Discovery Files

Climate change impact on extreme weather events

Scientists investigated the effects of climate change on the intensity, frequency, and duration of extreme weather events

In a paper published in Proceedings of the National Academy of Sciences, scientists investigate the effects of climate change on exacerbating compounding heat and drought situations.

The U.S. National Science Foundation-supported findings offer new insights into predicting their interplay, which will provide scientists and policymakers with a clearer and more holistic approach to preventing and preparing for extreme weather events.

The researchers document the effects of increasingly severe droughts and wildfires in the past three years. "Research on climate change continues to underscore serious impacts that are being experienced nationally and globally," says Bruce Hamilton, a program director in NSF's Directorate for Engineering.

"Two standout events," says Michael Mann of the University of Pennsylvania, "were the 2020 California wildfires and the 2019–20 Australian bush fire season, which lasted nearly one whole year. These are known as compound drought and heat wave events and refer to situations wherein a region experiences both prolonged hot temperatures and a shortage of water."

These conditions can occur together and worsen each other's impacts, the researchers say, and could potentially lead to heat-related illnesses and deaths, water scarcity for drinking and agriculture, reduced crop yields, increased wildfire risk and ecological stress. They also note that anthropogenic climate change — climate change that is driven by human activity — can contribute to the frequency and severity of these events. 

The researchers compared two contrasting socioeconomic pathways: the high-end or worst-case scenario, wherein society fails to mitigate the effects of anthropogenic climate change, and a moderate scenario, wherein some conservative measures are put in place and efforts are made to abide by them.

In the worst-case scenario, they found that by the late 21st century approximately 20% of global land areas are expected to witness approximately two compound drought and heat wave (CDHW) events per year. These events could last for around 25 days and have a fourfold increase in severity.

"Comparatively, the average CDHW frequency over the recent observed reference period was approximately 1.2 events per year, lasting less than 10 days, with far less severity," Mann says.

The most vulnerable geographical regions, such as eastern North America, southeastern South America, Central Europe, East Africa, Central Asia, and northern Australia, are projected to experience the largest increases in CDHW frequency by the end of the 21st century.

"Interestingly, places like Philadelphia and some of the regions in the eastern U.S. are where we expect to see an increase in these sorts of events; urban environments in the summertime will witness the highest relative frequency of these events," Mann says.