UK seasonal river flow variability in near-natural catchments, regional outflows and long hydrometric records

This article presents an assessment of changes and variability in seasonal river flows in the UK, using three complementary datasets spanning different periods and spatial scales: 1) 95 small, near-natural catchments, 1969 - 2008, 2) regional outflows for large areas of the UK, 1961 - 2008 and 3) eight major catchments with records from pre-1940 to 2008. The most notable patterns to emerge are an increase in winter and autumn river flows in some regions, which appear to be robust, spatially and temporally. Spring and summer trends were generally much weaker, spatially very variable, and in both these seasons the direction of trends changes over the course of the longer records. Overall, the results suggest stability in seasonal mean flows – with limited evidence for changes which are of significance for water management – but reveal much complexity in the temporal and regional patterns, which warrant detailed investigation in future. This work provides a baseline of seasonal river flow variability against which emerging changes and model projections can be assessed.