1. 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
A Watershed Year: Anatomy of the Iowa Floods of 2008
Lessons Learned – Preparing for the Future
Des Moines, Iowa 
9 March 2010

2. Observed Trends in Iowa Precipitation

3. State-Wide Average Data

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

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

6. State-Wide Average Data

8. Cedar Rapids Data
28.0”
32% increase
37.0”

9. Cedar Rapids Data
51% increase
11.8”
7.8”

10. Cedar Rapids Data
34% increase
20.2”
26.8”

11. “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.

12. Cedar Rapids Data
57% increase
6.6 days
4.2 days

13. 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

15. 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,

16. Projected Future Trends in Iowa Precipitation

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

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

19. 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
The temperature scale at left is in degrees Centigrade, and
temperature anomalies are calculated relative to a reference period
averaged from 1890 to 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

20. 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.

21. 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.

22. 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.

23. 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.

24. Relationship of Streamflow to Precipitation in Current and Future Climates

25. 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

26. 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

27. For More Information
North American Regional Climate Change Assessment Program:
For current activities on the ISU campus, regionally and nationally relating to climate change see the Climate Science Initiative website:
Contact me directly: