Effects of spatial data resolution on the calculation of regional water balances

Regional simulation demands the reduction of the amount of data and computer time required. In this study the effect of data availability on the annual water balance is investigated. It was found, in a given drainage basin, that the areal mean evapotranspiration and groundwater recharge can be calculated using soil maps at different resolutions. In this way an upscaling of these hydrological processes is possible, in principle without a bias in the simulation results. But in the drainage basin investigated distinct spatial patterns of the differences in hydrological behaviour were observed which correspond to the geological origin. The runoff production therefore showed a strong dependence on the natural variability of soil hydraulic properties and the concept of effective parameters fails in this case; Assuming a lognormal probability distribution of the decisive parameter "saturated hydraulic conductivity" however, and choosing a suitable sampling scheme (Latin Hypercube method) this heterogeneity can be taken into account in modelling the hydrological behaviour.