Assessment of ecological drought sensitivity based on water use efficiency.

[Objective] This study accurately quantified the degree of drought sensitivity of ecosystems to provide reference for early warning of ecological drought and reduction of ecological losses. [Method] The standardized ecological water deficit index (SEWDI) was constructed based on the ecological water deficit in Northwest China, and the ecological drought sensitivity was defined by combining water use efficiency (WUE) of vegetation. The Copula method was used to analyze the sensitivity of ecological drought by exploring the probability of WUE increase under the condition of increasing ecological drought. [Result] The ecological water deficit of vegetation in the Tarim Basin, Kunlun Mountains, Turpan Basin, Qaidam Basin and Hexi Corridor was high, with the highest monthly mean value of 75 mm. SEWDI was strongly correlated with WUE in most regions and areas with significantly positive correlation accounted for 24. 2% of the total region, mainly in Xinjiang, western Qinghai and southern Shaanxi. The areas with significantly negative correlation accounted for 36. 8% of the total region, mainly in the Loess Plateau. With the intensification of ecological drought, the sensitivity of WUE to ecological drought was not tnonotonically increased in different regions. The sensitivity of WUE to ecological drought increased with the increase of drought stress during the vegetation growth period, and the sensitivity of ecological drought in grassland was higher than that in forest land and cropland. The rate of increase in WUE probability from May to June was the fastest, and the monthly average rates of increase in WUE probability in the conditions of light drought-moderate drought, moderate drought-severe drought and severe drought-extreme drought were 0.09, 0.07, and 0.06, respectively. [Conclusion] WUE can well reflect the ecological drought sensitivity of vegetation under drought stress during the growing period and can be used as a factor to characterize ecological drought sensitivity. [ABSTRACT FROM AUTHOR]