Plants' Wilting Point Linked to Brutal Heat Waves

Copyright © 2009 National Public Radio®. For personal, noncommercial use only. See Terms of Use. For other uses, prior permission required.

ROBERT SIEGEL, host:

Many people who study climate change predicted that brutal heat waves could become more common as the Earth gets warmer. But until recently it wasn't clear why some heat waves turn into killers and some don't. Now a new study offers an explanation. Apparently, the answer is in the dirt beneath your feet.

NPR's John Nielsen reports.

JOHN NIELSEN: In 2003, a major heat wave fried most of Europe. Alpine glaciers melted. Rivers like the Danube trickled. In the Vatican, Pope John Paul II urged the world to pray for rain. In France, where many thousands died, critics like Eve Condasue(ph) said the government should've been better prepared.

Mr. EVE CONDASUE (French citizen): (Through translator) They say it's the family's fault, it's the neighbor's fault or the fault of the local city council. I'm really wondering what we pay ministers for. It's scandalous.

NIELSEN: The new study published in the current issue of Nature could help governments be better prepared next time. It's by a team of scientists led by Sonia Senabaratna(ph), a climate research with the Institute for Climate Science in Zurich, Switzerland. She spent the summer of 2003 inside a boiling hot room full of computers trying to figure out what turns a merely awful heat wave into a catastrophic killer.

She was testing a theory and held that water in the soil helped to buffer most heat waves by providing plants with moisture they released into the hot air. But what happens when a hot spell hits after a long drought, she wondered.

Ms. SONIA SENABARATNA (Institute for Climate Science): What happens is that at some point if soil moisture content is very low you reach a critical threshold.

NIELSEN: Technically this threshold is called the wilting point, the point at which there's no water left for plants to suck out of the soil. The study says that's also the point at which a typical heat wave starts to morph into something much more dangerous.

Senabaratna says she reached that conclusion after breaking down several recent European heat waves. She found that the roughest heat waves were linked to the driest soil conditions.

Now it happens that these findings dovetail neatly with soil and heat wave studies being done in the United States. These studies suggest that heat waves will become more severe in the future, but not everywhere. William Schlesinger, a climate expert at Duke University, says coastal areas won't be hurt as badly.

Mr. WILLIAM SCHLESINGER (Duke University): The models of future climate suggest that the central parts of continents will become dryer in a warmer climate. For North America that might include a fairly large swath of the Great Plains. In this paper there's a suggestion of Eastern Europe, western parts of Russia and the Ukraine becoming dryer.

NIELSEN: Schlesinger says the bad news here is that these are some of the most productive farming centers in the world. But Sonia Senabaratna says there is at least one piece of good news in these findings. In the future as soil moisture levels are measured more systematically, she says it could become easier for governments to know when the risk of a killer heat wave is high.

John Nielsen, NPR News, Washington.

Copyright ©2009 National Public Radio®. All rights reserved. No quotes from the materials contained herein may be used in any media without attribution to National Public Radio. This transcript is provided for personal, noncommercial use only, pursuant to our Terms of Use. Any other use requires NPR's prior permission. Visit our permissions page for further information.

NPR transcripts are created on a rush deadline by a contractor for NPR, and accuracy and availability may vary. This text may not be in its final form and may be updated or revised in the future. Please be aware that the authoritative record of NPR's programming is the audio.