Evaluation of regional very heavy precipitation events during the summer season using NARCCAP contemporary simulations

Regional climate models (RCMs) from the North American Regional Climate Change Assessment Program (NARCCAP) are compared with the two gridded precipitation datasets (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 vs. 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 so-called “widespread events”. Apart from the CRCM and EPC2 simulations, models and observations produce peaks in widespread events during 0300 UTC-0900 UTC, though the models typically produce slightly weaker intensities compared to observations. Widespread precipitation falls too frequently throughout the day, especially between 1500 UTC and 2100 UTC, compared to observations. Composite precipitation shows intermodel 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.This is the peer reviewed version of the following article: Kawazoe, Sho, and William J. Gutowski Jr. "Evaluation of regional very heavy precipitation events during the summer season using NARCCAP contemporary simulations." International Journal of Climatology 38 (2018): e832-e846, which has been published in final form at doi: 10.1002/joc.5412. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.</p

Extending medium-range predictability of extreme hydrological events in Europe

Widespread flooding occurred across northwest Europe during the winter of 2013/14, resulting in large socioeconomic damages. In the historical record, extreme hydrological events have been connected with intense water vapour transport. Here we show that water vapour transport has higher medium-range predictability compared with precipitation in the winter 2013/14 forecasts from the European Centre for Medium-Range Weather Forecasts. Applying the concept of potential predictability, the transport is found to extend the forecast horizon by 3 days in some European regions. Our results suggest that the breakdown in precipitation predictability is due to uncertainty in the horizontal mass convergence location, an essential mechanism for precipitation generation. Furthermore, the predictability increases with larger spatial averages. Given the strong association between precipitation and water vapour transport, especially for extreme events, we conclude that the higher transport predictability could be used as a model diagnostic to increase preparedness for extreme hydrological events