Trends in Iowa Precipitation: Observed and Projected Future Trends Christopher J. Anderson, PhD Scientist, Assistant Director Climate Science Initiative Iowa State University Tracy L. Rowlandson Ph.D. Candidate, Agricultural Meteorology Department of Agronomy, Iowa State University Eugene S. Takle Director, Climate Science Initiative Professor of Atmospheric Science Department of Geological and Atmospheric Sciences Professor of Agricultural Meteorology Department of Agronomy Iowa State University Ames, Iowa Christopher J. Anderson, PhD Scientist, Assistant Director Climate Science Initiative Iowa State University Tracy L. Rowlandson Ph.D. Candidate, Agricultural Meteorology Department of Agronomy, Iowa State University Eugene S. Takle Director, Climate Science Initiative Professor of Atmospheric Science Department of Geological and Atmospheric Sciences Professor of Agricultural Meteorology Department of Agronomy Iowa State University Ames, Iowa A Watershed Year: Anatomy of the Iowa Floods of 2008 Lessons Learned – Preparing for the Future Cedar Rapids, Iowa 21 June 2010

The Two Questions Most Frequently asked about Changes in Rainfall  What role might have been played by climate change in recent heavy rainfall events?  Will similar heavy rainfall events happen in the the future?  What role might have been played by climate change in recent heavy rainfall events?  Will similar heavy rainfall events happen in the the future?

“One of the clearest trends in the United States observational record is an increasing frequency and intensity of heavy precipitation events… Over the last century there was a 50% increase in the frequency of days with precipitation over mm (four inches) in the upper midwestern U.S.; this trend is statistically significant “ Karl, T. R., J. M. Melillo, and T. C. Peterson, (eds.), 2009: Global Climate Change Impacts in the United States. Cambridge University Press, 2009, 196pp.

State-Wide Average Data

31.5” 37.5” 19% increase

State-Wide Average Data Totals above 40” 8 years 2 years

Cedar Rapids Data 4.2 days 57% increase 6.6 days

Cedar Rapids Data 4.2 days 57% increase 6.6 days 2 11 Years having more than 8 days

What role might have climate change played in recent heavy rainfall events?  More water vapor is in the air over the Midwest.  Warmer surface temperature in Gulf of Mexico and Caribbean; this is a direct link to climate change.  Increase in agricultural production and irrigation  Pacific sea surface temperature pattern is conducive to a wet period in the recent 15 years.  More storm systems steered into rather than north of the Midwest  Likely a continuation of historical climate variability.  The importance of soil conditions: wet soils promote more rainfall, more rainfall keeps soil conditions wet.  The relative importance of these factors and their connection to climate change are matters of research and debate.  More water vapor is in the air over the Midwest.  Warmer surface temperature in Gulf of Mexico and Caribbean; this is a direct link to climate change.  Increase in agricultural production and irrigation  Pacific sea surface temperature pattern is conducive to a wet period in the recent 15 years.  More storm systems steered into rather than north of the Midwest  Likely a continuation of historical climate variability.  The importance of soil conditions: wet soils promote more rainfall, more rainfall keeps soil conditions wet.  The relative importance of these factors and their connection to climate change are matters of research and debate.

Will similar heavy rainfall events happen in the future?  In the next 5-10 years precipitation will be more like the past 30 years than the 50 to 100 years before that.  Between 10 and 20 years from now, days with heavy rainfall similar to the past 30 years will occur intermittently during periods of drought.  Beyond 30 years from now, greater highs and lows of rainfall will emerge.  Seasonal rainfall will likely increase in spring and decrease in summer  Maximum daily rainfall likely to continue to increase  In the next 5-10 years precipitation will be more like the past 30 years than the 50 to 100 years before that.  Between 10 and 20 years from now, days with heavy rainfall similar to the past 30 years will occur intermittently during periods of drought.  Beyond 30 years from now, greater highs and lows of rainfall will emerge.  Seasonal rainfall will likely increase in spring and decrease in summer  Maximum daily rainfall likely to continue to increase

For More Information  For current activities on the ISU campus, regionally and nationally relating to climate change see the Climate Science Initiative website:  Contact:  For current activities on the ISU campus, regionally and nationally relating to climate change see the Climate Science Initiative website:  Contact: