Modification of climate–river flow associations by basin properties

Given heightened concerns about climate and human impacts upon hydrology, there is a need to quantify temporal and spatial variability in water availability, and to establish climate-flow associations to predict future water stress. In the UK, most previous climate-river flow research: (1) used single sites or a network of basins with restricted geographical coverage and/or sparse density; (2) included river flow records impacted by anthropogenic influences; (3) generally recognised the importance of basin properties but did not advance beyond broad basin characterisation. This paper addresses these research gaps and aims to improve understanding of seasonal hydroclimatological associations across the UK by: (1) characterising spatial patterns in winter, spring, summer and autumn flows; (2) identifying regions for which atmospheric circulation (AC) and regional climate (RC) drivers exert strongest control on seasonal flows; and (3) identifying basin properties that have a significant influence on seasonal flows. 104 gauged basins covering mainland Great Britain and having near-natural flow records were used to derive four seasonal flow indices for 1975-2005. For each calendar season, cluster analysis was performed on these indices to group hydrologically similar basins. For each resultant class, climate-flow associations were assessed as well as the identification of influential basin physical properties. RC variables were found to have stronger association with seasonal flows than AC with the best RC predictors varying with season. Only winter and summer showed significant AC-flow correlations. Composition of seasonal flow classes reflected not only climatic input but also the physical nature of the basins. A given basin property may have influence for one season, but not for another; and many properties have only limited influence on modifying climate inputs. For both winter and summer seasons, it may be concluded generally that the higher elevation and more impermeable a basin, the stronger the RC-flow association. For AC-flow associations, regions of significant winter correlations match regions of stronger RC-flow association; summer correlations show an eastern shift. This paper illustrates the important (but variable) role of basin properties in modifying climate signals in river flow and the need to consider both sets of controls in evaluating hydrological sensitivity to climate change. (C) 2010 Elsevier B.V. All rights reserved.