Simulating flood event sets using extremal principal components
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Hazard event sets, which correspond to a collection of synthetic flood events, are an important tool for practitioners to analyse and manage future flood risks. In this paper, we address the issue of generating hazard event sets for northern England and southern Scotland, a region which has been particularly affected by flooding over the past years. We start by analysing extreme river flow across 45 gauges in the region using recently introduced ideas from extreme value theory. This results in a set of extremal principal components, with the first components describing the large-scale structure of the observed flood events, and we find interesting connections to the region's topography and climate. We then introduce a framework to approximate the distribution of the extremal principal components which is dimension reducing in that it distinctly handles the large-scale and local extremal behavior. Synthetic flood events are subsequently generated efficiently by sampling from the fitted distribution. Our approach for generating hazard event sets can be easily implemented by practitioners and our results indicate good agreement between the observed and simulated extreme river flow dynamics.
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