Soil moisture continues declining in North China over the regional warming slowdown of the past 20 years

Abstract

AbstractSoil moisture is an important variable of the climate system and is used to measure dry–wet change in hydro-climate. The warming trend has slowed in China over the past 20 years since 1998, and how the soil moisture changes in this period deserves our attention. With North China as a research region, this study uses the Global Land Data Assimilation System and ground observations to investigate the causes of changes in soil moisture during 1998–2017 versus 1961–1997. The results show that: (1) annual mean soil moisture experienced an almost continued decrease from to 1960s to 2010s, and no pause in the decrease of soil moisture over the regional warming slowdown of the past 20 years could be detected; (2) with the stabilization or even increase in solar radiation and wind speed as well as the continuous increase land surface air temperature, the impact of potential evapotranspiration on soil moisture gradually became prominent, and the impact of precipitation decreased, since 1998; (3) the percent contribution of annual potential evapotranspiration to soil moisture variation increased by 26% during 1998–2017 relative to that in 1961–1997, and the percent contribution of summer potential evapotranspiration even increased by 45%. Our results will provide insight into the land surface water budget and mechanism involved in drought development in North China.