Global Flash Drought Analysis: Uncertainties From Indicators and Datasets

Flash Drought (FD) has garnered much attention in recent years, with significant advancements in the indicators applied for identifying these rapidly intensifying events. However, the difference in existing FD definitions and methodologies among research communities and the choice of different data sources underscores the importance of addressing the uncertainties associated with the global FD characteristics and their drivers. This study compares two key FD indicators derived based on evaporative stress ratio (ESR) and root-zone soil-moisture (RZSM) using three different data sources to investigate the uncertainties in global FD frequency and intensity (speed), and the influencing drivers. The results suggest that such disparities are significant in the two FD indicators across different climate regions of the globe. The results highlight varying spatial drivers of FD frequency, intensity, and their evolution, potentially linked to background aridity. Changes in precipitation, temperature, vapor pressure deficit, and soil-temperature coupling play an important role with a cascading (concurrent) impact on the evolution of FD based on RZSM (ESR). The relationship between ESR and RZSM fails to explain most of the variance in each of these indicators specific to the FD episodes, especially in the transitional and humid climate regimes. Overall, the results highlight the necessity of more nuanced methodologies for deriving FD indicators that can efficiently couple the rapid soil-moisture depletion rates in deeper layers with changes in atmospheric evaporative demand which has direct implications on vegetation health.

Automated summary

Flash drought (FD) has received significant attention, but the differences in FD definitions and methodologies, as well as the choice of data sources, highlight the uncertainties in global FD characteristics. This study compares two key FD indicators and finds significant disparities across different climate regions. The results highlight the spatial drivers of FD frequency, intensity, and their evolution, potentially related to background aridity. Changes in precipitation, temperature, vapor pressure deficit, and soil-temperature coupling play important roles in the evolution of FD. Overall, the results emphasize the necessity of nuanced methodologies for deriving FD indicators that can couple rapid soil-moisture depletion rates with changes in atmospheric evaporative demand, which has direct implications for vegetation health.