Delving into flash droughts in Vietnam during the last two decades using the standardized evaporative stress ratio

Abstract

A flash drought is a recently defined extreme event that has destructive impacts on agriculture as well as other elements of society and ecosystems. Understanding where and when flash droughts occur can improve predictability and mitigation strategies for countries with economies that rely on agriculture. This study represents the first investigation of flash drought occurrences in Vietnam, one of the largest agricultural exporters in the world, using the standardized evaporative stress ratio (SESR). Monthly SESR data captured historical sustained drought events across the study period and exhibited a pattern similar to that shown by the standardized precipitation evapotranspiration index over most of the study region, with Pearson’s correlations mostly ranging from 0.52 to 0.82. Results of the SESR analysis at a pentad timescale indicate that flash droughts did occur in the country over the last two decades, with the northern regions and a majority of the south-central coast experiencing fewer than 9 flash drought events that covered less than 20% of each region. The remaining southern areas of the country were subjected to a much higher flash drought frequency, with 12 to 21 occurrences covering from 30% to more than 50% of the area in each region, typically during the dry season and exacerbated by anomalies of potential evapotranspiration and temperature. This research also revealed that flash droughts in Vietnam were correlated with the El Niño Southern Oscillation climate phenomenon, particularly in the southern regions, where a high flash drought frequency could take place under either El Niño or neutral conditions. This study provides new evidence to support the development of a comprehensive overview of drought in Vietnam, the country’s drought mitigation strategies, and water management policies.