S1 Effects of 19th Century Records on Precipitation Trends for Select Midwestern Cities

Sunday, 10 January 2016
Hall E ( New Orleans Ernest N. Morial Convention Center)
Brendan C. Wallace, Midwestern Regional Climate Center, University of Illinois, Champaign, IL; and N. E. Westcott

Newly available data from the Climate Database Modernization Program (CDMP) Forts project has allowed the reconstruction of precipitation records extending back into the mid-19th century. An analysis of five major Midwestern United States cities: Minneapolis, Milwaukee, Chicago, Peoria, and St. Louis, indicates a tendency for larger amounts of both extreme and normal precipitation during the mid to late 19th century. Trends established in the pre-1895 values generally showed a tendency for precipitation totals to decrease during the latter portion of the 19th century. In addition, frequencies of heavy precipitation events greater than 1� were higher in the late 1800's than in the following decades of the early 20th century, and the precipitation from these heavy events was of a similar magnitude or greater than that found in the late 20th century.

Extensive quality control and the development of a metadata trail for each station were undertaken so as to ensure confidence in the quality of the data. An analysis of an �undercount bias� for each of the five stations showed that precipitation observers often did not record smaller precipitation totals (values ≤ 0.10�). Additionally, third party records were used to support the high precipitation totals early on in the precipitation observations, in particular for St. Louis, MO.

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