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Extreme Precipitation Events in the United States
Reference
Kunkel, K.E., Easterling, D.R, Redmond, K. and Hubbard, K.  2003.  Temporal variations of extreme precipitation events in the United States: 1895-2000.  Geophysical Research Letters 30: 10.1029/2003GL018052.

Background
The Intergovernmental Panel on Climate Change (Cusbasch et al., 2001) has said "it is likely that there has been a widespread increase in heavy and extreme precipitation events in regions where total precipitation has increased (e.g., the mid- and high-latitudes of the Northern Hemisphere," noting it is also highly likely that increases in heavy precipitation extremes will occur during the 21st century (Houghton et al., 2001), thus giving climate alarmists reason to claim that every extreme precipitation event that occurs nowadays is evidence of the reality of CO2-induced global warming.

What was done
Kunkel et al. assessed the validity of these claims with a new data set produced by the Climate Database Modernization Project (2001), which consists of daily precipitation observations from the conterminous United States for the period 1895-2000.  This data base covers a much longer span of years than that investigated by the studies upon which the IPCC based its conclusions, and it includes many more meteorological monitoring stations as well.

What was learned
The scientists' analysis revealed that "heavy precipitation frequencies were relatively high during the late 19th/early 20th Centuries, decreasing to a minimum in the 1920s and 30s, followed by a general increase into the 1990s."  More specifically, they note that "for 1-day duration events, frequencies during 1895-1905 are comparable in magnitude to frequencies in the 1980s and 1990s," while "for 5- and 10-day duration events, frequencies during 1895-1905 are only slightly smaller than late 20th Century values."

What it means
First of all, Kunkel et al. note that "inspection of time series of extremes based on just the last 50-70 years lead[s] to quite different qualitative conclusions than those based on the 107-year record" of the 1895-2000 period, which suggests that the IPCC was perhaps a little hasty in drawing its apparently errant conclusions from a data base that was clearly inadequate for the purpose to which it was applied.  In addition, they note that since enhanced greenhouse gas forcing of the climate system was very small in the early years of the 1895-2000 record, the elevated extreme precipitation frequencies of that time "were most likely a consequence of naturally forced variability," further suggesting, in their words, "the possibility that natural variability could be an important contributor to the recent increases."

We agree with all their conclusions and applaud them and the members of the Climate Database Modernization Project for searching out as much data as possible in order to derive as robust conclusions as possible from their analyses.

References
Climate Database Modernization Project.  2001.  Annual Report, available from the National Climatic Data Center, Asheville, NC, USA.

Cusbasch, U., Meehl, G.A., Boer, G.J., Stouffer, R.J., Dix, M., Noda, A., Senior, C.A., Raper, S. and Yap, K.S.  2001.  Projections of future climatic change.  In: Houghton, J.T., Ding, Y., Griggs, D.J., Noguer, M., van der Linden, P.J., Dai, X., Maskell, K. and Johnson, C.A. (Eds.).  Climate Change 2001: The Scientific Basis.  Contributions of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK.

Houghton, J.T., Ding, Y., Griggs, D.J., Noguer, M., van der Linden, P.J., Dai, X., Maskell, K. and Johnson, C.A. (Eds.).  2001.  Climate Change 2001: The Scientific Basis.  Contributions of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK.


Reviewed 8 October 2003