Impact of local climate change on groundwater resources and surface water availability in headwater catchments

About 90% of rivers and streams are originating in headwater catchments. Headwater catchments are more susceptible to climate change and sensitive to drought conditions. Extreme weather events (such as extended drought periods) are affecting water availability in headwater catchments which are important source areas for downstream river networks. Climate change is predicted to affect water availability for surface water bodies and groundwater alike. Future projections indicate that increasing temperature will affect the water balance with higher evapotranspiration rates. Headwater streams are often dependent on groundwater input specifically during baseflow conditions in summer/late summer. It is therefore important to investigate the potential impact of climate change on the interaction between surface water and groundwater in headwater catchments. As part of this study, we investigated the impact of local climate change on small scale surface/groundwater interactions for a small headwater catchment (Grosse Ohe) located in the Bavarian Forest (Germany). We used a the fully integrated hydrological model HydroGeoSphere (HGS) to represent surface groundwater interactions for the catchment. Simulations include data from regional climate change models (RCM) as input to represent future scenarios up to the year 2100. Results showed that increasing temperature causes higher evapotranspiration rates which significantly affects the water availability in headwater streams. Simulations indicate that climate change is responsible for more frequent drought periods during summer where groundwater inflow into the streams declines by up to 35% compared to the past (2002 to 2018). We also evaluated local exchange fluxes between groundwater and stream for the entire catchment. Here, simulations indicate that formerly gaining stream sections in future are more frequently turn into losing sections especially during extended baseflow conditions in summer. This may have severe consequences for the ecosystem as stream sections in future are prone to lose their entire water to the subsurface.