Climate warming accelerates surface soil moisture drying in the Yellow River Basin, China

Understanding the dynamic response of surface soil moisture (SSM; 0-7 cm) drying to rising temperature is vital to predict future changes in agricultural and hydrological drought. Here we use quantile regression to explore the scaling effects of 2-m air temperature on SSM (%/degrees C) of the driest month in 8 different land cover types in the Yellow River Basin by using temperature intervals and a sliding window approach. SSM decreases significantly with air temperature and decreases more rapidly in warmer conditions, except for plain field, suggesting that temperature has a greater effect on SSM-temperature scaling than land cover. For warmer conditions, scaling exhibits larger spatial heterogeneity, indicating that it is mainly affected by local factors. When SSM is moderate, the scaling is constrained by various factors, but mainly by temperature. Comparatively, the scaling is close to 0 when SSM is very high or very low. The study highlights that global warming effects on drought may be underestimated. The findings provide an important theoretical basis for effects of temperature on soil moisture and future drought prediction.