Construction of a 1961-1990 European climatology for climate change modelling and impact applications

A 1961-1990 mean monthly climatology for a 'greater European' region extending from 32 degrees W to 66 degrees E and from 25 degrees to 81 degrees N has been constructed at a resolution of 0.5 degrees latitude by 0.5 degrees longitude for a suite of nine surface climate variables: minimum, maximum, and mean air temperature; precipitation totals; sunshine hours; vapour pressure; wind speed; and (ground) frost day and rain day (>0.1 mm) frequencies. This climatology has been constructed from observed station data distributed across the region. Station frequencies range from 936 (wind speed) to 3078 (precipitation). Over 95 per cent of these data are based on observations between 1961 and 1990 and over 90 per cent were supplied by individual national meteorological agencies (NMAs) on specific request. For four variables, some standardization of the data had to be performed because different countries supplied data under different definitions. Thus cloud cover had to be converted to sunshine hours, relative humidity to vapour pressure, air frost days to ground frost days and rain days > 1 mm to rain days >0.1 mm. The interpolation of the station data to the grid used elevation as one of the predictor variables and thus enabled three climate surfaces to be produced for each variable, reflecting the minimum, mean, and maximum elevation within each 0.5 degrees by 0.5 degrees cell. Subsets of stations were used for the interpolation of each variable, the selection being based on optimizing the spatial distribution, source priority and length of record. The accuracy of the various interpolations was assessed using validation sets of independent station data (i.e. those not used in the interpolation). Estimated mean absolute errors (MAE) ranged from under 4 per cent for vapour pressure to about 10 per cent for precipitation and up to 20 per cent for wind speed. The accuracy of the interpolated surfaces for minimum and maximum temperature was between 0.5 degrees C and 0.8 degrees C. We believe these results constitute the first climatology that has been constructed for this extensive European region at such a fine spatial resolution (0.5 degrees by 0.5 degrees) from relatively dense station networks, for three different elevation surfaces and for a wide range of surface climate variables, all expressed with respect to a standard 30-year period. The climatology is already being used by researchers for applications in the areas of ecosystem modelling, climate change impact assessment and climate model validation, and is available from the authors.