October 18, 2005
Tuesday AM

A new fine-scale supercomputer model of climate change calculates that the continental United States is in for longer heat waves, milder winters and exaggerated extremes of precipitation over the next 100 years.

The new model, run on supercomputers at Purdue University, breaks the 48 states down to blocks of about 10 square miles each, about twice the resolution of other models that have sought to project how a warming climate might impact weather patterns.

"One of the difficulties in preparing for climate change is getting the spatial nuances,'' said Noah Diffenbaugh, an assistant professor of earth and atmospheric sciences at Purdue and lead scientist for the study, published online Monday by the Proceedings of the National Academy of Sciences.

"Now we have projections for the whole lower 48 with the kind of spatial detail that matters for a power supplier, or a water utility, or a winemaker. And we're seeing that the spatial detail really matters for getting climate change projections correct, especially for extreme events,'' he added.

Along with the improved scale, the model is able to better take into account factors that have been fudged or ignored in other climate projections, such as the effect of snow reflecting solar energy back into space and high mountain ranges blocking weather fronts from traveling across them, the researchers said. It assumes that carbon dioxide and other greenhouse gases will more than double current levels over the next 100 years.

So much information was programmed into the cluster of computers at Purdue that it took five months to run the model, including a test run for the period 1961 through 1985 that fairly accurately matched what actually happened during those years.

The model anticipates that the continental United States will experience an overall warming trend, essentially canceling out the coldest two weeks of any given winter today and making the duration of the season generally shorter.

Among the specific projections:

The desert Southwest will have more heat waves of greater intensity combined with even less summer rain in Arizona, Colorado, New Mexico, Nevada and Utah.

The Gulf Coast will be hotter and wetter, but Diffenbaugh said the model projects "more dry spells punctuated by heavier rainfalls. We need to perform further analysis to understand how much of this is related to tropical cyclone activity."

In the Northeast, from east of Illinois and north from Kentucky, summers will be hotter and longer. "Imagine the weather during the hottest two weeks of the year. The area could experience temperatures in that range lasting for periods of up to two months by century's end."

The model also suggests that the coast of the Pacific Northwest and most of the country east of the Mississippi River will see more precipitation the rest of this century.

The findings are generally in agreement with models reported by scientists at NASA's Goddard Space Flight Center in Maryland last spring and last week by the National Center for Atmospheric Research (NCAR) in Boulder, Colo.

The NCAR model found that the greatest increases would be over land in the tropics, while NASA's model suggested more rain would fall over the oceans. But both models agreed that warming would bring heavier rain or snowfall in northwestern and northeastern North America, while exacerbating dry conditions in the Southwest.

Diffenbaugh stressed that the climate projections don't attempt to forecast any specific weather events, "but they do give us a good idea of what kind of weather to expect in the long run over a particular part of the country."

On the Net:

http://www.pnas.org

www.purdue.edu/climate

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