Flash droughts are short dry spells replacing slower onslaughts, making them harder to predict
The last six decades have recorded a transition towards ‘flash droughts’ in 74 per cent of the global regions, mainly due to human-induced climate change, according to a study published in journal Science.
Under high-emission scenarios, the onset speed of droughts is also expected to increase. Flash droughts are short dry spells replacing slower onslaughts, making them harder to predict.
As opposed to the gradual onset of a slow drought lasting months or even years due to large-scale climate patterns like El Nino, the effects of a flash drought can be seen within days or weeks.
The scientists analysed the soil moisture data between 1951 and 2014 and included spells that lasted 20 days or longer. This excluded spells that were too short to cause any significant damage. They calculated the rate at which the soil dried up during the initial period of drought.
Heatwaves during flash droughts are also more intense than seasonal ones. These have been recorded more in tropical regions like Sub-Saharan Africa, Southeast Asia, the western coast of South America, Southern Australia and the Amazon basin.
In future, this could have disastrous consequences, especially for farmers in these regions who depend on rain-fed agriculture, since abrupt dry spells could damage crops and compromise the country’s food security.
Xing Yuan, a hydrologist at Nanjing University of Information Science and Technology in China and the study’s lead author, said the onset speed has been increasing even for slower droughts.
Interest in flash droughts has increased over the last decade, especially after the United States faced its worst drought in over half a century in the summer of 2012.
Many affected areas transformed from normal to extreme drought conditions within a month and none of the climate models were able to predict it. This led to over $30 billion in losses.
Last year, China’s Yangtze River was struck by a flash drought due to high temperatures that developed within a month and triggered wildfires. Parts of southern China faced energy shortages due to this because there was no hydropower.
In the tropics, the rainy seasons maintain moisture in soil and vegetation. But when rains fail unexpectedly, the equatorial heat can desiccate the ground beyond expectation. Flash droughts can give humans little time to adapt, like diverting water sources or controlling wildfires.
Yuan says that monitoring systems will need to be improved in the near future because current systems often cannot capture drought onsets at short enough time scales.
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