Event‐based classification for global study of river flood generating processes

Lina Stein,Francesca Pianosi,Ross Woods

doi:10.1002/hyp.13678

Abstract

AbstractBetter understanding of which processes generate floods in a catchment can improve flood frequency analysis and potentially climate change impacts assessment. However, current flood classification methods are either not transferable across locations or do not provide event‐based information. We therefore developed a location‐independent, event‐based flood classification methodology that is applicable in different climates and returns a classification of all flood events, including extreme ones. We use precipitation time series and very simply modelled soil moisture and snowmelt as inputs for a decision tree. A total of 113,635 events in 4155 catchments worldwide were classified into one of five hydro‐climatological flood generating processes: short rain, long rain, excess rainfall, snowmelt and a combination of rain and snow. The new classification was tested for its robustness and evaluated with available information; these two tests are often lacking in current flood classification approaches. According to the evaluation, the classification is mostly successful and indicates excess rainfall as the most common dominant process. However, the dominant process is not very informative in most catchments, as there is a high at‐site variability in flood generating processes. This is particularly relevant for the estimation of extreme floods which diverge from their usual flood generation pattern, especially in the United Kingdom, Northern France, Southeastern United States, and India.

Highlights

River flooding is a globally occurring natural hazard that takes many lives and causes extensive damage to property and infrastructure each year
A dominant flood generating process here is defined as the flood pro- routine parameters and input data uncertainty, as well as of the tree parameters and thresholds, is determents, this information is not as meaningful if flood generation varies mined using a regional sensitivity analysis method
We evaluate our results with the only global scale data available for comparison, the Dartmouth Flood Observatory (DFO) Global Active Archive of Large Flood Events (Brakenridge, 2018)

Summary

Introduction

River flooding is a globally occurring natural hazard that takes many lives and causes extensive damage to property and infrastructure each year. Blöschl et al (2017) showed that changes in the seasonal timing of extreme precipitation are not always the clearest explanatory factor for changes in the timing of floods, as in large areas of Europe flood occurrences are more influenced by timing of snowmelt or soil moisture maxima. This shows that rainfall alone is not the only driver of floods and river peak flow events can occur for multiple reasons. In addition to hydroclimatological processes (rainfall, snowmelt, rainfall excess on saturated ground, rain-on-snow), floods can be generated through blockages (e.g. ice jam, dam break) or tidal surges as well (Whitfield, 2012)

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Results

Conclusion