Detection of agricultural flash droughts using impact-informed thresholds

Abstract. A rapid and sustained evaporative stress causes soils to lose moisture within days to weeks during sensitive crop phases. This rapid soil depletion can severely affect agricultural systems and manifest as events commonly referred to as agricultural flash droughts (AFDs). AFDs are often detected using literature-based thresholds that assume uniformity across time and space. This may, however, poorly represent the occurrence and impacts of AFDs in local contexts and limit usefulness to decision-makers who require context-specific information. This study aims to overcomes these limitations by introducing an impact-informed calibration of the Standardized Evaporative Stress Ratio (SESR) by linking SESR thresholds to observed crop losses. Thresholds are derived temporally across crop management periods and spatially across soil textures. The proposed calibration approach is tested in Nicaragua’s Dry Corridor of Central America, where rainfed agriculture predominates. Results suggest that although SESR exhibits coherent evaporative stress signals during years with drought-induced crop losses, literature-based thresholds showed limited skill in translating these signals into agriculturally relevant flash drought detection across different crop management periods and soil textures. Threshold performance varies across crop management periods and soil textures. Reliable thresholds could not be detected in sandy soils, whereas clay-rich soils exhibited stable and skilful thresholds. In loamy–silty soils, skilful thresholds were mainly observed during March and the pre-sowing period, with limited skill thereafter. Validation results also showed that calibrated thresholds, within the crop periods-soil combinations identified as skilful, successfully detected flash drought events associated with crop losses more frequently than those reported in the literature. Together, these findings indicate that monitoring AFD using impact-informed thresholds has an operational value for drought management and can support better decision-making.