9 February 2011

A deadly heat wave is finally hindcasted

Posted by mjvinas

This image shows the differences in day time land surface temperatures collected in the two years by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite. (Credit: NASA)

In 2003, an extreme heat wave in Europe brought record temperatures that lasted throughout the summer and killed tens of thousands of people. In many regions, the heat wave led to massive forest fires and devastated agriculture. One study from the World Glacier Monitoring Service showed that glaciers in the Alps lost an average thickness of 3 meters during the heat.

Since then, a number of meteorological studies tried unsuccessfully to re-forecast – or forecast in hindsight – that summer’s extreme weather, but none were able to create a totally accurate model of the event. Scientists ultimately hope to be able to predict such scorchers before they hit.

A research team now says that it has succeeded in re-forecasting the range of conditions across Europe during the 2003 heat wave. The team includes scientists from the European Centre for Mid-Range Weather Forecasting, or ECMWF, and the University of Oxford.

In a paper to be published by Geophysical Research Letters, the authors report that their model represents the first accurate simulation of not only the unusual heat, but also the observed rainfall and atmospheric circulation patterns. The study by ECMWF’s Antje Weisheimer and his colleagues finds that unusually hot and dry soil was the main driver of the heat wave.

Other models of the heat wave had assumed that unusual sea surface warmth played the most significant role in the heat wave, but the new research indicates that early-summer hot and dry soils were much more important. By using an advanced surface model developed by the European forecasting center, Weisheimer and his collaborators were able to accurately re-forecast the catastrophic weather.

“The new model version that we have tested … includes a better representation of the physical processes at the land surface, for example improved soil properties,” says Weisheimer. The improved soil model, called H-TESSEL, was used to reconstruct the hot and dry conditions that persisted from May throughout the summer. Re-forecast attempts using a previous model showed no sign of a heat wave whatsoever.

This improvement in understanding of the European heat wave might help forecasters better predict similar future events. However, Weisheimer cautions that advances in modeling don’t necessarily translate into a real-world warning of a heat wave.

“ECMWF’s forecast model is one of the most advanced” for forecasts looking several months ahead, says Weisheimer. “Whether the model is indeed able to forecast any future heat wave in a similar realistic manner as 2003 remains to be seen.”

Eric Betz, contributing science writer.

Antje Weisheimer1, Francisco J. Doblas-Reyes, Thomas Jung and T.N. Palmer (2011). On the predictability of the extreme summer 2003 over Europe Geophysical Research Letters