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Abstract

During the last years, numerous groundwater logging stations in Brandenburg indicate a considerable decrease of groundwater table depth. Variations of percolation due to changes of the driving meteorological conditions (decrease in precipitation and/or increase of temperature) are supposed to be the reason for this decrease.
In order to study the complex system behaviour including meteorological, landuse and soil type conditions, simulation runs using a high resolution precipitation-runoff model were carried out for the State of Brandenburg (30.000 km²). Water balance calculations with a daily time step were performed for the period 1961-1998 on the basis of 57.836 spatial units, which result from the GIS-based combination of various digital maps. For the simulation runs, these units were spatially aggregated into 1.599 hydrotopes and 15 hydrotope classes.
Comprehensive analyses of various time series as well as spatially distributed results reveal tendencies influencing the regional water cycle in general and percolation in particular. Percolation was statistically analysed for different periods and temporal aggregations (annual, winter, summer, quarterly and monthly values). The results of the spatially distributed trend analyses indicate considerable changes of water balance components in Brandenburg in the period 1961-1998. Though only the increase of mean daily temperature by about 1 °C turns out to be statistically significant, 75% of the total area of Brandenburg show a decrease in percolation. For almost 5% of the area this decrease is statistically significant.
Differentiating the observed trends with respect to the 15 hydrotope classes used for the simulation runs shows that only areas characterized by a shallow groundwater table contribute to this decrease. The basic reasons for the percolation trend are decreasing precipitation sums and increasing mean daily temperatures. The period 1991-1998 characterized by many hot summers contributes considerably to this behaviour.
The application of the high resolution GIS-based modelling approach shows that this concept represents an effective way to study trends in various water balance components. Thus, it is a basic element in integrated studies heading for an improved water management and a more sustainable water use, as e.g. stimulated by the European Water Directive.