Flood trends in Europe: are changes in small and big floods different? [post]

Miriam Bertola, Alberto Viglione, Julia Hall, Günter Blöschl
2019 unpublished
<p><strong>Abstract.</strong> Recent studies have revealed evidence of trends in the median or mean flood discharge in Europe over the last five decades, with clear and coherent regional patterns. The aim of this study is to assess whether trends also occurred for larger return periods accounting for the effect of catchment scale. We analyze 2370 flood records, selected from a newly-available pan-European flood database, with record length of at least 40 years over the period
more » ... rs over the period 1960–2010 and with contributing catchment area ranging from 5 to 100 000 km<sup>2</sup>. To estimate regional flood trends, we use a non-stationary regional flood frequency approach consisting of a regional Gumbel distribution, whose median and growth factor can vary in time with different strengths for different catchment sizes. A Bayesian Monte Carlo Markov Chain (MCMC) approach is used for parameter estimation. We quantify regional trends (and the related sample uncertainties), for floods of selected return periods and for selected catchment areas, across Europe and for three regions where coherent flood trends have been identified in previous studies. Results show that, in the Atlantic region, the trends in flood magnitude are generally positive. In small catchments (up to 100 km<sup>2</sup>), the 100-year flood increases more than the median flood, while the opposite is observed in medium and large catchments, where even some negative trends appear, especially over the southern part of the Atlantic region. In the Mediterranean region flood trends are generally negative. The 100-year flood decreases less than the median flood and, in the small catchments, the median flood decreases less compared to the large catchments. Over Eastern Europe the regional trends are negative and do not depend on the return period, but catchment area plays a substantial role: the larger the catchment, the more negative the trend. The process causalities on the effects of return period and catchment area on the flood trends are discussed.</p>
doi:10.5194/hess-2019-523 fatcat:zipisiu4zzfrvoohzv7maq6bym