An assessment of runoff trends in natural catchments in the Celtic regions of North West Europe.

This study presents results of trend tests applied to annual and seasonal runoff time series from a network of largely undisturbed catchments across the Celtic Region of northwest Europe (the British Isles and Brittany), with a view to discerning natural variability from artificial influences on flow regimes. Strong evidence of runoff increases over the last 40-years was found for Scotland and Ireland, and there were some significant increases in Wales, western England and Brittany, although the regional signals are less compelling in these areas. The findings have some parallels with climate change scenarios, although there were also strong associations with the North Atlantic Oscillation Index over this timescale; the influence of the NAO is likely to account for the spatial variability in the significance of trends which was observed over the region. The study provides a baseline against which to assess historical variability and future runoff trends in the Celtic region.