Inter-seasonal terrestrial-atmospheric drivers of flash drought over Europe

Anthropogenic climate change is expected to increase the frequency and intensity of climactic extremes across Europe. With rising temperatures, the impacts of a severe 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 land surface variables using linear regression and correlation analysis. Data from 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. It is shown through regression modeling that higher mean temperatures lead to increased evaporative stress and reduced root zone soil moisture 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 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 90%. Finally, this study identified a similar relationship between root zone soil moisture with temperature and SESR yielding correlation at elevated levels of statistical significance indicating that springtime temperature may be a critical precursor to growing season flash drought development.