The impact of land use scenarios on the water balance in the Thaya river basin

The Thaya river basin is one of the key river basins in the southern part of the Czech Republic. Due to extensive river regulations and partial drainage of the basin area, it belongs to river basins sensitive to climate change impacts. This is supported by significant negative runoff trends over the past 40 years. The main aim of this contribution is to analyze impacts of the hypothetical land use changes on the hydrological processes of the upper Thaya basin. In this study, we used a hydrological Mike SHE model. The physically based and spatially distributed model Mike SHE was calibrated and validated using measured river discharge data in the three hydrological profiles for the period 1991–2020. Selected hypothetical adaptation land use scenarios including the vegetation cover changes were compared to the reference scenario (represents the current land use of the basin) to analyze the impacts of the simulated land use changes on the hydrological processes in the basin. Except the field management changes, the land use scenarios encompassed extreme vegetation changes, where the entire basin in the model was changed to (1) grassland, (2) mixed deciduous-coniferous forest, (3) deciduous forest, or (4) cropland. These extreme land use scenarios were analyzed for several CMIP6 downscaled climate models and different RCP emissions scenarios up to the end of the first half of the 21st century. The results showed that the evapotranspiration is the dominant water loss component for all simulated land use scenarios in the basin. The highest evapotranspiration was modeled for the mixed deciduous-coniferous forest, while the lowest was for the grassland and cropland scenarios. The Mike SHE model also simulated that the total runoff was lowest for both forest scenarios. Results of the study showed the sensitivity of the river basin on the climate change impacts, where a slight increase of the evapotranspiration value in the basin has a significant effect on the total runoff from the basin. This study was conducted within the evaluating and designing nature-based adaptation measures to climate change in the Thaya river basin.