August 5, 2012
An Environment Colorado Research & Policy Center report finds that extreme rain and snowstorms are occurring 25% more frequently in Colorado and the mountain region since 1948.
When It Rains, It Pours: Global Warming and the Increase in Extreme Precipitation from 1948 to 2011 examines trends in the frequency and precipitation amounts produced by extreme rain and snowstorms across the contiguous U.S. from 1948 to 2011.
More storms; more precipitation
Based on an analysis of state data from the National Climatic Data Center, the ECRPC report found that heavy rain and snowstorms now occur in Colorado every 9.6 months on average, instead of once every 12 months on average. Additionally, the largest annual storms in Colorado now produce 8% more precipitation, on average, than they did 65 years ago.
Using data from 3,700 weather stations and a methodology developed the NCDC and the Illinois State Water Survey, the report identifies storms with the greatest 24-hour precipitation totals at each station, and when those storms occurred. The report also examines trends in the amount of precipitation produced by the largest annual storm at each location.
According to ECRPC, scientists have concluded that the rise in the frequency and severity of heavy rainstorms and snowstorms is linked to global warming. Warming increases evaporation and enables the atmosphere to hold more water, resulting in extreme rainstorms and heavy snowstorms. Yet evaporation and soil dryness mean the water produced by these storms is not often available for human use.
“Changes in precipitation and water availability are likely the biggest pressure point on society as the climate changes,” said Dr. Kevin E. Trenberth, distinguished senior scientist at the National Center for Atmospheric Research.
Climate change & drought
“Increases in extremes are already observed and projected to get worse,” said Trenberth. “As well as more intense rains (and snows), the risk of severe drought also goes up. We have experienced the latter in the United States this year while floods have occurred in Japan, Europe and China. Management of water is already a major challenge and adding climate change makes it more so.”
As global warming intensifies, said ECRPC, longer periods with relatively little precipitation will tend to mark the periods between heavy rainstorms. As a result, droughts are likely to become more frequent and severe in some regions of the US. In the summer of 2012, more than half of the lower U.S. is experiencing prolonged drought, aggravated by the fact that the last six months were the hottest January-June period on record.
ECRPC cited analysis that the U.S. must reduce its total global warming emissions by at least 35% below 2005 levels by 2020 and by at least 85% by 2050 to prevent the most devastating consequences of global warming. The group highlighted two proposals — carbon pollution and fuel efficiency standards for cars and light trucks through model year 2025, and carbon pollution standards for new power plants — as critical steps toward meeting pollution reduction targets.
For more information and to view the report, visit the Environment Colorado Research and Policy Center website.