Sensitivity of soil moisture to precipitation and temperature over China: Present state and future projection

Soil moisture (SM) is a key variable in the climate system as it regulates the latent and sensible heat partition and influences eco-hydrological processes. A few studies have highlighted the increasing frequency of SM droughts at the river basin scale in China, however, little is known about the SM response to precipitation (P) and near-surface temperature (T) at national and regional scales. In this study, the long-term SM dynamics based on a sophisticated land surface hydrological model (i.e., the Variable Infiltration Capacity, VIC) were identified after model evaluation. A simple but effective sensitivity-based approach was developed to quantify the elasticity (ε) and sensitivity (S) of SM to P and T, and the SM was projected for the near future at the regional scale. The results indicate that China has experienced slightly wetter soil conditions during the past five decades and the SM has increased in the arid and semi-arid regions of China, i.e., the North East (0.11 mm/yr) and the North West (0.047 mm/yr). The elasticity and the sensitivity of SM are the highest in the humid region (i.e., South East China), indicating that small increases of P and T are likely to induce considerable changes in the SM relative to other regions. The sensitivity-based approach could perform SM estimation similar to the complex VIC modeling. This approach projected that North China (-5.05 ± 2.31%) and South West China (-5.95 ± 2.04%) are likely to experience drying with a considerable decline in SM due to reduction in P and rise in T in the near future period from 2020 to 2050. The slightly wet soil conditions in the past and a drying future scenario may imply a contrasting consequence for the regional-scale hydrological cycles.