Observations and Regional Climate Model Simulations of Heavy Precipitation Events: A Comparision

Abnormal wetness for monthly and seasonal time periods is often caused in large part by a few days of excessive precipitation. Conversely, abnormally dry periods are usually characterized by an absence of such events, while the frequency of light events often changes only slightly. Assessments of the impacts of climate change on the Midwest are typically based on the output of global and regional climate models. To assess certain impacts, it is essential that such models accurately simulate the frequency and magnitude of the rare heavy events. The reanalysis products of the National Centers for Environmental Prediction (NCEP) and the European Center for Medium-Range Weather Forecasting (ECMWF) provide one basis for assessing models’ ability to simulate such events. Since these models are constrained by observations, they probably represent something close to an upper bound on the potential accuracy of climate simulations that are not constrained by observations. Diagnostic study of NCEP and ECNWF reanalysis data for recent decades is being performed. Specifically, the historical record has been categorized into wet, normal, and dry seasons. The frequency and magnitude of heavy precipitation episodes in the observational data sets for the Midwest are being compared with the reanalysis products. The results of this assessment will be described.