| 摘 要： |
Significant soil drying has been reported in the semi-arid Three-North Region of China since the 1980s, yet its dominant drivers and the potential effects on dryland ecosystems are still poorly documented. In this work, the improved Vegetation Interface Processes (VIP) model was employed to characterize the spatio-temporal pattern of the root-zone soil moisture (RZSM) from 1982 to 2015 over the West Liao River Basin (WLRB). Results showed that RZSM decreased in most parts of the WLRB along with precipitation decline and vegetation greening. Sensitivities of RZSM to climate and vegetation dynamics exhibited obvious spatial and seasonal heterogeneity. Averaged over the whole basin, sensitivity of RZSM to precipitation (S-P) is the highest. Significant seasonal differences were found in the sensitivity of RZSM to leaf area index (LAI) (S-LAI). S-LAI values in spring and autumn were generally negative throughout the WLRB, but prominent positive S-LAI values were observed in the north-west forest in summer, owing to the increased drier-and-browner associations in summer induced by the earlier spring greenness. Attribution analysis showed that relative contributions of precipitation, air temperature and LAI changes to the growing-season RZSM (RZSM(GS)) drying trend were 69.0%, 17.5% and 13.5 %, respectively. It can be inferred that precipitation decrease dominated the soil drying over the WLRB, while air warming and vegetation greening accelerated this drying. In a future warming scenario without substantial increase in water use efficiency (WUE), dryland ecosystems might suffer more severe biomass losses caused by complex soil-vegetation-atmosphere interactions. This study can improve our understanding of the terrestrial-atmospheric feedbacks and their possible effects on dryland ecosystems. |
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