CLIMATE-CHANGE IMPLICATIONS FOR STREAMFLOW AND STREAMWATER CHEMISTRY IN A MEDITERRANEAN CATCHMENT

MAGIC, a hydrochemical model of catchment acidification has been linke d to a model, PROFILE, which estimates catchment weathering rates, in an application to a small forested catchment in the Montseny mountains of Catalonia (northeast Spain), to assess the effects of climate chan ge on streamwater chemistry for a montane-Mediterranean region. Two sc enarios of climate change are considered: a 4 degrees C temperature in crease combined with 10% precipitation increase and a 4 degrees C temp erature increase combined with 10% precipitation decrease. The modelle d effect of a 10% precipitation increase on the water partition betwee n runoff and evapotranspiration is a slight dilution of the streamwate r chemistry, Correspondingly, the modelled effect of a 10% precipitati on decrease is a sharp concentration increase in streamwater chemistry . Weathering rates increase with increased temperature and increased p recipitation but are almost unaffected by increased temperature and de creased precipitation. Therefore, changes in streamwater concentration s, linked to the effect of weathering changes, appear only in the scen ario with a warmer and wetter climate. The approach has also been used to assess the effects of changing air mass patterns caused by climate change as an increase in alkaline-rich rains associated with Sahelo-S aharan dust may well result. This study indicates that the main chemic al changes following climate change will be associated with weathering rate changes rather than with changes in the atmospheric supply of ba se cations and alkalinity, The case for considering the effects of tem perature and moisture availability in climate change models of soil an d streamwater quality is shown to be overwhelming as rates of weatheri ng are strongly influenced by these factors.