Dry biases in land water storage and excessive soil moisture limitation in CMIP6 models

Accurate representation of plant water availability is crucial for climate modeling, due to its significant role in land-atmosphere interactions. Our study focuses on water storage dynamics and analyzes how soil moisture limitation is represented in Earth System Model (ESM) simulations of the Coupled Model Intercomparison Project phase 6 (CMIP6). We first quantify the long-term maximum annual depletion in water storage, contrasting model results with estimates based on satellite observations of terrestrial water storage from the Gravity Recovery and Climate Experiment (GRACE), as well as remotely sensed estimates of the water balance. Our analysis shows that CMIP6 models mostly underestimate the maximum annual soil moisture depletion, especially in the Amazon region. We further assess the frequency of soil moisture limitation in CMIP6 simulations against observations from solar-induced fluorescence (SIF) and GRACE, finding that ESMs generally overestimate this frequency. We obtain consistent results when comparing models to ground observations at 128 sites from the FLUXNET2015 dataset. Our study highlights the importance of improving the representation of plant water availability and land-atmosphere interactions in Earth System Models. Implementation of new model features could have large implications in predicting future climate on land.