River floods (CLIM 017) - Assessment published Nov 2012
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Climate change (Primary topic)
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)
- CLIM 017
Key policy question: What is the trend in river floods across Europe?
- More than 325 major river floods have been reported for Europe since 1980, of which more than 200 have been reported since 2000.
- The rise in the reported number of flood events over recent decades results mainly from better reporting and from land-use changes
- Global warming is projected to intensify the hydrological cycle and increase the occurrence and frequency of flood events in large parts of Europe. However, estimates of changes in flood frequency and magnitude remain highly uncertain. In regions with reduced snow accumulation during winter, the risk of early spring flooding would decrease.
Projected change in river floods with a return period of 100 years
Note: Projected change in the level of a 100-year maximum level of river discharge between the reference period 1961–1990 and the 2020s (left), 2050s (centre) and 2050s (right) based on an ensemble of 12 RCM simulations with LISFLOOD for the SRES A1B scenario.
- Climate Adaptation – modelling water scenarios and sectoral impacts provided by Euro-Mediterranean Centre on Climate Change (CMMC)
Figure 1 shows the occurrence of flood events in Europe from 1998–2009. This picture is incomplete because events with small spatial extent and/or impact are not included. Nevertheless, it becomes clear that large areas throughout Europe have been affected by flooding over the last decade, many of them even multiple times. Flood losses in Europe have increased substantially over recent decades but this trend is primarily attributable to socio-economic factors, such as increasing wealth located in flood zones. The influence of anthropogenic climate change remains inconclusive [i].
Significant trends in river inundations have been identified in some regional and national studies. For example, significant increases in flood intensities have been identified between 1951 and 2002 in western, southern and central Germany [ii] as well as in upland catchments in the northern and western UK [iii]. A new analysis of the strong UK floods of 2000 suggests that anthropogenic climate change was a contributing factor [iv]. In the Alps [v] and Nordic region [vi], snowmelt floods have occurred earlier because of warmer winters. In contrast, no conclusive evidence was found in an analysis of flood trends in Austria [vii], and an increasing flood trend in Catalonia is attributed to socio-economic factors [viii].
Changes in future flood hazard in Europe have been simulated by a hydrological model driven by an ensemble of climate simulations [ix]; [x]. An increasing flood hazard is consistently projected for several of Europe’s major rivers across climate models and emissions scenarios [xi].
Figure 2 shows the change in the return period of a 1-in-a-century flood between the reference period and 2050 based on an ensemble of 11 climate and hydrological simulations. Red rivers indicate a decrease in the return period, which implies that floods of this magnitude will occur more frequently in the future. While the ensemble mean presented in Figure 2 provides the best assessment of all model simulations together, individual simulations can show important differences from the ensemble mean for individual catchments, partly due to significant decadal-scale internal variability in the simulated climate [xii]. A decrease in 1-in-a-century floods is projected in large parts of north-eastern Europe due to a reduction in snow accumulation and hence melt-associated floods under milder winter temperatures [xiii]. This projection is consistent with other studies on snow-dominated regions, including parts of Finland [xiv], the Alps and Carpathian Mountains [xv]. Flash floods and pluvial floods, which are triggered by local intense precipitation events, are also likely to become more frequent throughout Europe [xvi]. A regional approach is required for solving pluvial and fluvial flood problems in urban areas [xvii] because regional and local city characteristics are very important in determining the impacts from projected increases in floods and intensive precipitation events. Flood risks in a city can also be strongly influenced by factors outside the city boundaries such as upstream river management.
[i] J.I. Barredo, „Normalised flood losses in Europe: 1970–2006“, Natural Hazards and Earth System Sciences 9 (Februar 9, 2009): 97–104, doi:10.5194/nhess-9-97-2009.
[ii] Theresia Petrow and Bruno Merz, „Trends in flood magnitude, frequency and seasonality in Germany in the period 1951–2002“, Journal of Hydrology 371, Nr. 1–4 (Juni 5, 2009): 129–141, doi:10.1016/j.jhydrol.2009.03.024.
[iii] Jamie Hannaford and Terry J Marsh, „High‐flow and Flood Trends in a Network of Undisturbed Catchments in the UK“, International Journal of Climatology 28, Nr. 10 (August 1, 2008): 1325–1338, doi:10.1002/joc.1643.
[iv] Pardeep Pall et al., „Anthropogenic Greenhouse Gas Contribution to Flood Risk in England and Wales in Autumn 2000“, Nature 470, Nr. 7334 (Februar 16, 2011): 382–385, doi:10.1038/nature09762.
[v] B. Renard et al., „Regional methods for trend detection: Assessing field significance and regional consistency“, Water Resources Research 44 (August 12, 2008): W08419, doi:10.1029/2007WR006268.
[vi] Donna Wilson, Hege Hisdal, and Deborah Lawrence, „Has streamflow changed in the Nordic countries? – Recent trends and comparisons to hydrological projections“, Journal of Hydrology 394, Nr. 3–4 (November 26, 2010): 334–346, doi:10.1016/j.jhydrol.2010.09.010.
[vii] Gabriele Villarini et al., „Analyses of Extreme Flooding in Austria over the Period 1951–2006“, International Journal of Climatology 32, Nr. 8 (2012): 1178–1192, doi:10.1002/joc.2331.
[viii] M. Barnolas and M.C. Llasat, „A flood geodatabase and its climatological applications: the case of Catalonia for the last century“, Natural Hazards and Earth System Sciences 7, Nr. 2 (April 5, 2007): 271–281, doi:10.5194/nhess-7-271-2007.
[ix] Rutger Dankers and Luc Feyen, „Flood hazard in Europe in an ensemble of regional climate scenarios“, Journal of Geophysical Research 114, Nr. D16 (August 27, 2009), doi:10.1029/2008JD011523.
[x] Martina Flörke et al., Climate Adaptation – modelling water scenarios and sectoral impacts. Final Report Contract N° DG ENV.D.2/SER/2009/0034 (Kassel, Germany: Center for Environmental Systems Research, University of Kassel, Oktober 28, 2011), http://circa.europa.eu/Public/irc/env/wfd/library?l=/framework_directive/climate_adaptation/climwatadapt_report.
[xi] Luc Feyen et al., „Fluvial flood risk in Europe in present and future climates“, Climatic Change 112, Nr. 1 (November 23, 2011): 47–62, doi:10.1007/s10584-011-0339-7.
[xii] Feyen et al., „Fluvial flood risk in Europe in present and future climates“.
[xiii] Dankers and Feyen, „Flood hazard in Europe in an ensemble of regional climate scenarios“.
[xiv] Noora Veijalainen et al., „National scale assessment of climate change impacts on flooding in Finland“, Journal of Hydrology 391, Nr. 3–4 (September 24, 2010): 333–350, doi:10.1016/j.jhydrol.2010.07.035.
[xv] EEA, Regional climate change and adaptation — The Alps facing the challenge of changing water resources EEA Report (Copenhagen, September 9, 2009), http://www.eea.europa.eu/publications/alps-climate-change-and-adaptation-2009.
[xvi] J. H Christensen and Ole B. Christensen, „Severe summertime flooding in Europe“, Nature 421 (Februar 20, 2002): 805–806; Zbigniew W. Kundzewicz, Maciej Radziejewski, and Iwona Pínskwar, „Precipitation extremes in the changing climate of Europe“, Climate Research 31 (Juni 26, 2006): 51–58, doi:10.3354/cr031051.
[xvii] EEA, Urban adaptation to climate change in Europe - Challenges and opportunities for cities together with supportive national and European policies EEA Report (Copenhagen: European Environment Agency, 2012), http://www.eea.europa.eu/publications/urban-adaptation-to-climate-change.
provided by Dartmouth Flood Observatory
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