Precipitation Trends Influence How Often Droughts, Heat Waves Occur Together

Scientists have observed that the occurrence of droughts and heatwaves at the same time has become more common in recent years. Now, a team of researchers has found that precipitation is mainly responsible for this phenomenon.

Dry Soil Due to Heatwave

Dry Soil Due to Heatwave

The new study breaks ground on the factor that could be used to predict the simultaneous occurrence of the two extreme events in the future. Existing models were associated with high uncertainties that the estimated occurrences could not be relied on so much.

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Climate researchers from the Helmholtz Centre for Environmental Research (UFZ) have found that the future frequency of simultaneous episodes of droughts and heatwaves – a phenomenon scientists call compound hot-dry events – will depend mainly on local precipitation trends. This is based on an assumed two-degree rise in global temperature due to global warming.

The research, which appeared in Nature Climate Change, can help in improving adaptation to climate change risks.

Concurrent extreme events

Simultaneous occurrence of both droughts and heat waves can have very unpleasant events on humans, animals, and the environment. Each event is capable of causing serious problems when occurring singly, let alone when they occur at the same time as the other.

These events can result in considerable crop losses and wildfires, among other challenges. The frequency of their occurrence together has been increasing in recent decades.

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

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Researchers defined compound hot-dry events as summers with average temperature readings higher than 90 percent of the summers from 1950 to 1980 and precipitation levels that were at the same time lower than in 90 percent of those summers.

With the ongoing global warming and climate change, it is expected for temperatures on land to increase and for average precipitation to change. This will, in turn, cause more droughts and heatwaves.

The conditions that would promote the concurrent occurrence of the two events were not fully known before now, however. That’s what the current research was intended to shed more light on.

Precipitation at work

Scientists in this study made use of a novel model collection that combines seven climate models. This helped to reduce uncertainties often seen with climate model simulations and aided in understanding them better.

Covering the period from 1950 to 1980, the team performed each model simulation as many as 100 times. This was done to explain natural climate variation.

The scientists compared their results with what could obtain in a future climate with an assumed two-degree higher temperature than in preindustrial conditions. According to them, the average frequency of simultaneous occurrence of droughts and heat waves will increase to about 12 percent in the future climate. The frequency was only 3 percent between 1950 and 1980.

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Furthermore, the UFZ researchers found that precipitation trends, not temperature, will determine the future incidence of compound hot-dry events. This is because only a two-degree rise in temperature will be enough to cause droughts anywhere in the world to occur alongside heat waves, they said.

The predicted global effects due to a temperature rise will occur regardless of the extent of the increase in local temperatures.

The finding that precipitation plays a higher role can help humans to improve risk adaptation to climate change. It will also aid in better understanding the effects of long-term climate transformation.

This discovery may also be applied to other compound extreme events, the researchers said. It could, for instance, be used to understand the link between tropical storms and heatwaves.

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Precipitation trends determine future occurrences of compound hot–dry events



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