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Climate: Ready for more intense rainstorms?

Western Colorado expected to see increase in heavy rainfall events

The map at right shows predicted changes in the annual number of days of extreme rainfall (defined as rainfall totals in excess of the historic 98th percentile) across the United States by 2041-2070 as compared to 1971-2000 if greenhouse gases continue to increase at a high rate (A2 scenario).

This map shows predicted changes in the annual number of days of extreme rainfall (defined as rainfall totals in excess of the historic 98th percentile) across the United States by 2041-2070 as compared to 1971-2000 if greenhouse gases continue to increase at a high rate.

Staff Report

FRISCO — There may not be an observed trend of more frequent, intense rainstorms in Colorado yet, but that could change in coming decades, according to a national climate assessment.

The 2009 federal climate study shows that heavy downpours have increased in frequency and intensity during the last 50 years and models predict that downpours will intensify even more as greenhouse gas emissions and the planet’s temperature continue to rise. By mid-century, some places could experience two or more additional days per year on which the rainfall totals exceed the heaviest rains historically experienced in the area.

Climate models project increasing days of extreme rainfall in the Northwest, Midwest, and parts of the Northeast, including some populated coastal areas that are already challenged by inundation and sea level rise.

Several major watersheds are predicted to have more days of extreme rainfall by the middle of the century, including the Pacific Northwest, the Ohio River Basin, the Great Lakes, and parts of the Great River and Missouri River Basin. Meanwhile, the Southwest and some other areas frequented by drought are expected to see little difference in the number of extreme rainfall days.

The main targets so far have been the Northeast and Midwest where the amount of rain falling in the heaviest downpours has increased approximately 20 percent on average in the past century.

These trends are widely thought to be associated with the fact that warmer air temperatures fuel more evaporation, which leads to a wetter atmosphere. Scientists have measured a significant increase in specific humidity (the volume of water vapor) over the Earth’s surface, which is consistent with the long-term warming trend in our planet’s average surface temperature.

 

Related Links
USGCRP report Weather and Climate Extremes in Changing Climate, Chapter 3

Global Climate Change Impacts in the United States (2009) (pdf)

Coupled Model Intercomparison Project

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