A study of national trend and variation in UK floods
International Journal of Climatology, 18 (2):
165--182 (1998)DOI: 10.1002/(SICI)1097-0088(199802)18:2<165::AID-JOC230>3.0.CO;2-#
Abstract
Trends in UK flood behaviour are examined using extensive peaks‒over‒threshold and annual maxima data from 890 gauging stations. The analysis focuses on changes that have occurred at the national scale; data were therefore pooled across all available sites. Two annual series are examined, representing flood size and frequency of flood occurrence. Results are presented for the 40‒year period 1941–1980, for the 50‒year period 1941–1990 (annual maxima only), and for some limited data for 1870–1995. Three main tests for trend (linear regression, normal scores regression and Spearman's correlation) were applied using (i) conventional theoretical significance levels, and (ii) a permutation approach. Test results were generally significant under the conventional approach but were not significant under the permutation approach. This difference occurs because some of the independence assumptions required for the conventional approach are not satisfied. There is a high year‒to‒year variation inherent in the data and, relative to this variation, any underlying trends are not significant. Regional and seasonal effects are considered but no significant trends emerge.Although no trends in national flood behaviour are seen, the year‒to‒year variations in UK floods appear to show some systematic behaviour (fluctuations) when smoothed using locally weighted regression. Further investigation suggests that these fluctuations are driven climatically; similar fluctuations are evident in UK annual rainfall values. The influence of climatic variation on the pattern of flood occurrences also means that, at the national scale, progressive changes in the UK flood regime, e.g. arising from land‒use change, are hidden. Over the period 1940 to 1980 smoothed curves suggest increased fluctuation, with emergence of some possible cyclic tendencies. However, in the context of the limited data going back to 1870, this increased fluctuation is not atypical. Overall, no evidence for climate change emerges for the periods for which data are currently available, although climate clearly has a marked effect on floods. The observed climate‒linked fluctuations indicate that inferences from short flood records may differ appreciably from those obtained from longer series. This could have potentially important implications for flood‒risk studies and trend detection. ©1998 Royal Meteorological Society.
Description
A study of national trend and variation in UK floods - Robson - 1998 - International Journal of Climatology - Wiley Online Library