Trends in Iowa Precipitation: Observed and Projected Future Trends 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 50011 gstakle@iastate.edu A Watershed Year: Anatomy of the Iowa Floods of 2008 Lessons Learned – Preparing for the Future Des Moines, Iowa  9 March 2010

Observed Trends in Iowa Precipitation

State-Wide Average Data

State-Wide Average Data 37.5” 31.5” 19% increase

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

State-Wide Average Data

Cedar Rapids Data 28.0” 32% increase 37.0”

Cedar Rapids Data 51% increase 11.8” 7.8”

Cedar Rapids Data 34% increase 20.2” 26.8”

“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 101.6 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.

Cedar Rapids Data 57% increase 6.6 days 4.2 days

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

Great Flood of 1993 in the US Midwest: A New “Great Lake” Historical Data indicate this should happen about once every 500 years Lakshmi, V., and K. Schaaf, 2001: Analysis of the 1993 Midwestern flood using satellite and ground data. IEEE Trans. Geosci & Remote Sens., 39, 1736-1743.

Projected Future Trends in Iowa Precipitation

“The future isn’t what it used to be” Yogi Berra

Global Carbon Emissions (Gt) Actual emissions are exceeding worst case scenarios projected in 1990

Source: Jerry Meehl, National Center for Atmospheric Research From Jerry Meehl This slide shows the time evolution of globally averaged surface air temperature from multiple ensemble simulations of 20th century climate from the NCAR Parallel Climate Model (PCM) compared to observations. The simulations start in the late 19th century, and continue to the year 2000. The temperature scale at left is in degrees Centigrade, and temperature anomalies are calculated relative to a reference period averaged from 1890 to 1919. The black line shows the observed data, or the actual, recorded globally averaged surface air temperatures from the past century. The blue and red lines are the average of four simulations each from the computer model. The pink and light blue shaded areas depict the range of the four simulations for each experiment, giving an idea of the uncertainty of a given realization of 20th century climate from the climate model. The blue line shows the average from the four member ensemble of the simulated time evolution of globally average surface air temperature when only "natural" influences (solar variability and volcanic eruptions) are included in the model. Therefore, the blue line represents what the model says global average temperatures would have been if there had been no human influences. The red line shows the average of the four member ensemble experiment when natural forcings AND anthropogenic influences (greenhouse gases including carbon dioxide, sulfate aerosols from air pollution, and ozone changes) are included in the model. Note that this model can reproduce the actual, observed data very well only if the combined effects of natural and anthropogenic factors are included. The conclusion that can be drawn is that naturally occuring influences on climate contributed to most of the warming that occurred before WWII, but that the large observed temperature increases since the 1970s can only be simulated in the model if anthropogenic factors are included. This confirms the conclusion of the IPCC Third Assessment Report that most of the warming we have observed in the latter part of the 20th century has been due to human influences. Source: Jerry Meehl, National Center for Atmospheric Research

Karl, T. R. , J. M. Melillo, and T. C. Peterson, (eds 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.

Karl, T. R. , J. M. Melillo, and T. C. Peterson, (eds 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.

Low confidence 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.

Trend of increase in occurrence of heavy precipitation over the 20th C is consistent with increasing GHG concentrations. Frequency of intense precipitation events is likely to increase in the future. 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.

Relationship of Streamflow to Precipitation in Current and Future Climates

SWAT (RegCM2): 21 % increase in precip -> 50% increase in streamflow Relationship of Streamflow to Precipitation in Current and Future Climates DrainMod (RegCM2): 24 % increase in precip -> 35% increase in tile drainage DrainMod (HIRHAM): 32 % increase in precip -> 80% increase in tile drainage

Will These Iowa Precipitation Trends Continue? Caution: These are my speculations!! In the short-term (next 5-10 years) precipitation characteristics will be dominated by natural variability from base conditions of the past 30 years (not long-term averages) If we continue to have high spring and summer rainfall and soil moisture, we likely will continue to have higher chances of flooding In the longer term (>50 years), hot summers, milder winters, and higher variability of precipitation will become more dominant Failure to limit global carbon emissions will accelerate trends toward more extremes of precipitation compared to the 20th Century

For More Information North American Regional Climate Change Assessment Program: http://www.narccap.ucar.edu/ For current activities on the ISU campus, regionally and nationally relating to climate change see the Climate Science Initiative website: http://climate.agron.iastate.edu/ Contact me directly: gstakle@iastate.edu