Changes in groundwater, rainfall, snowmelt and river water contribution to floods in the 1900-2100 period for a wetland catchment

Climate drives the hydrological response in a more complex way that would result from a water balance analysis. I this study such a complex, spatiotemporal behaviour of flooding a wetland catchment is presented over 200 years. The study site is the Biebrza River catchment located in north-eastern Poland. This medium size catchment, especially its floodplain, was preserved in a relatively unchanged state in the last centuries. The yearly floods in the wetland floodplain are driven by complex contribution water from precipitation, snowmelt, groundwater, and upstream river. The hydrological simulations were conducted using a fully-integrated groundwater-surface water hydrological model (HydroGeoSphere). The historical simulations were driven by the NOAA Twentieth Century Reanalysis, whereas the future climate simulation was driven by an ensemble of EURO-CORDEX downscaling datasets for rcp26, rcp45, and rcp85 pathways. The contribution of different water sources to the floods was analysed using the hydraulic mixing-cell method. The results show spatiotemporal trends and year-to-year variation of the flooding water composition, depth and extent in the analysed period. This complex response stresses the importance of taking into account full hydrologic system interactions, such as climate, timing and hydraulic feedbacks for climate change analysis.