Causal pathways underlying global soil moisture-precipitation coupling.

Area of Science:

• Earth System Science
• Atmospheric Science
• Hydrology

Background:

• Surface soil moisture-precipitation (SSM-P) coupling is vital for climate dynamics.
• Sensible heat (SH) and evapotranspiration are key mediators, but their global mechanisms are poorly understood.
• This knowledge gap hinders accurate hydrometeorological predictions.

Purpose of the Study:

• To investigate global SSM-P coupling pathways and their underlying mechanisms.
• To identify hotspots of land-atmosphere interaction.
• To evaluate the performance of climate models in simulating these processes.

Main Methods:

• Utilized an information flow technique applied to satellite observations and reanalysis data.
• Analyzed global land areas to identify SSM impacts on precipitation.
• Investigated the roles of sensible heat and evapotranspiration in coupling pathways.

Main Results:

• Identified significant local SSM impacts on precipitation across approximately 16% of global land.
• Discovered eight coupling hotspots, with SH-mediated pathways dominant globally.
• Noted exceptions in African hotspots where evapotranspiration-mediated pathways prevail, linked to moisture and boundary layer variability.
• Found that strong coupling correlates with high SSM variability, especially for SSM-SH-P.

Conclusions:

• Most CMIP6 models inadequately represent observed SSM-P coupling patterns.
• Only a few models accurately captured the variability-causality relationship derived from ERA5 data.
• Proposed process-based metrics for enhancing climate model evaluation regarding land-atmosphere interactions.