Central European high-resolution gridded daily data sets (HYRAS): Mean temperature and relative humidity

High-resolution (5 x 5 km(2)) gridded daily data sets of surface air temperature (DWD/BfG-HYRAS-TAS) and relative humidity (DWD/BfG-HYRAS-HURS) are presented in this study. The data sets cover Germany and the bordering river catchments and last from 1951 to 2006. Their data bases consist of daily station observations from Austria, Belgium, Czech Republic, France, Germany, Luxembourg, the Netherlands and Switzerland. The interpolation of the measurement data to the regular grid is performed using a method based upon Optimal Interpolation. A first climatological analysis for Germany and Central European river catchments of first and second order is performed. For the Rhine river catchment a summer mean temperature of 16.1 degrees C and relative humidity of 74% are found. In contrast, the mean temperature of heat summer 2003 amounts to 19.9 degrees C with a related relative humidity of 65% in this river catchment. The extreme character of this summer is also remarkable in the presented climate indices, e.g., the increased amount of summer hot days. The first validations of both data sets reveal a bias within the range of the provided data precisions. In addition, an elevation dependency of error scores is identified for temperature. Error scores increase with an increasing station height because height differences between station and grid cell increases with height. A comparison of HYRAS-TAS to another gridded temperature data set reveals a good agreement with again fewer differences at lower altitudes. The presented DWD/BfG-HYRAS data sets have a high spatial and temporal resolution which is unique for Germany and the bordering river catchments so far. They have a high potential for detailed studies of smaller scale structures in Central Europe and are already used as input for hydrological impact modelling, as climatological reference and for bias correction of regional climate models within the German research project KLIWAS. HYRAS-TAS and HURS are part of the DWD/BfG-HYRAS data set which will finally include high-resolution gridded daily data of precipitation, temperature, relative humidity, solar radiation and wind speed.