Hotspots for flash drought occurrence in South America

MIGUEL A. LOVINO; ERNESTO H. BERBERY; OMAR V. MÜLLER; MARÍA JOSEFINA PIERRESTEGUI; GABRIELA V. MÜLLER

Conferencia; 13th International Conference on Southern Hemisphere Meteorology and Climatology; 2022

Flash droughts (FD), characterized by rapid soil drying, can negatively impact livestock and crop yields. We propose a novel FD definition based on root-zone soil moisture (SM) and soil hydraulic properties. The index is tested over South America to identify regions prone to FD. We employ ERA5 1-m root-zone SM pentad data for the 1950-2020 period complemented with the ERA5 field capacity and wilting point volumetric soil moisture values. We define an FD when the Soil Water Deficit Index (SWDI) decays from -3 to -5 in 4 pentads. We also require that the SM depletion lasts at least 3 pentads to exclude those short events that deplete SM rapidly down but then recover up suddenly. We detect FD hotspots by counting the total number of FD events during the whole year over the 1950–2020 period. To determine the spatial pattern of changes in FD occurrence, we estimate linear trends in time series of the number of FD events per year. We apply the Mann–Kendall test to detect significant trends at the 5% significance level.We find that several regions in South America that are most beneficial for agriculture are also the hotspots for FD occurrence, including croplands and grasslands over the Pampas region in southeastern South America, northern Colombia, and northern Venezuela – central Colombia. FD increased in most of South America between 1950 and 2020. The most significant upward trends occurred in parts of the hotspots for FD occurrence, namely southern Brazil, northern Colombia, and northern Venezuela.