Using Seasonal Evaporative Stress Across Europe to Identify Areas Primed for Flash Drought

Anthropogenic climate change is expected to increase the frequency and intensity of climactic extremes across Europe. With rising temperatures, the impacts of a severe flash or prolonged agricultural drought could yield devastating financial costs. As such, indicators that predict future drought could mitigate risk and damage. This study explores the seasonal and inter-seasonal relationships between atmospheric and terrestrial variables and flash drought occurrence using linear regression and correlation analysis. Data from NASA MERRA-2, between 1980 and 2020, were used for temperature, ET, PET, and soil moisture. ET and PET were used to derive the Standardized Evaporative Stress Ratio (SESR), which is a metric that incorporates several near-surface state variables to represent evaporative stress on the environment. The results show that higher mean temperatures lead to increased evaporative stress and reduced root zone soil moisture (RZSM) throughout much of Europe during spring, summer, and fall. Correlation values yielded a strong negative relationship consistent with the known characteristics between temperature, evaporative stress, and soil moisture. Further, lag-regression analysis between subsequent seasons demonstrated strong negative correlations for mean temperature and mean SESR ratio with RZSM for both a spring-summer and summer-fall seasonal lag across much of the European continent. In addition, many of these correlations show statistical significance above 95%. A multivariable regression indicates that the interaction of SESR and RZSM is stronger than that of T and RZSM, and that SESR is the predominant driver of subsequent season RZSM levels. This validates SESR as a possible predictor for flash drought. Finally, comparison with known flash drought events in Europe yields that increases of seasonal temperature and evaporative stress can indicate areas primed for flash drought development in the following season.