Trends in Iowa Precipitation: Observed and Projected Future Trends

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Trends in Iowa PrecipitationObserved 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_at_iastate.edu

A Watershed Year Anatomy of the Iowa Floods of
2008 Lessons Learned Preparing for the
Future Des Moines, Iowa  9 March 2010
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Observed Trends in Iowa Precipitation
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State-Wide Average Data
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State-Wide Average Data
37.5
31.5
19 increase
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State-Wide Average Data
Totals above 40
8 years
2 years
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State-Wide Average Data
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Cedar Rapids Data
28.0
37.0
32 increase
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Cedar Rapids Data
51 increase
11.8
7.8
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Cedar Rapids Data
34 increase
20.2
26.8
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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.
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Cedar Rapids Data
57 increase
6.6 days
4.2 days
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Cedar Rapids Data
Years having more than 8 days
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2
57 increase
6.6 days
4.2 days
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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.
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Projected Future Trends in Iowa Precipitation
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The future isnt what it used to be Yogi Berra
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Global Carbon Emissions (Gt)
Actual emissions are exceeding worst case
scenarios projected in 1990
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Source Jerry Meehl, National Center for
Atmospheric Research
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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.
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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.
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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.
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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.
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Relationship of Streamflow to Precipitation in
Current and Future Climates
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SWAT (RegCM2) 21 increase in precip -gt 50
increase in streamflow
Relationship of Streamflow to Precipitation in
Current and Future Climates
DrainMod (RegCM2) 24 increase in precip -gt
35 increase in tile drainage
DrainMod (HIRHAM) 32 increase in precip -gt
80 increase in tile drainage
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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 (gt50 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

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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_at_iastate.edu