A GIS-supported method for detecting the hydrological mosaic and the role of man as a hydrological factor

Abstract

A Geographical Information System (GIS)-supported method was developed for predicting the spatial distribution of soil wetness as an indicator to determine the probability of an area to act as a groundwater recharge or discharge area. The method was based on overlays of maps with the distribution of hydrological response-determining factors. An application was made for the Svarta river basin (south-central Sweden). Changes in the soil-wetness mosaic due to human activities were also analyzed. Since the 1870s drainage and forestry had, according to the analysis, decreased by 5% the parts of the basin that act as discharge areas during wet spells. In the agriculturally dominated sub-basins, the alterations were larger. Forty percent of the open land had been artificially drained. The main shift of soil wetness index classes was caused by an alteration of areas that earlier fluctuated between groundwater discharge and recharge into typical recharge areas. For the plains, the shift from discharge areas to recharge areas was also significant. A conceptual water partitioning model was used to assess the spatial distribution of water flows (evaporation and recharge), as a response to climatic inputs, for areas with different physiographic and vegetative characteristics. The present water flow pattern was compared with the response mosaic of the 1870s. The increased maximum daily recharge peaks during autumn constitute the only significant change in the hydrological response for the studied area as a whole. The consequences that the desiccation of the landscape have on chemical and biological processes were discussed.