Abstract
Abstract. Recent studies have shown evidence of increasing and decreasing trends for average floods and flood quantiles across Europe. Studies attributing observed changes in flood peaks to their drivers have mostly focused on the average flood behaviour, without distinguishing small and large floods. This paper proposes a new framework for attributing flood changes to potential drivers, as a function of return period (T), in a regional context. We assume flood peaks to follow a non-stationary regional Gumbel distribution, where the median flood and the 100-year growth factor are used as parameters. They are allowed to vary in time and between catchments as a function of the drivers quantified by covariates. The elasticities of floods with respect to the drivers and the contributions of the drivers to flood changes are estimated by Bayesian inference. The prior distributions of the elasticities of flood quantiles to the drivers are estimated by hydrological reasoning and from the literature. The attribution model is applied to European flood and covariate data and aims at attributing the observed flood trend patterns to specific drivers for different return periods at the regional scale. We analyse flood discharge records from 2370 hydrometric stations in Europe over the period 1960–2010. Extreme precipitation, antecedent soil moisture and snowmelt are the potential drivers of flood change considered in this study. Results show that, in northwestern Europe, extreme precipitation mainly contributes to changes in both the median (q2) and 100-year flood (q100), while the contributions of antecedent soil moisture are of secondary importance. In southern Europe, both antecedent soil moisture and extreme precipitation contribute to flood changes, and their relative importance depends on the return period. Antecedent soil moisture is the main contributor to changes in q2, while the contributions of the two drivers to changes in larger floods (T>10 years) are comparable. In eastern Europe, snowmelt drives changes in both q2 and q100.
Highlights
There is widespread concern that river flooding has become more frequent and severe during the last decades and that human-induced climate change and other drivers will further increase flood discharge and damage in many parts of the world (IPCC, 2012; Hirabayashi et al, 2013)
In southern Europe, both antecedent soil moisture and extreme precipitation contribute to flood changes, and their relative importance depends on the return period
In this study we focus on flood quantiles in order to explicitly model the relationships between small and large floods and potential drivers of flood change and to separate the effects of drivers on selected flood quantiles
Summary
There is widespread concern that river flooding has become more frequent and severe during the last decades and that human-induced climate change and other drivers will further increase flood discharge and damage in many parts of the world (IPCC, 2012; Hirabayashi et al, 2013). This concern has given rise to a large number of studies investigating past changes in flood hazard, i.e. changes related to flood discharge, and flood risk, i.e. changes related to damage. Bertola et al.: Regional attribution analysis in Europe not resulted in a clear picture about the contribution of the underlying drivers (for a review on detecting and attributing flood hazard changes in Europe, see Hall et al, 2014)
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