Response of the Caspian Sea Shoreline to hydro-climatic Drivers Variation

During the past three decades, seawater level (SWL) in the Caspian Sea has declined by about 2 m, and sea area has decreased by about 15 000 km². This has affected coastal communities, the environment and economically important sea gulfs (e.g., Dead Kultuk). We simulated SWL using total inflow from feeder rivers and precipitation and evaporation over the sea to assess the effects of coastline change and evaluate zones vulnerable to desiccation. We determined the potential of coastal vulnerability over the past 80 years by comparing the minimum and maximum annual water body maps (for 1977 and 1995). We then determined the linear regression between SWL rise and covered potential vulnerable area (CVA), using annual Normalised Difference Water Index (NDWI) maps and SWL data from 1977 to 2018. Combining SWL-CVA regression and SWL simulation model enabled us to determine desiccated areas in different regions of the Caspian Sea due to changes in precipitation, evaporation and total inflow. The results showed that 25 000 km² of the sea is potentially vulnerable to SWL fluctuations to be desiccated. Also, we found 70% of this vulnerable area is in Kazakhstan. Potential vulnerable area per kilometer coastline was found to be 6 km² in Kazakhstan, 4 km² in Russia and the whole of the Caspian Sea, 1.5 km² in Iran, 1 km² in Azerbaijan, and 0.5 km² in Turkmenistan. The results also indicated that SWL in the Caspian Sea is sensitive to evaporation and that, e.g., a 37.5 mm decrease in mean annual net precipitation would lead to an 1875 km² decrease in the sea area, while a 1 km³ decrease in mean annual inflow would lead to a 1400 km² decrease in the sea area. Thus the developed framework enabled the spatial consequences of changes in water balance parameters on sea area to be quantified. It can assess future changes in SWL and sea area due to anthropogenic activities and climate change.