'Flash droughts', or droughts that start and develop rapidly, have become more frequent due to human-caused climate change and the trend is predicted to accelerate in a warmer future, according to a new research.
An international team of researchers, including those from the University of Southampton, UK, said that flash droughts are fast becoming the 'new normal' for droughts, making forecasting and preparing for their impact more difficult. Their research is published in the journal Science.
Flash droughts, caused by low precipitation and high evapotranspiration and leading to quick depletion of soil of water, can develop into severe droughts within a few weeks. While they start quickly, the droughts can last for months, damaging vegetation and ecosystems, and triggering heat waves and wildfires.
The researchers wanted to understand if there had been a transition from conventional 'slow' droughts to flash droughts and also how the trend would develop under different carbon emissions scenario. The researchers found that the transition was most notable over East and North Asia, Europe, the Sahara, and the west coast of South America.
They said that while some areas, such as eastern North America, Southeast Asia and North Australia, saw fewer flash and slow droughts, the speed of drought onset had increased.
"Climate change has effectively sped up the onset of droughts," said Justin Sheffield, professor of Hydrology and Remote Sensing at the University of Southampton and co-author of the paper.
Further, they found that while the Amazon saw an increase in slow droughts, West Africa saw an increase in the frequency and extremity of both fast and slow droughts. "While it varies between different regions, there has been a global shift towards more frequent flash droughts during the past 64 years," said Sheffield.
"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," said Sheffield.
The transition to flash droughts, the researchers said, could have irreversible impacts on ecosystems owing to their inability to adapt to a sudden lack of water and extreme heat. Current approaches to predicting droughts use longer time scales, making forecasting flash droughts difficult.
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.
