Differential impact of flash droughts on water use efficiency in terrestrial ecosystems in Central Asia

In the context of climate warming, the rising risk of flash droughts in Central Asia (CA) remains inadequately understood in terms of their specific impacts on diverse regional ecosystems. Hence, this study employs the Evaporative Demand Drought Index (EDDI) and the rate of soil moisture (SM) intensification to identify varying evaporative demand flash droughts (EDFD) and SM flash droughts (SMFD) in CA. It analyzed spatiotemporal patterns and trends of eco-hydrological factors (e.g., SM, potential evapotranspiration (PET), actual evapotranspiration (AET), gross primary productivity (GPP), and water use efficiency (WUE)), explored the characteristics of flash droughts, and examined the differential responses of WUE to flash droughts across different terrestrial ecosystems in CA. The findings indicated that: (1) SM was notably higher in the western and southeastern CA, with a significant upward trend in the northwestern and central-eastern CA. GPP and WUE significantly increased in central-eastern and southwestern CA (p < 0.05). (2) High-intensity EDFD and SMFD events (e.g., EDFD_95 and EDFD_98) frequently occurred in the northern and southeastern CA, with averaging more than 30 occurrences and durations typically extending beyond 2 pentads. (3) In central, western, and southwestern CA, GPP increased following weaker flash droughts but decreased after more severe ones. Agricultural areas showed heightened sensitivity to these changes. However, WUE generally improved with increasing flash drought intensity. WUE of cropland in CA had the highest sensitivity to flash drought. Understanding the responses of diverse ecosystems to flash droughts is essential for the sustainable management of ecological and water resource systems.