Utility of the standardized precipitation evapotranspiration index (SPEI) to detect agricultural droughts over China

Abstract

Study regionChina.Study focusMeteorological drought indices, such as the Standardized Precipitation Evapotranspiration Index (SPEI) have been widely used as a proxy for soil moisture to study agricultural droughts. However, the SPEI and soil moisture are driven by different factors, which may lead to inconsistencies or even contradictions under certain circumstances, and the utility of the SPEI to represent soil moisture remains poorly understood. This study systematically evaluated the performance of the SPEI to detect agricultural droughts using two recently developed high-resolution datasets over China.New hydrological insights for the regionThe SPEI and soil moisture exhibit a strong correlation across eastern China, though notable seasonal variability is present. For near-surface soil, the correlation time scale is typically within three months, which increases with soil depth and towards the northwest. The time scale is shorter in autumn and longer in spring. Over 60% of China shows consistent trends between the SPEI and soil moisture. However, the SPEI may fail to detect agricultural droughts in the northwest and may incorrectly identify droughts in the southeast. Consequently, the usability of the SPEI for detecting agricultural droughts varies by region and season, highlighting the need for future studies to evaluate its utility prior to its direct application.

Keywords

• Drought index
• Soil moisture
• Correlation
• Trend