Evaluating climate change impacts on the hydrology of Kamp catchment, Austria, under different shared social pathways (SSPs)

Climate change can severely affect water fluxes at the land surface and thereby water availability as well as floods and droughts leading to increased risks for man-environment systems. Understanding the impacts of climate change on future water resources at a catchment scale is essential for strategic planning and efficient integrated water resources management. In the frame of the DISTENDER project (EU Horizon-ID 101056836), climate change impacts upon several catchments in Europe are analyzed. A key goal of DISTENDER is to develop robust strategies for climate change adaptation. For the simulation of climate change impacts on water resources, the Soil and Water Assessment Tool (SWAT+) was selected for its accessibility, robustness, and transferability. Here we address the issue of effects of different climate models vs. shared socioeconomic pathways (SSPs) by driving SWAT with results of three models (CanESM5, EC-EARTH3, MPI-ESM1-2-HR) run of the updated Coupled Model Intercomparison Project Phase 6 (CMIP6) with four SSPs (SSPs 1-2.6, 2-4.5, 3-7.0, 5-8.5), respectively. The Kamp River in Lower Austria was selected as an example catchment because it is the longest river in the Waldviertel region, which has significant ecological, societal, and economic importance. The SWAT+ model was calibrated and validated at different locations in the catchment. Future climate change projections for the period 2021 to 2050 were obtained from CMIP6 and were statistically downscaled. Annual 3-day high runoff was used as a proxy for the extreme high runoff characteristics. Trends and variations of the water balance components were compared. All climate models show an increase in average annual precipitation ranging from 5 % (MPI-ESM1-2-HR) to 17 % (CanESM5). In all climate models and SSPs, the 3-day high runoff at Stiefern gauge (near the catchment outlet) for 10, 50, and 100-year return periods is projected to increase. CanESM5 and EC-EARTH3 show the highest (54 %) and the lowest (13 %) increase in the 3-day high runoff for 10, and 100-year return periods respectively, variations across the SSPs range from 12 % (SSP1-2.6) to 77 % (SSP 5-8.5) for 100-year return periods. Changes in the average annual evapotranspiration across the different models range from 12 % to 18 %, and variations across the SSPs range from 14 % to 16 %. For all models, the average annual soil moisture in the catchment decreases significantly (5 % to 18 %), across SSPs the decrease ranges from 9 % to 13 %. Our results indicate that the effects of choosing different models to reflect the changes in the runoff and average annual water balance components exceed the effects of different SSPs. Thus, decision-makers and planners should select a model according to their planning goal (i.e. use a model with extreme change to reflect the maximum potential risk). This research is intended to develop adaptation and mitigation strategies to reduce risks and vulnerabilities and to contribute to effective management of water resources in the catchment within the framework of the DISTENDER project. Keywords: Climate change, CIMP6 Climate Model, SWAT+ model, Kamp catchment, Austria