Disastrous duo: Heatwaves and droughts 

Climate change is at the heart of more frequent and intense dry and hot extremes in recent decades as simultaneous heatwaves and droughts are becoming increasingly common in western parts of the United States, according to a new study led by researchers from McGill University in Montreal, Canada.

_{The researchers suggest that periods of dry and hot weather, which can make wildfires more likely, are becoming larger, more intense and more frequent because of climate change. Image: Anat Chantrakool/123rf}

In a study published by Science Advances, the researchers analysed heat and drought events across the contiguous United States over the past 122 years. They found that combined dry and hot events have not only increased in frequency, but also in geographical size. Where such events were once confined to small parts of the United States, they now cover whole regions such as the entire west coast and parts of the Northeast and Southeast.

“Dry-hot events can cause large fires. Add wind and a source of ignition, and this results in ‘megafires’ like the 2020 fires across the west coast of the United States. Drought and record-breaking heatwaves, coupled with a storm that brought strong winds and 12,000 lightning events in a span of 72 hours, caused more than 500 wildfires,” says the study’s lead author Mohammad Reza Alizadeh, a PhD student under the supervision of Professor Jan Adamowski in the Department of Bioresource Engineering at McGill University.

The researchers also found that dry and hot weather events are intensifying, with longer periods of drought and higher temperatures. These dual “dry-hot extremes” are not only self-intensifying – more heat causes more drought and vice versa – but they are also self-propagating. This means that they are able to move from region to region. “As increased temperatures are driving and expanding aridity, droughts and heatwaves move from one region to downwind regions,” says Alizadeh. These extremes can be particularly damaging for agricultural production and ecosystems, they warn.

According to the researchers, the trigger for these hot-dry events is shifting. Looking back at the catastrophic Dust Bowl of the 1930s, they explain that the dust storms were driven by a lack of rainfall coupled with poor land management practices. However, in recent decades dry-hot disasters have been driven more often by excess heat than by a lack of rainfall.

The researchers caution that the future will bring us more of these disasters, if the current warming trends continue. They suggest that their findings could be used to inform climate mitigation and adaptation efforts. “We need to understand how things are changing in order to adapt,” says Professor Jan Adamowski.

Read the study here