Long-term changes in surface soil moisture based on CCI SM in Yunnan Province, Southwestern China

Abstract

Soil moisture (SM) plays an important role in regional runoff variations, energy dynamics, and vegetation productivity. It is also widely used to detecting agricultural drought. Recently, a severe drought occurred in Yunnan Province in southwestern China, so long-term changes in surface SM were of concern. However, there were only 18 SM stations in Yunnan Province, and the longest observation was less than five years; thus, long-term changes in Climate Change Initiative (CCI) SM were investigated. CCI SM and in situ SM had similar trends of temporal variations and a systematic difference. The revised CCI SM was built by a linear regression model based on the relationship between in situ SM at each station and the corresponding grid of CCI SM. The revised CCI SM showed an abnormally low value during the severe drought in 2009, indicating that the monthly revised CCI SM could detect drought in Yunnan Province. SM drought easily occurred during the dry seasons, and the frequency of drought seems to decrease, but the severity of drought increased in the 21st century. The seasonal SM struggled to reflect drought correctly and accurately. CCI SM needs validation before use due to its variable quality. In summary, CCI SM provides a better tool than in situ SM to investigate long-term changes in SM and detect drought, and can be used for climate modeling.