Heat and drought extremes are now occurring simultaneously

Although a future increase in heat and drought is inevitable across some regions, the specifics are a little harder to nail down, especially in how the two phenomena will interact with each other. New research has investigated the circumstances under which droughts and heat waves will occur simultaneously. These double whammy weather extremes are known as  “compound hot-dry events.”

Scientists from the Helmholtz Centre for Environmental Research – UFZ defined droughts as periods which were drier than 90 percent of the year, and heat events as periods which were hotter than 90 percent of the summer season. 

“In the past, periods of drought and heat waves were often considered separately; there is, however, a strong correlation between the two events, which can be seen in the extremes experienced in 2003 and 2018 in Europe. The negative consequences of these compound extremes are often greater than with one single extreme,” said UFZ climate researcher Dr. Jakob Zscheischler.

The experts used a new modeling technique that produced more precise and telling conclusions than previous studies. The researchers used seven climate models and ran each model 100 times for different scenarios that represented natural variation. 

The scientists then looked closely at the historical record for 1950 to 1980, and compared this climate to a future one with a two-degree increase from pre-industrial temperatures.  

“The advantage of these multiple simulations is that we have a much larger volume of data than with conventional model ensembles, enabling us to better estimate compound extremes,” explained study first author Dr. Emanuele Bevacqua.

The scientists found that compared to the time frame from 1950 to 1980, the frequency of hot-dry events will increase by four fold in a future with a two-degree temperature increase. The researchers also discovered that the deciding factor for hot-dry events is precipitation. This is because, as temperatures rise, every drought will be accompanied by extreme heat.    

“This demonstrates that local precipitation trends determine whether periods of drought and heat waves will occur simultaneously,” explained study co-author Emanuele Bevacqua. 

The research is a step towards understanding the complexity of climate change and hopefully will help improve strategies for preparation and adaptation. 

The study is published in the journal Nature Climate Change.

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By Zach Fitzner, Earth.com Staff Writer