Reassessing sea-level rise attribution: global soil moisture shows no widespread drying trend

This study uses multiple data sources, including remote sensing products (ESA CCI and SMAP), reanalysis data (ERA5), and ground-based observations from the International Soil Moisture Network (ISMN), to systematically analyses the change in global surface soil moisture from 1983 to 2023. Contrary to recent findings suggesting a decline in soil moisture has contributed to sea-level rise via groundwater release in the 21st century, our multi-source analysis does not indicate a significant, widespread drying trend on a global scale. Results reveal substantial discrepancies among datasets: from 2000 to 2023, the CCI product indicates moistening over approximately 89.22% of global land area, particularly in eastern North America, eastern South America, southern Africa, and eastern Asia, whereas ERA5 shows drying over 68.39% of land area. The SMAP product exhibits an intermediate trend during 2015–2023. Analysis based on global station data further confirms a strong positive correlation between surface and subsurface soil moisture (especially within 0–40 cm), supporting the use of remotely sensed surface information to infer deeper soil water conditions. We argue that the drying signal in ERA5 likely arises from model artifacts, including overestimated canopy interception evaporation in its land surface model and systematic underestimation of precipitation in its forcing data. Thus, the global drying trend reported in some model-based studies may not reflect actual terrestrial water storage changes. This study underscores the importance of using multi-source observations to critically evaluate hydrological change and cautions against drawing large-scale conclusions about soil moisture decline and its implications for sea-level rise based on single-model outputs. In addition, we highlight the need to improve retrieval algorithms, and refine model physics to enhance the monitoring and understanding of soil moisture changes in climate and hydrological studies.