Understanding global soil moisture-air temperature (θ-Ta) coupling is needed to improve the representation of land-atmosphere interactions in Earth system models. Most studies on θ-Ta coupling have focused on hot extremes, where precipitation-related indices and model-derived soil moisture products are commonly used. In this study, global θ-Ta coupling is examined based on monthly air temperature anomalies and the Gravity Recovery and Climate Experiment (GRACE) terrestrial water storage (TWS). A discrete wavelet decomposition is used to partition the TWS into different components. The results show that TWS is useful in revealing the spatial patterns of θ-Ta coupling. Decomposed GRACE TWS shows improved skill compared to raw TWS in explaining temporal variability of monthly air temperature, which likely reflects different roles of soil moisture at different depths in the θ-Ta coupling. The explanatory power improves further by using a combination of decomposed GRACE TWS and precipitation. Such improvement is observed particularly in places where vegetation tends to have a deeper rooting system, such as eastern region of South America, the southern tip of Africa, and north of the Tropic of Capricorn in Australia. The occurrence of θ-Ta coupling is mainly constrained by the coupling of root zone moisture and land surface temperature. In addition to deeper rooting systems, clear wet and dry season alternation is another favorable factor for developing significant monthly θ-Ta coupling.
- air temperature
- soil moisture