Will catchment characteristics moderate the projected effects of climate change on flow regimes in the Scottish Highlands?

Regional climate models were used with the UKCP09 weather generator to downscale outputs from the HadCM3 General Circulation Model, to project climate change by 2050 in the Scottish Highlands. The resulting hydroclimatic data were used to drive a tracer‐aided hydrological model to assess likely changes in flow regimes in three experimental catchments. These are located along a hydroclimatic transect from the wet, mild western Highlands (Strontian), through the colder, more continental central Highlands (Allt a' Mharcaidh), to the drier eastern Highlands (Girnock). At all sites, temperatures are projected to increase by around 2 °C, with associated increases in potential evapotranspiration. Precipitation is expected to increase by around 10–15% at Strontian but remains slightly changed at the Allt a' Mharcaidh and Girnock. However, the seasonal distribution of precipitation is projected to change, increasing in winter and decreasing in summer. Cautious interpretation of model outputs indicates that flows are likely to change accordingly at all sites, though the characteristics of each catchment result in some subtle differences. At Strontian, marked increases in winter high flows are expected, at the Allt a' Mharcaidh, reduction in winter snowfall and reduced snowpack will increase winter high flows and moderate the influence of spring melts. In the Girnock, decreasing summer low flows are the most notable element of change. These subtle differences in response to climatic drivers are consistent with the distinct storage characteristics of the catchments which in turn reflect their landscape evolution histories. Copyright © 2012 John Wiley & Sons, Ltd.