Catchments on the cusp? Structural and functional change in northern ecohydrology

There is already compelling evidence that climate change in northern temperate, boreal and sub-arctic catchments is having a major effect on hydrological processes (McClelland et al., 2006; Rennermalm et al., 2010). The Commentary considers the cascade of implications of changes in the annual water balance and seasonal streamflow distribution that can be anticipated for water quality and in-stream ecology in northern regions. Critical uncertainties, urgent research needs and sensitivities in the water balance are identified, highlighting that many of these catchments are ‘on the cusp’ of major change. In particular, uncertainties over the key role of natural or managed changes in catchment vegetation in mediating the impacts on the water quantity, quality and ecology of river systems will be emphasized. Addressing this research gap will be critical in providing support for adaptive land management aimed at protecting water resources and sustaining ecosystem services. The focus for the discussion are nine catchments (see Carey et al., 2010 for details) included in the North-Watch (www.abdn.ac.uk/northwatch) project, an international network of experimental catchments for comparative hydrological study, which span a range of hydroclimatic conditions in the mid-latitude to highlatitude region (e.g. Carey et al., 2010). The availability of hydrochemical and ecological data at most of these catchments facilitated synthesis in hypothesizing the integrated projections of climatic warming. Figure 1 shows the projected climate changes between present and the mid-21st century for these nine sites. Although predicted changes in precipitation totals are small at most sites, temperature increases will be marked as General Circulation Model (GCMs) project some of the most dramatic global temperature increases for this region (Intergovernmental Panel on Climate Change, IPCC, 2007; Kundzewicz et al., 2007).