Evaluation of ecological drought in northwest China by integrating ecological water budget and vegetation status.

Abstract

Global warming is increasing the frequency and intensity of drought events, posing profound threats to ecosystems. Ecological drought is a multifaceted process in terrestrial ecosystems, characterized by the impairment of vegetation eco-physiological functions due to water stress. However, current ecological drought assessments primarily focus on ecological water supply and demand, often overlooking the status of vegetation growth. To address this gap, we developed a standardized composite ecological drought index (SCEDI) that integrates precipitation (Pre), ecological water deficit (EWD), and the vegetation health index (VHI) using a Euclidean distance-based approach. We further analyzed spatiotemporal dynamics of ecological drought and its characteristics, utilizing run theory and empirical orthogonal function (EOF) methods. Results showed that ecological drought intensified in spring (SCEDI change: -0.002) and winter (-0.013), but weakened in summer (0.006) and autumn (0.002). The first EOF mode explained 30.51 % of the total variance, indicating a reversal in wet-dry patterns between mountainous regions and oases around 2002. Over the past 34 years, Xinjiang has experienced more than 19 ecological drought events, each with an average duration of approximately 3.11 months. Regionally, droughts in mountainous areas occurred more frequently but were shorter and less intense, while in oasis areas they were less frequent but more persistent and severe. Furthermore, Shapley Additive Explanations (SHAP) analysis identified EWD (SHAP value: 0.265) and precipitation (0.176) as the most influential drivers of ecological drought. Higher values of both factors were positively associated with ecological drought severity, while lower values had a mitigating effect. This study highlights the potential of SCEDI in accurately capturing ecological drought dynamics and provides a scientific basis for ecological risk assessment and adaptive drought management in arid regions.