Hydrodynamic modeling and risk assessment of surge events in the Kazakh sector of the Caspian Sea

The Caspian Sea, a crucial economic resource for its littoral states, is increasingly affected by sea level decline and surge phenomena. Oil and gas extraction, fisheries and maritime transport are among the primary economic activities in the region. However, decreasing water levels and recurrent surges, particularly in the northeastern part of the sea, pose growing risks to these operations. This study investigates the spatial and temporal characteristics of 1836 surge events recorded in the Kazakh sector from 1940 to 2022, comprising 1086 up surges and 750 down surges. Up surges predominantly occurred in spring and autumn, while down surges peaked in September. To evaluate the potential impact of these surges, a hydrodynamic model (MIKE 21) was applied, utilizing ERA5 reanalysis data for surface wind and atmospheric pressure. Model validation against in situ measurements showed excellent performance (R2 = 0.98, RMSE = 0.11 m). Simulations of 14 extreme events revealed that up surges can cause inland flooding up to 33.5 km, while down surges can induce coastal retreats up to 32.2 km. These results demonstrate the need for robust early warning systems and integrated coastal risk management to mitigate the socio-economic impacts of surge events in the Caspian region.