Shift to 'flash droughts' as climate warms

The research published in Science shows that flash droughts, which start and develop rapidly, are becoming 'the new normal' for droughts, making forecasting and preparing for their impact more difficult.

Flash droughts can develop into severe droughts within a few weeks. They are caused by low precipitation and high evapotranspiration, which quickly depletes the soil of water. While they start quickly, the droughts can last for months, damaging vegetation and ecosystems, and triggering heat waves and wildfires.

A multinational group of researchers wanted to understand if there had been a transition from conventional 'slow' droughts to flash droughts and how this trend will develop under different carbon emission scenarios.

"Climate change has effectively sped up the onset of droughts," says Professor Justin Sheffield, Professor of Hydrology and Remote Sensing at the University of Southampton and co-author of the paper.

"While it varies between different regions, there has been a global shift towards more frequent flash droughts during the past 64 years."

The transition to flash droughts is most notable over East and North Asia, Europe, the Sahara, and the west coast of South America. Some areas, such as eastern North America, Southeast Asia and North Australia, saw fewer flash and slow droughts, but the speed of drought onset had increased. In the Amazon and West Africa, there was no evidence of a transition to flash droughts; the Amazon saw an increase in slow droughts and West Africa saw an increase in the frequency and extremity of both fast and slow droughts.

Professor Justin Sheffield added: "As we head towards a warmer future, flash droughts are becoming the new normal. Our models show that higher-emission scenarios would lead to a greater risk of flash droughts with quicker onset which pose a major challenge for climate adaptation."

The transition to flash droughts may have irreversible impacts on ecosystems as they may not have enough time to adapt to a sudden lack of water and extreme heat. Forecasting flash droughts is also difficult as current approaches to predicting droughts use longer time scales.

The researchers say new approaches are needed to provide early warnings of flash droughts, as well as a better understanding of how natural ecosystems and humans will be impacted.

Funding for the research was provided by the National Natural Science Foundation of China, the National Key R&D Program of China, the Natural Science Foundation of Jiangsu Province for Distinguished Young Scholars, and the UK-China Research & Innovation Partnership Fund through the Met Office Climate Science for Service Partnership (CSSP) China as part of the Newton Fund.