Trend shifts and hydroclimatic drivers of Caspian Sea Level (2003–2024) revealed by GRACE and multi-source observations

Caspian Sea This study estimated Caspian Sea level (CSL) variations during 2003–2024 using multi-source datasets, including observations from the Gravity Recovery and Climate Experiment (GRACE), accounting for leakage correction and steric effect, which significantly improved consistency with satellite altimetry. Through wavelet decomposition, we reconstructed distinct periodic components and the underlying trend signal. Change-point detection of the trend revealed four linear phases of CSL variations during 2003–2024: rapid rise (6.66 cm/yr, 2003/01–2006/02), sustained decline (-9.99 cm/yr, 2006/02–2016/08), slowed decline (-3.32 cm/yr, 2016/08–2019/06), and accelerated drop (-23.18 cm/yr, 2019/06–2024/12). Subsequently, difference integral curves and wavelet coherence analysis were applied to investigate the primary driving mechanisms of hydroclimatic factors—precipitation, evaporation, and runoff—on CSL variations. Results showed that at annual scale, runoff and CSL were nearly in phase; while at interannual scale, different factors dominated in different periods. From 2003–2016, runoff trends closely matched CSL variations. Between 2016 and 2019, despite decreased precipitation and intensified evaporation, runoff increased, resulting in a brief period of slow CSL decline. During 2019–2024, a sharp drop in precipitation, intensified evaporation, and reduced runoff jointly contributed to the accelerated CSL decline. If current hydroclimatic conditions persist, the CSL will continue to decline rapidly, posing serious challenges to regional ecosystems and resource management. • GRACE-based Caspian Sea level improved using leakage correction and steric effects, with better agreement with altimetry. • Wavelet and change-point analyses identified four CSL phases from 2003 to 2024, including rapid decline after 2019. • Integral curves and wavelet coherence showed how precipitation, evapotranspiration, and runoff drive CSL changes.