‘Flash’ droughts, which can develop in as little as two weeks, are becoming increasingly frequent in many regions - causing severe and sudden impacts on agriculture, ecosystems and economies. However, they are extremely hard to predict.
Now, scientists at the UK Centre for Ecology & Hydrology (UKCEH) have made a key finding that could transform forecasting, providing communities with time to take action to mitigate the impacts on food production, the spread of wildfires and human health.
The study of 20 years of data in Africa has revealed that vegetation growth was visibly affected one-two months before the onset of flash droughts - and this can be detected via satellite observations. With little ground-based monitoring done in many parts of the world, remote observations would enable scientists to better forecast these extreme events.
Dr Bethan Harris, a land-atmosphere scientist at UKCEH who led the study, says flash droughts are caused by a combination of low rainfall with warm, dry air in the area above the soil that increases evaporation, causing a ‘feedback loop’. The drying of the soil makes air warmer which then further dries out the soil, further warming the air which in turn further dries the soil, and so on.
Regions where changes in soil moisture more strongly affect air temperature, such as the Sahel or the central USA, are particularly prone to flash droughts.
Providing more warning
Dr Harris said: “Usually, droughts take several months to develop, as we have seen in the UK this year, allowing farmers, water companies and authorities to take some action to mitigate the impacts of the extreme weather.
“But flash droughts can develop very quickly, with some areas going from having relatively normal soil moisture to exceptionally dry soils in just a few weeks. These events can result in crop failures – reducing regional and global food security – as well as insufficient clean drinking water and more heatstroke cases because hotter weather is associated with flash droughts.
“Existing computer models only correctly forecast around 30% of flash droughts a week in advance, and the lack of warning and certainty in these predictions does not enable communities to plan ahead effectively.”
More time to prepare for flash droughts would, for example, enable:
- Farmers to set up irrigation or plant different crops.
- Land managers to clear dry vegetation to reduce the risk of wildfires spreading.
- Health authorities to divert medical care resources to areas where there are likely to be more heatstroke cases.
Vegetation provides clues
Scientists say flash droughts are increasing in frequency across many regions and will rise further under future global warming due to lower rainfall and increases in evaporation. However, global research into flash droughts is at a relatively early stage.
The condition of vegetation – both the growth of leaves and wood and the amount of water in them –provide important telltale sign of how severe an upcoming drought could be. These factors can be measured by analysing satellite-derived data but are not currently incorporated in forecasting models for flash droughts.
Dr Harris said that while more research and development of modelling techniques are needed, automated monitoring of vegetation to provide early warnings of a flash drought would be possible.
The study, which involved UKCEH, TU Wien and the University of Leicester, has been published in the journal Hydrology and Earth System Sciences.
Paper information
Harris et al. 2025. Global observations of land-atmosphere interactions during flash drought. Hydrology and Earth System Sciences. DOI: 10.5194/hess-29-6917-2025. Open access.
The work was produced as part of a European Space Agency Climate Change Initiative Research Fellowship awarded to Bethan Harris.