Quantifying Uncertainty in the Modelling Process; Future Extreme Flood Event Projections Across the UK

Cameron Ellis,Gordon Aitken,Annie Visser-Quinn,Lindsay Beevers

doi:10.3390/geosciences11010033

Cameron Ellis, Gordon Aitken + Show 2 more

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https://doi.org/10.3390/geosciences11010033

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Journal: Geosciences	Publication Date: Jan 8, 2021
Citations: 5	License type: CC BY 4.0

Affiliation: Heriot-Watt University

Abstract

With evidence suggesting that climate change is resulting in changes within the hydrologic cycle, the ability to robustly model hydroclimatic response is critical. This paper assesses how extreme runoff—1:2- and 1:30-year return period (RP) events—may change at a regional level across the UK by the 2080s (2069–2098). Capturing uncertainty in the hydroclimatic modelling chain, flow projections were extracted from the EDgE (End-to-end Demonstrator for improved decision-making in the water sector in Europe) multi-model ensemble: five Coupled Model Intercomparison Project (CMIP5) General Circulation Models and four hydrological models forced under emissions scenarios Representative Concentration Pathway (RCP) 2.6 and RCP 8.5 (5 × 4 × 2 chains). Uncertainty in extreme value parameterisation was captured through consideration of two methods: generalised extreme value (GEV) and generalised logistic (GL). The method was applied across 192 catchments and aggregated to eight regions. The results suggest that, by the 2080s, many regions could experience large increases in extreme runoff, with a maximum mean change signal of +34% exhibited in East Scotland (1:2-year RP). Combined with increasing urbanisation, these estimates paint a concerning picture for the future UK flood landscape. Model chain uncertainty was found to increase by the 2080s, though extreme value (EV) parameter uncertainty becomes dominant at the 1:30-year RP (exceeding 60% in some regions), highlighting the importance of capturing both the associated EV parameter and ensemble uncertainty.

Highlights

The overarching aim of this paper is to investigate how extreme runoff may change on a regional level across the UK by the 2080s, as well as the uncertainty associated with these projections
The following analysis was applied at the catchment and regional levels: (1) the mean change signal, a quantification of the change in extreme runoff estimates; (2) relative standard deviation (RSD), which captures the spread of model chain outcomes and structural uncertainty; and (3) the probability distribution uncertainty (PDU), the standardised difference between the upper and lower 95% confidence limits across the modelling chains, capturing the extreme value (EV) parameter uncertainty
Collet et al [20] investigated the projected change in future flood events across Scotland and the uncertainty associated with these projections

Summary

Introduction

Floods are a common hydrological hazard that pose widespread threat to lives and infrastructure [1,2]. According to UN estimates, in the period of 1995–2015, 2.3 billion people were affected (either in terms of health or socioeconomics) by floods globally, resulting in 157,000 fatalities and a total cost of USD 662 billion in economic damage [3]. In the UK, millions of people are affected by flooding every year, with annual flood damage costs estimated to be in the region of GBP 1.1 billion [4]. The UK government spent GBP 808.2 million on flood risk management in 2018/2019, a GBP 144.9 million increase in expenditure in just over ten years (2005/2006, [5])

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