Extreme daily precipitation in Western Europe with climate change at appropriate spatial scales

Extreme daily precipitation for the current and changed climate at appropriate spatial scales is assessed. This is done in the context of the impact of climate change on flooding in the river Meuse in Western Europe. The objective is achieved by determining and comparing extreme precipitation from stations, reanalysis projects, global climate models and regional climate models. An extreme value reduction methodology based on extreme precipitation correlation structure and surface area is used to deal with the transformation between different spatial scales. It appeared that return values are simulated quite well by the regional climate models and CSIRO9, but are underestimated by the reanalyses and overestimated by CGCM1 and HadCM3. The models simulated an average increase in extreme precipitation with climate change of about 18%, which is in the same range as the average model error and intermodel differences. The appropriate spatial scale for representing extreme precipitation was estimated at 20 km, when the bias permitted in the estimation of extreme precipitation is set at 10%. Downscaling modelled extreme precipitation to this appropriate scale results in considerable differences between reanalysis and GCM scale and appropriate scale return values. It is therefore obvious that return values at these appropriate scales should be used instead of at their original scale