Euro-limpacs Deliverables



Dynamically−downscaled data from two Atmosphere−Ocean General Circulation Models (AOGCMs), ECHAM4 from the Max−Planck Institute (MPI), Germany, and HadAm3H from the Hadley Centre (HAD), UK, driven with two scenarios of greenhouse gas emissions (IS92a and A2, respectively) were used to make climate change projections and then to drive four effect models linked to assess the effects on hydrology and nitrogen (N) concentrations and fluxes in the 685 km2 Bjerkreim river basin and its coastal fjord, southwestern Norway. The four effect models were the hydrological model HBV, the water quality models MAGIC, INCA−N, and the NIVA FJORD model. The downscaled climate scenarios project a general temperature increase in the study region, of approximately 1oC by 2030−2049 (MPI IS92a) and approximately 3oC by 2071−2100 (HAD A2). Both scenarios imply increased winter precipitation, whereas the projections of summer and autumn precipitation are quite different, with the MPI scenario projecting a slight increase and the HAD scenario a significant decrease. As a response to increased winter temperature the HBV model simulates a dramatic reduction of snow accumulation in the upper parts of the catchment, which in turn lead to higher runoff during winter and lower runoff during snowmelt in the spring. With the HAD scenario runoff in summer and early autumn is substantially reduced, as a result of reduced precipitation, increased temperatures and thereby increased evapotranspiration. The water quality models MAGIC and INCA−N project no major changes in nitrate (NO3−) concentrations and fluxes within the MPI scenario, but a significant increase in concentrations and a 40−50% increase in fluxes in the HAD scenario. As a consequence the acidification of the river could increase, thus offsetting ongoing recovery from acidification due to reductions in acid deposition. Additionally, the increased N loading may stimulate growth of N−limited benthic algae and macrophytes along the river channels and lead to undesirable eutrophication effects in the estuarine area. Simulations made by the FJORD model and the HAD scenario indicate that primary production in the estuary might increase up to 15−20%, based on the climate−induced changes in river flow and nitrate concentrations alone.

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