资源环境科技发展态势分析平台

Regional climate models (RCMs) from the North American Regional Climate Change Assessment Program (NARCCAP) are compared with the two gridded precipitation data sets [Climate Prediction Center (CPC) and the University of Washington (UW)] and the North American regional reanalysis (NARR) to examine if RCMs are able to reproduce very heavy precipitation under similar physical conditions seen in observations. The analysis focuses on contemporary climate (1982-1999) in an upper Mississippi region during the summer (June-July-August) months and utilizes output from NARCCAP RCMs forced with a reanalysis and atmosphere-ocean global climate models (AOGCMs).

The NARCCAP models generally reproduce the precipitation frequency versus intensity spectrum seen in observations up to around 25 mm day(-1), before producing overly strong precipitation at high intensities. CRCM simulations produce lower precipitation amounts than the rest of the models and observations past the 25 mm day(-1) threshold. Further analysis focuses on precipitation events exceeding the 99.5th percentile that occur simultaneously at several points in the region, yielding 'widespread events'. Apart from the CRCM and EPC2 simulations, models and observations produce peaks in widespread events during 0300-0900 UTC, although the models typically produce slightly weaker intensities compared to observations. Widespread precipitation falls too frequently throughout the day, especially between 1500 and 2100 UTC, compared to observations. Composite precipitation shows inter-model differences in magnitude and location of widespread events. Examination of additional fields shows that NARCCAP models produce credible representations of very heavy precipitation and their supporting environments when compared to the NARR.