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Assessing land surface drying and wetting trends with a normalized soil water index on the Loess Plateau in 2001–2016

Wang, Yinyin, Magliulo, Vincenzo, Yan, Weiming, Shangguan, Zhouping
The Science of the total environment 2019 v.676 pp. 120-130
drought, drying, ecosystems, evapotranspiration, rain, soil depth, soil water, surface storage, China
Long-term drought may cause severe damage to ecosystems. To assess drought intensity, we introduced a normalized soil water index (NSWI) of land surface, on the basis of rainfall and actual evapotranspiration. Areas undergoing land surface drying on the Loess Plateau in 2001–2016 were assessed on the basis of the values of NSWI combined with rainfall and land surface water storage (LSWS). The extent of soil drying and wetting at depths of 0–0.01 m, 0–0.1 m and 0–2 m was also quantified. Results showed that up to 7.16% of the Loess Plateau was subjected to decreasing LSWS. On an inter-annual time scale, land surface drying intensified starting in 2003, and this pattern was chiefly evident at the soil depth of 2 m. The approach proposed in this study could also be used to identify temporary dry soil layers (DSLs) in arid ecosystems.