Date and Time: Wednesday, 6 February⋅1:00 – 2:00pm
Location: Slingo LT, JJT Building, Whiteknights Campus, University of Reading
Title: Trends in UK Peak Flow Data: When did they start?
Speaker: Adam Griffin (Centre for Ecology and Hydrology)
There is currently a great deal of interest in the potential effects of climate and environmental change on the magnitude and frequency of extreme floods. For example, repeated extreme floods experienced in north-west England over the last few years have caused concern about whether such events are evidence of changes in flood-producing mechanisms. Classical approaches to flood frequency analysis rely on the assumption of stationarity, i.e. that there is no trend in the peak flow data. However, the occurrence of the most extreme events (larger than any other on record) can have a marked effect on return period estimates, which in turn introduces uncertainty when considering the design lifetime of flood risk management measures. This paper describes the application of non-stationary flood frequency analysis to annual maxima time series in the UK, and how characteristics of the most extreme events change over time.Following on from work on low and high flows by Harrigan et al. 2017, trends in extreme flood distributions in the United Kingdom have been investigated. The UKBN2 is a near-rural collection of UK catchments with long records (more than 40 years) which makes it possible to investigate possible hydrological and meteorological trends without having to account for the influence of river management and land use change. Fitting time-dependent location, scale and shape parameters of the Generalised Logistic distribution enabled us to see the changes in flood frequency curve characteristics over time. Additionally, fitting time-independent distributions over moving and increasing time-windows allows us to identify when particular events have a marked influence on parameter estimates and hence flood frequency curves. Spatial patterns in these parameter changes across the UK are evaluated together with changes through time. Examples of changes in the 30-, 50- and 100-year floods are presented for stations in the Benchmark Network.
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