|Title:||Regional analysis of extreme rainfalls in Denmark|
|Abstract||The aim of the project is to establish a regional model for estimation of extreme rainfall properties in Denmark for specific application in urban drainage modelling. The data material consists of measurements from a country-wide system of high resolution rain gauges that has been operated since 1979, at present corresponding to a total of more than 800 station years of data. Extreme rainfall characteristics have been modelled using the partial duration series (PDS) approach. Assessment of homogeneity of the regional PDS, determination of a regional distribution, and investigation of the potential of describing any regional variability from climatic and physiographic characteristics have been analysed using various statistical test procedures based on L-moments and regression analysis based on generalized least squares estimation. The analysis reveals that the frequency of occurrence of extreme events is significantly correlated with the mean annual precipitation. For the mean of the exceedances in the PDS a significant metropolitan effect is observed, the extreme events in the Copenhagen area being significantly larger than in the rest of the country. With respect to higher order moments, which determine the shape of the extreme value distribution, the region can, in general, be considered homogeneous, supporting the use of a common regional distribution. The findings have a significant impact on the use of rainfall data in urban drainage design, and new guidelines are presently being prepared.
The study is part of the research project "Data treatment and stochastic modelling of rainfall and runoff in urban areas" funded by Det Kommunale Momsfond and the Danish Water Pollution Control Committee. The project is carried out in cooperation with Department of Environmental Science and Engineering, DTU.|