Detection and spatial modelling of trends in UK rainfall frequency

An analysis is presented of trends in the magnitude and frequency of extreme rainfall in the UK, for durations of 1–16 days. A spatial extreme value model is fitted to improve the detection of any signal of non-stationarity, test the explanatory power of climatic covariates and explore the spatial variability of trends. While most individual raingauges show no significant trend, there is evidence of non-stationarity across the dataset as a whole. Trends in maximum rainfalls are more common for longer durations and in the winter season, particularly in the north. Trends are generally towards higher annual maxima and more frequent peaks over a threshold. The spatial model represents both spatial and temporal variations in rainfall frequency, as well as how these vary with rainfall duration. It shows that trends in annual maximum rainfall can be represented by including the North Atlantic Oscillation index as a covariate.