On the value of hourly precipitation extremes in regional climate model simulations

Hourly precipitation extremes in the Netherlands in eight transient (1951-2099) and five ERA40 driven (1961-2000) regional climate model (RCM) simulations were analyzed. Generalized extreme value (GEV) distributions were fitted to the annual maximum amounts. Large differences were found between the estimated GEV parameters for the RCM simulations and those for an 11-year (1998-2008) high-quality radar data set. There were also large differences between the GEV parameters for different RCM simulations. The influence of the boundary conditions (ERA40 or a global climate model simulation for the present climate) on the extreme value distributions was in most cases small. A similar analysis for the daily precipitation extremes revealed much smaller differences between RCM simulations and a much better agreement with the results for the radar data. The increase in large quantiles of the daily maxima at the end of the 21st century in the transient RCM simulations was much smaller than that in the quantiles of the hourly maxima. For the latter, large differences were found between the changes from different RCM simulations, partly resulting from an increase in the GEV shape parameter in a number of RCM simulations. This increase in the shape parameter also largely explains the differences between the changes in large quantiles of the hourly and daily precipitation extremes. (C) 2010 Elsevier B.V. All rights reserved.