Extreme precipitation events are predicted to go up 6% with each degree Celsius, according to a computer model. The prediction of increased precipitation with global warming has been around for a while. For the United States, precipitation since 1970 has averaged about 5% more than in the previous 70 years (Karl et al., 1996), and cold season precipitation has increased by almost 10% during the last century. An increase in snowfall was also observed in the 1960s and 1970s in China. Precipitation hitting the US from hurricanes has increased by 7% over the twentieth century.
http://www.ucsusa.org/global_warming/science_and_impacts/impacts/early-warning-signs-of-global-3.htmlThe computer models suggest an increase in extreme weather events, also.
http://en.wikipedia.org/wiki/Effects_of_global_warmingScienceDaily (Sep. 27, 2009) — 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.
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 frequency and magnitude of extreme precipitation events will be affected, as these heavy downpours can lead to increased flooding and soil erosion.
Model simulations used in the study suggest that precipitation in extreme events will go up by about 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
However, contrary to what might be expected, extremes events do not increase at the same rate as the moisture capacity of the atmosphere. The extremes do go up, but not by as much as the total water vapor, he says. That is because water condenses out as rising air cools, but the rate of cooling for the rising air is less in a warmer climate, and this moderates the increase in precipitation, he says.
Heavier Rainstorms Ahead Due To Global Climate Change, Study Predicts