Picture: Drought near Armidale. Credit: Tatiana Gerus (CC BY-NC-ND 2.0)
Flash drought is a type of drought that is characterised by a rapid onset and intensification and with substantial impacts on agriculture. In a matter of weeks, regions with lush green and healthy crops can find themselves in a severe drought, jeopardising the annual harvest and livestock as reported in the 2012 flash drought in the US mid-west, 2015 in western Victoria and more recently in southern Queensland in 2019.
Flash drought has been assessed using case studies as those mentioned above to understand the processes involved that cause rapid drying conditions in the upper soil moisture. Direct soil moisture measurements are rarely employed in drought indices because in situ soil moisture observations are sparse in space and time. Instead, proxies that reflect moisture supply and demand, such as precipitation and evaporation, are commonly used. The general consensus in flash drought research is that it is a combination of strong precipitation deficits and increased evaporation that triggers flash drought development. The relative contributions of each vary depending on the climate regime of interest.
Until now, flash drought research has been on the regional scale and has been limited to observations and reanalyses. CLEX researchers have been the first to examine flash drought in climate models. Specifically, we have examined how climate models simulate flash drought and how models represent flash drought processes to allow for assessment in a changing climate. The work compares the skill of drought indices based on precipitation, evaporative demand, an estimate of evaporation, and a combination of evaporative demand and actual evaporation for flash drought early detection on a global scale. The results show that all drought indices show a higher frequency of flash drought events, particularly those based on precipitation or evaporative demand alone compared to the models’ soil moisture. Precipitation deficits are the main contributor to flash drought in climate models, with evaporation playing a secondary role. However, an overestimation of evaporative demand in some models causes significant inter-model disagreement, reflecting differences in the representation of land-atmosphere interactions.
- Paper: Hoffmann, D., Gallant, A. J. E., & Hobbins, M. (2021). Flash Drought in CMIP5 Models, Journal of Hydrometeorology, . Retrieved Apr 12, 2021, from https://journals.ametsoc.org/view/journals/hydr/aop/JHM-D-20-0262.1/JHM-D-20-0262.1.xml