test over the last three decades. The results indicated a significant warming trend with a non-significant rainfall trend and a sharp decline in the basin's surface and groundwater levels, particularly following the construction of the 15-Khordad Dam. Dam construction had significant effects on the basin's hydrological regime, especially by reducing annual, monthly (up to 90%), and 1-day maximum streamflow values. Investigation of long-term vegetation coverage changes with the NDVI (Normalized Difference Vegetation Index) and EVI (Enhanced Vegetation Index) indices showed a growing trend, especially since 2012, as a result of an increase in farmland area under cultivation. Then, the contribution of each of these parameters to the NL area's fluctuations was investigated using machine learning and Deep Neural Network (DNN) methods, revealing the prevailing nonlinear relationships and interactions. Using the deep learning method, streamflow values were identified as the most influential factor in reducing the lake's area. These findings suggest that the warming trend and prolonged droughts have hastened the lake area decline. However, human interventions, such as the construction of streamflow control structures, the lack of supply of lake water rights, the overexploitation of groundwater, and agriculture, have been the primary contributors to the lake's demise.