Hydrological response to anthropogenic activities and climate change in the southern Caspian Sea, Iran

Rivers play a vital role in supplying fresh water for various sectors. During the last decades, increasing anthropogenic activities and climate change have altered river flow regimes around the globe. Rivers flow in the southern Caspian Sea in Iran has altered due to water-intensive socio-economic development and climate change. To assess and quantify the impact of anthropogenic activities and climate change on river flow regimes, the elasticity-based methods and the Budyko hypothesis were applied to 40 rivers on the closest gauges to the Caspian Sea were selected. Furthermore, to evaluate spatial/temporal change in hydrometeorological variables, two non-parametric methods, including the modified Mann-Kendall method (MK3) and Innovative Trend Analysis (ITA), were applied. The results showed an alarming trend of increasing temperature and potential evapotranspiration and decreasing rivers’ flow in the southern Caspian sea. Assessing and quantifying the impact of anthropogenic activities and climate change on river flow alteration indicated that anthropogenic activities (accounting for 83.3%) played a dominant role in river flow alteration that led to inflow to the Caspian Sea decline by about 2,412 MCM annually. In addition, the inflow to the Sea has decreased by about 551 MCM every year due to the impact of climate change. Decreasing the inflow to the Caspian Sea can accelerate the declining trend of the Sea level, which leads to boosts eutrophication conditions in the Sea, and negatively affect the ecosystem and economics of the Caspian Sea. Therefore, an appropriate adoption approach must be taken into account to alleviate the environmental and socio-economic issues in the southern Caspian Sea.