Climate Change effects on the River Discharge in Bulgaria

The impact of future climate change under IPCC scenarios RCP4.5 and RCP8.5 on hydrological regimes in plain catchments up to 650 m high and in mountainous areas of Bulgaria is discussed. A hydrological simulation models (TUWmodel) were calibrated on recorded data and ‘forced’ in the selected scenarios with precipitation and air temperature data from ALADIN 5.2, a local version of the French global atmospheric model ARPEGE, downscaled to a grid of 12 km. Simulations for the future periods 2013-2042, 2021-2050 and 2071-2100 are compared to the flows in the reference period 1976-2005.

Results indicate increased seasonality of flows, with noticeably drier summers and increase of river discharge in winter. In most of the cases the analysis of extreme events suggests significant increases in the frequency of both high‐ and low‐flow events. The change in the extreme runoff with a large repetition period required for the design of flood protection structures and systems has been investigated in regions with different mechanisms for flood generation. With the push of RCP4.5 or RCP8.5 scenarios the significant increase in flood peaks is observed in most of the river basins. There is a general trend of decreasing runoff with a 95% probability of exceedance.