Modelling of future groundwater recharge in the metropolitian area of Hamburg (Germany) under changed climate conditions

According to current climate projections, the metropolitan area of Hamburg, Germany is at risk for changes in the hydrological budget. These changes are expected to have direct impacts on the long-term water availability for e.g. agricultural productivity and drinking water supply. In the south-eastern part of the Metropolitan area for instance agricultural production without restrictions is only possible by means of field irrigation, especially during dry summers. It can be foreseen that the future management of water resources has to consider appropriate adaptation measures in order to feed the water demand of different sectors. The main target of a research project carried out by the authors in the framework of the BMBF research priority “KLIMZUG-NORD” is the modelling of the possible impact of climate change on groundwater availability and irrigation needs in the metropolitan area of Hamburg. For this purpose, the water balance model GROWA (Wendland et al., 2003) has been further developed to the mGROWA model (Herrmann et al., 2012) which is able to simulate runoff components (e.g. groundwater recharge) in daily time-steps and with high spatial resolution (100 m grid). The mGROWA model will be briefly introduced and its application to the metropolitan area will be presented. At first the simulation performance for the reference period (1961-2005) will be presented, e.g. with regard to the simulated temporal variable water content in the root zone (and thus to the irrigation demand) and groundwater recharge. This is followed by the presentation of the results of several model runs in which a climate data ensemble (REMO, WETTREG2010) is used as model input for the period 1980-2100. Finally, the expected changes in the hydrological budget until 2100 and the resultant impacts on groundwater resources management will be discussed. References: Wendland, F., Kunkel, R., Tetzlaff, B., Dörhöfer, G. (2003): GIS-based determination of the mean long-term groundwater recharge in Lower Saxony. Environmental Geology 45, 273-278. Herrmann, F., Engel, N., Chen, S., Heidt, L., Kunkel, R., Müller, U. & Wendland, F. (2012, in preparation): Das Modell mGROWA zur Simulation des Landschaftswasserhaushaltes in hoher zeitlicher Auflösung. Schriften des Forschungszentrums Jülich Reihe Umwelt/ Environment. Research Centre Jülich; Jülich