Evaluation of Soil Moisture in CMIP6 Simulations

Abstract

Abstract This study employs multiple reanalysis datasets to evaluate the global shallow and deep soil moisture in Coupled Model Intercomparison Project phase 6 (CMIP6) simulations. The multimodel ensemble mean produces generally reasonable simulations for overall climatology, wet and dry centers, and annual peaks in the melt season at mid- to high latitudes and the rainy season at low latitudes. The simulation capability for shallow soil moisture depends on the relationship between soil moisture and the difference between precipitation and evaporation (P − E). Although most models produce effective simulations in regions where soil moisture is significantly related to the P − E (e.g., Europe, low-latitude Asia, and the Southern Hemisphere), considerable discrepancies between simulated conditions and reanalysis data occur at high elevations and latitudes (e.g., Siberia and the Tibetan Plateau), where cold-season processes play a driving role in soil moisture variability. These discrepancies reflect the lack of information concerning the thaw of snow and frozen ground in the reanalyzed data and the inability of models to simulate these processes. The models also perform poorly in areas of extreme aridity. On a global scale, the majority of models provide consistent and capable simulations owing to the minimal variability in deep soil moisture and limited observational information in reanalysis data. Models with higher spatial resolution do not exhibit closer agreement with the reanalysis data, indicating that spatial resolution is not the first limiting factor for CMIP6 soil moisture simulations.