final_program_abstracts[1]

11 IMSC Session Program
Changes in the annual largest daily rainfall totals
Friday - Poster Session 7
Mari Jones, C. G. Kilsby, H. J Fowler, S. Blenkinsop
School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon
Tyne, UK
Many studies have considered severe rainfall in terms of metrics expressing extremity
such as peaks over threshold, or quantiles of the observations, to maximise the data
available. However, the selection of a base period for these thresholds can have a
significant impact on the perceived trends. On the other hand, partial duration series
can limit the scope of any investigation by removing key information, and completely
ignore “drier” years.
A common method used in sea surge and, occasionally, wind storm analysis is that of
the “r-largest” events per year. We find this to be a statistically unbiased measure
which does not unduly reduce the available data, and which has not yet been explored
in great depth for extreme rainfall. The distribution of “r-largest” daily rainfall
accumulations in each year offers a unique representation of how extreme
precipitation patterns are changing, while also accounting for changes in “dry” years.
We establish the optimum number of events to include so that more regular rainfall
does not skew the data. After ranking the observations, we fit a multivariate EVD to
the top r events. From the event date, it is possible to approximate the seasonality and,
hence, likely controlling influences.
Abstracts 311