Simulated impact of past and possible future land use changes on the hydrological response of the Northern German lowland 'Hunte' catchment

Land use is a key factor controlling the hydrological behaviour of catchments. Changing land use therefore can have an important influence on the local hydrological cycle. Validated and process-based hydrological models are suitable tools to quantify the impact of a change in land use on the hydrological processes. In this study, the physically based catchment model WaSiM-ETH (Water Balance Simulation Model) was applied to a mesoscale lowland catchment in northern Germany (Hunte river, 2141 km(2) at gauge Oldenburg). Model calibration and validation showed that WaSiM-ETH well represented the discharge of the main Hunte river while the discharge dynamics of a few lowland tributaries whose catchments are characterised by peaty soils and intense artificial drainage could not be represented. The purpose of this study was twofold; on the one hand to analyse the sensitivity of WaSiM-ETH to changes in land use observed in the decade 1990-2000, and on the other hand to quantify the impact of land use change projected for the future in terms of land use scenarios available to the public. The results showed that WaSiM-ETH is hardly sensitive to the slight changes observed in the last decade of the 20th century. By contrast, water flows simulated by WaSiM-ETH are clearly impacted by agricultural land use scenarios which were developed based on IPCC scenarios. However, the results also show that it is not sufficient to focus on agricultural land use, only. The proposed reduction of agricultural land leaves open the final land cover after land use change, e.g., forest or urban areas. This study demonstrated that WaSiM-ETH was more sensitive to the choice of the final land cover than to the difference in the scenarios (e.g., A1F1 versus B1). Therefore, we recommend to precisely define change in agricultural land use as well as the final land cover in order to estimate the realistic impact of land use change on hydrological behaviour. (C) 2009 Elsevier B.V. All rights reserved.