Assessing the impact of drought on water use efficiency among ecosystems on the Mongolian Plateau

Water use efficiency (WUE) encompasses precipitation use efficiency (PUE), soil water use efficiency (SWUE), and groundwater use efficiency (GWUE) and serves as a key indicator for evaluating ecosystem responses to drought, particularly as climate change continues to intensify. This study investigates the responses of various WUE indicators to drought conditions on the Mongolian Plateau at a spatial resolution of 0.1° from 2000 to 2020. Drought conditions are measured using drought indices such as the Standardized Precipitation Evapotranspiration Index (SPEI), Soil Moisture Anomaly Index (SMAI), and Groundwater Storage Deficit Index (GWSDI). The findings reveal that while PUE, SWUE, and GWUE generally exhibited upward trends, their responses to drought varied significantly. In arid regions, WUE indicators showed positive correlations with drought indices, while in humid regions, negative correlations were observed. The SPEI and SMAI predominantly indicated a wetting trend, whereas GWSDI reflected a drying trend across most of the study area (67.47%). Moreover, the study identified lagged effects of drought on PUE, SWUE and GWUE that ranged from 2.4 to 4.4 months and varied according to vegetation type and climatic region. Although drought typically led to reductions in PUE and SWUE, enhancements of GWUE were observed in both semi-humid forests and semi-arid sandy lands under groundwater drought. Given the Mongolian Plateau's ecological fragility and its critical role in East Asia's water and carbon cycles, these findings underscore the complexity of drought impacts on WUE and highlight the need to develop appropriate ecosystem management strategies to address the challenges posed by climate change.