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Abstract
Flash drought is the rapid onset or intensification of short-term agricultural drought. This research aimed to quantify the frequency and duration of flash drought and its effect on rainfed maize (Zea mays) and cotton (Gossypium hirsutum L.) yields in the southeastern United States. For this study, a flash drought event was defined as when root zone plant-available soil water was less than 40% of field capacity for 15 consecutive days during the growing season. The SmartIrrigation (SI) CropFit App was used to quantify flash drought events at 40 virtual rainfed cotton and 61 virtual rainfed maize fields in Florida and Georgia from 2003-2022 during the growing season and the crops’ reproductive phase. Overall, Georgia experienced more flash droughts than Florida. The Decision Support System for Agrotechnology Transfer (DSSAT) CSM-CERES-Maize and CSM-CROPGRO-Cotton crop simulation models were then used to simulate yield reductions resulting from a 15-day flash drought during different phenological stages of cotton and maize at selected virtual fields. Simulated maize yield reductions exceeded 40%-50% in Coastal Plain regions in Georgia and Florida for a 15-day flash drought event during the first half of June. The maximum cotton yield reductions were approximately 25% for events occurring from mid-July to mid-August. For SI CropFit to be used to quantify flash drought for forage grass as was done for cotton and maize, it requires a forage grass model with a region-specific crop coefficient (KC) curve. The DSSAT CSM-CROPGRO-Perennial-Forage model was applied to develop a KC curve for rainfed forage bermudagrass in southern Georgia. The model was evaluated using three years of field data and then used to simulate daily KC values for three years. A KC was developed by fitting a polynomial curve to the simulated KC values. This curve can be integrated into SI CropFit as it represents the expected crop water use patterns of optimally managed rainfed forage bermudagrass in southern Georgia. Overall, this entire study, for the first time, quantified the frequency of flash drought and its effects on crop yield in the southeastern U.S. and provides a methodology for capturing the occurrence of flash drought in real time.