Spatial and temporal variability of UK river flow regimes

This paper investigates the spatial distribution and temporal stability of annual flow regimes within the UK, using 25-year records for 35 gauging stations. A multivariate, statistical classification of regime "shape" and "magnitude" is used: (a) to regionalize long-term average regimes and (b) to establish inter-annual variability (stability) in regimes at stations and within "regions". Regionalization yields four "shape" classes with different timing of major flow peaks and three "magnitude" classes. Stability analysis identifies six "shape" and four "magnitude" classes. These results suggest regime "shape" is controlled by the seasonal distribution and nature of hydroclimatic inputs. Although regime "magnitude" decreases along a west-east precipitation gradient at the UK scale, inter-annual variations in "magnitude" at a station may be linked to large-scale atmospheric circulation patterns, particularly during the autumn recharge season. Both regime "Shape" and "magnitude" are influenced by geology; basins associated with major aquifers exhibit greater stability in regime "shape". However, strong synoptic climatological forcing may cause a single regime type to dominate across the UK.