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‘Flash drought’ will increase over humid regions in the future

by TR Pakistan

Rapidly developing intraseasonal drought events, termed as “flash droughts,” are a new phenomenon with increasing prominence under global warming. It develops rapidly without sufficient early warning, and has resulted in severe impacts around the world in recent years.

In 2012, the droughts over central United States caused billions of dollars in economic losses while the following year in southern China, it affected two million hectares of crops in Guizhou and Hunan provinces alone. This has prompted scientists to investigate flash drought risk and its underlying drivers in a changing climate on an urgent basis.

“Still, how will the flash drought risk change in a warming future climate remains unknown for a number of reasons,” said Xing Yuan from the Nanjing University of Information Science & Technology. “For example, there’s a diversity of flash drought definition that scientists haven’t agreed upon, the role of anthropogenic fingerprints is not clear, and we are not sure of future socioeconomic scenarios.”

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Yuan and his PhD students Linying Wang, Peng Ji and Miao Zhang from the Institute of Atmospheric Physics at Chinese Academy of Sciences, Dr. Peili Wu from the UK Metropolitan Office and Professor Justin Sheffield from the University of Southampton, have addressed these issues in a recently published study in the academic journal Nature Communications.

The study focuses on China where rapid industrialization and urbanization have significantly increased environmental vulnerability under global warming. The researchers have proposed a new definition of flash drought based on rapid decline rate of soil moisture and the dry persistency. This new definition captures both the “flash” and “drought” characteristics and the authors of the paper have also proposed a new method for explicitly characterizing flash drought events.

“We carried out land surface ensemble simulations driven by multiple climate models under different external forcings such as greenhouse gases,” explained Yuan. Their results show a significant increasing trend of flash drought frequency over China during 1961-2005, with a clear 77% footprint from anthropogenic greenhouse gas emissions.

Under moderate emission scenarios, the exposure risk in China will increase by 23% in the middle of this century. This increase can reach up to 40% in the southern provinces with a humid climate such as Guizhou, Guangxi, Guangdong and Zhejiang, while the exposure risk in semi-arid northern areas in China will decrease.

“This indicates that anthropogenic climate change has changed the traditional arid areas, and more attention should be paid to deal with the flash drought risks in humid and semi-humid areas,” stated Yuan. The study found that population increase was also an important factor for enhancing the exposure risk of flash drought over southernmost humid regions.

Their results suggest that the traditional drought-prone regions in China would expand given the human-induced intensification of flash drought risk.

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