Forcasting When Heat Waves Turn Deadly

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Some of the biggest weather disasters can arrive in the middle of the night, not as a storm, but as a stillness. Atmospheric conditions that were first welcomed for their clear skies and sunny summer days can go from good to bad to worse.

This is the scenario that played out over Russia and eastern Europe last summer, when an estimated 56,000 people died, crops failed and more than 600 wildfires scorched the landscape and filled the sky with choking smog. And it happened in 2003 over western Europe, when at least 25,000 and potentially as many as 70,000 succumbed to heat-related causes.

NEWS: Summer Heat Waves to Increase

According to two recent studies published in Geophysical Research Letters, some heat waves like 2003 have the earmarks of climate features such as a warming trend or sea surface temperatures or ice cover to use as potential clues for seasonal outlooks, but others, like Russia 2010, are creatures of natural atmospheric variation which is not nearly so congenial to prediction beyond the brief timescale of weather.

While global climate models see heat waves becoming more frequent and intense as the atmosphere takes on more greenhouse gases, weather forecast models are not very good at predicting the comings and goings of atmospheric blocking patterns or the amplifying effects of drought-stricken vegetation feedbacks.

But Randall Dole, deputy director of the agency’s Earth Systems Research Lab in Boulder, CO, and lead author of one of the studies is optimistic that helpful short-term forecasting is possible. He has been working on comparing what both the 2010 and 2003 mega-heatwaves have in common with other heat waves.

The key originator is an atmospheric condition known as a “blocking high” — a large stable pattern of subsiding air that diverts rain-bearing storms and allows nighttime and daytime temperatures to build up day after day. The hot, dry days lead to drought, the failure of vegetation and another key ingredient identified by a team at the European Centre for Mid-Range Weather Forecasting in their study of 2003 — a land surface feedback that amplifies the heating.

“There is a real consistency across all of these events,” Dole told Discovery News. “They have in common these atmospheric patterns that are favorable for both warm conditions and drought,” and they respond to drought with the amplifying land surface feedbacks as soils dry and plants die.

“I think there really is some hope here,” he said. “There is a real target in the one to two-week timescale that we ought to be focused on. So if something comes up this summer in Chicago or Des Moines, we want to be able to provide people with that lead time at least. And that can still be extremely useful and can save a lot of lives.”

IMAGE: NASA Earth Observatory/Jesse Allen