Climatic Variations in Extreme Precipitation in the Midwest

In the Midwest, signi cant interannual to decadal variations in precipitation and stream ow have been observed over the latter part of this century. Yet in studies of precipitation frequency, engineers and hydrologists assume that natural climate variability does not a ect the probability distribution of extreme precipitation. A regional approach is used to test this assumption for extreme precipitation in the Midwest for precipitation durations ranging from 1-hour to 3-days. Homogeneous regions for precipitation frequency analysis are delineated and regional time series of precipitation quantiles are estimated. Variations in the regional quantile series for precipitation return periods of 2to 20-years are compared with those expected for a stationary random process. The sensitivity of the statistical analysis to the delineation of homogeneous regions and to the handling of missing hourly precipitation data are examined. The implications of the results for the use of regional precipitation frequency estimates in ood design are