A hard rain's gonna fallMonday, August 17, 2009
MIT News   (Browse all news)
Analysis shows climate change to yield more extreme rainfall — Heavier rainstorms lie in our future. That's the clear conclusion of a new MIT and Caltech study on the impact that global climate change will have on precipitation patterns. But the increase in extreme downpours is not uniformly spread around the world, the analysis shows.
Overall, previous studies have shown that average annual precipitation will increase in both the deep tropics and in temperate zones, but will decrease in the subtropics. However, it's important to know how the magnitude of extreme precipitation events will be affected, as these heavy downpours can lead to increased flooding and soil erosion. It is the magnitude of these extreme events that was the subject of this new research, which will appear online in the Proceedings of the National Academy of Sciences this week. The report was written by Paul O'Gorman, assistant professor in the Department of Earth, Atmospheric and Planetary Sciences at MIT, and Tapio Schneider, professor of environmental science and engineering at Caltech. (View article.)
Model simulations used in the study suggest that precipitation in extreme events will go up by about 5 to 6 percent for every one degree Celsius increase in temperature. Separate projections published earlier this year by MIT's Joint Program on the Science and Policy of Global Change indicate that without rapid and massive policy changes, there is a median probability of global surface warming of 5.2 degrees Celsius by 2100, with a 90 percent probability range of 3.5 to 7.4 degrees.
Specialists in the field called the new report by O'Gorman and Schneider a significant advance. Richard Allan, a senior research fellow at the Environmental Systems Science Centre at Reading University in Britain, says, "O'Gorman's analysis is an important step in understanding the physical basis for future increases in the most intense rainfall projected by climate models." He adds, however, that "more work is required in reconciling these simulations with observed changes in extreme rainfall events."
The reason the climate models are less consistent about what will happen to precipitation extremes in the tropics, O'Gorman explains, is that typical weather systems there fall below the size limitations of the models. While high and low pressure areas in temperate zones may span 1,000 kilometers, typical storm circulations in the tropics are too small for models to account for directly.