Streamflow trends in western Britain

Abstract

Concerns about recent river flow changes are increasing, given their importance for water management, flooding, drought mitigation, and geomorphological and ecological processes. For the first time, this paper develops a full picture of recent streamflow trends over the period 1962-2001 for western Britain across the entire flow spectrum, at annual and seasonal resolutions, for 56 gauging stations and three study periods. Annual and seasonal trends are calculated and mapped using the non-parametric Mann-Kendall test with bootstrap resampling. Several significant, mainly positive, trends are observed at high and low flows, while mean flows are relatively stable. A marked east-west gradient of streamflow trend emerges, with more significant and positive trends in the mountainous west, particularly for autumn and winter high flows. Positive annual low flow trends are found across western Wales, largely driven by increasing summer base flow. Many trends are consistent with previously observed rainfall and North Atlantic Oscillation (NAO) changes.