Long-term Mean Precipitation Distribution 1981 - 2010
The REGNIE grids of multi-annual precipitation for Germany covering the period from 1981 to 2010 were used as the statistical base (retrieved on September 29, 2020). The DWD provides these as part of a freely available data set via the Climate Data Center (CDC).
The REGNIE data is embedded in a geographic grid, with a latitudinal spatial resolution of 60 geographical seconds and a longitudinal spatial resolution of 30 geographical seconds. In the ETRS 1989 UTM zone 33N projection, this corresponds roughly to a 1 km x 1 km grid.
Precipitation data is available for multiple reference periods (1961-1990, 1971-2000, 1981-2010) and reflects the 30-year mean amount of precipitation (in millimetres) for each calendar month, the four seasons and the entire year per period. In order to be able to balance the amount of precipitation for the water years 1981-2010 (see below), the monthly REGNIE grids for November and December of the years 1980 and 2010 were also taken into account.
The DWD has ensured that the precipitation data used in the REGNIE method is complete and consistent and has corrected the data where necessary. The REGNIE grids do not correct for systematic precipitation losses due to wetting, evaporation and wind effects, however. Measurement errors are influenced by many factors, including the station type, installation site, precipitation pattern and precipitation type. For conventional precipitation gauges (Hellmann) across the Nordostdeutsches Tiefland (Northeast German Plain), the precipitation measurement error in the annual mean ranges between 8.6 and 16.6 %, depending on wind exposure (cf. Richter 1995, only in German).
The REGNIE regionalisation method is essentially based on the interpolation of anomalies in relation to long-term means. For this purpose, background fields are determined for precipitation distributions. Based on these, the amount of precipitation is then calculated. Background fields are calculated by multiple linear regression taking into account geographical location, altitude, slope and direction of slope that may influence the amount of precipitation and its distribution. As a next step, the measured station precipitation and the background fields are interpolated to calculate regionalised precipitation.
The REGNIE method is described in detail in Rauthe et. al. 2013 (only in German). See DWD 2017 (only in German) for a brief description focussing on data provision and use. See DWD 2018 for a description of the data set.