Risk-based flood protection planning under climate change and modeling uncertainty: a pre-alpine case study

Beatrice Dittes,Olga Špačková,Markus Disse,Wolfgang Rieger,Maria Kaiser,Daniel Straub

doi:10.5194/nhess-18-1327-2018

Beatrice Dittes, Olga Špačková + Show 4 more

Open Access

https://doi.org/10.5194/nhess-18-1327-2018

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Abstract

Abstract. Planning authorities are faced with a range of questions when planning flood protection measures: is the existing protection adequate for current and future demands or should it be extended? How will flood patterns change in the future? How should the uncertainty pertaining to this influence the planning decision, e.g., for delaying planning or including a safety margin? Is it sufficient to follow a protection criterion (e.g., to protect from the 100-year flood) or should the planning be conducted in a risk-based way? How important is it for flood protection planning to accurately estimate flood frequency (changes), costs and damage? These are questions that we address for a medium-sized pre-alpine catchment in southern Germany, using a sequential Bayesian decision making framework that quantitatively addresses the full spectrum of uncertainty. We evaluate different flood protection systems considered by local agencies in a test study catchment. Despite large uncertainties in damage, cost and climate, the recommendation is robust for the most conservative approach. This demonstrates the feasibility of making robust decisions under large uncertainty. Furthermore, by comparison to a previous study, it highlights the benefits of risk-based planning over the planning of flood protection to a prescribed return period.

Highlights

Technical flood protection measures have long lifetimes of, on average, 80 years (Bund/Länder-Arbeitsgemeinschaft Wasser, 2005)
Planning authorities are faced with a range of questions when planning flood protection measures: is the existing protection adequate for current and future demands or should it be extended? How will flood patterns change in the future? How should the uncertainty pertaining to this influence the planning decision, e.g., for delaying planning or including a safety margin? Is it sufficient to follow a protection criterion or should the planning be conducted in a risk-based way? How important is it for flood protection planning to accurately estimate flood frequency, costs and damage? These are questions that we address for a medium-sized pre-alpine catchment in southern Germany, using a sequential Bayesian decision making framework that quantitatively addresses the full spectrum of uncertainty
We interpolate linearly between damage for individual discharges as given in Fig. 9, using the resulting damage function in the optimization framework to arrive at the results given

Summary

Introduction

Technical flood protection measures have long lifetimes of, on average, 80 years (Bund/Länder-Arbeitsgemeinschaft Wasser, 2005). The uncertainty over such a long planning horizon is large, both in terms of climatic and socioeconomic development. It is not trivial for planning authorities to take decisions on flood protection planning that are economical while not leading to excessive losses or high adjustment costs. It is important to consider costs – in construction, adjustment and flood damage – over the entire measure life time. The planning of flood protection infrastructure is performed through a risk-based approach. Considering that the annual maximum discharge Q is the main driver for flood damage, the annual flood risk in year t, rt , is defined as follows (e.g., Merz et al, 2010):

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