A team of Newcastle University researchers have released a study that assesses the future changes in flood, heatwaves, and drought impacts for 571 European cities, finding that heatwave days will increase across all cities. Additionally, the high-end climate change scenario projects that most cities will see increases in both drought and river flood risks.

Over 75 per cent of the European Union’s population lives in urban areas, and this percentage is expected to grow to 82 per cent by 2050. Needless to say, it’s important to know how droughts, heat waves, and floods in European cities will change.

In all cities more frequent and hotter heat waves: In this study, heat waves are defined as three consecutive days where both maximum and minimum temperatures exceed the upper five per cent of these values for the historical period. According to the results, all European cities will experience more frequent and hotter heat waves. The cities in Southern Europe see the largest increase in the number of heat wave days, possibly up to 69 per cent. Projected increase of maximum temperature during heat waves is largest in central European cities, however, even up to 14°C (for Innsbruck in Austria). In this part of Europe, both infrastructure and populace are generally not adapted to extreme heat.

Future droughts much worse in cities Southern Europe: The severity of a drought is defined in this study as the accumulated precipitation deficit relative to mean annual rainfall. Southern European cities will see an increase in drought conditions: Future droughts may get up to 14 times worse than the ones in the historical period. To a certain extent, this region may be adapted to drought. The projected upper level of change is likely to be beyond breaking point in many cases, however. This supports recent analysis of the potential for a mega drought in major Iberian water resource regions. For mid and northern latitude cities it is very unlikely that droughts will get much worse than the ones in the historical period.

More river flooding in cities northwest Europe: In this study, a flood is defined as the maximum discharge that occurs once every 10 years on average. Floods were only considered for cities with a river that has a catchment area of at least 500 km2. Increases in river flooding are most prevalent in north-western Europe, and are particularly worrying for the British Isles and several other European cities, which could observe more than a 50 per cent increase of their 10-year-high river flow. One should be aware, however, that snowpack and melting processes are not accounted for in this study; this may affect the results for Scandinavian and Alpine cities.

Top 100 cities with hazards: Capital cities that are among the top 100 for one or more hazards according to this study, are Dublin, Helsinki, Riga, Vilnius, and Zagreb for river flooding, Stockholm and Rome for the increase of the number of heat wave days, Prague and Vienna for the increase of maximum temperature during heat waves, Lisbon and Madrid for droughts, and Athens, Nicosia, Valleta, and Sofia for both the number of heat wave days and the severity of droughts.

Adapting cities to heat waves is complicated: We know a lot about the benefits of adapting to flood risk. Adapting cities to heat waves is more complicated, both in design and with respect to quantifying benefits and costs. In Southern Europe, adapting to some of the projected changes could only be achieved by a fundamental, and expensive, re-engineering of each city or water resource system, as significant adaptation to climate extremes has already been implemented and radical changes will be needed to achieve more. In Central Europe, by contrast, there should be capacity and economic resources to support adaptation.

 

Figure above: (a) Cities whose changes are in the top 50% for all indices (i.e. changes in number of heat-wave days, changes in maximum daily maximum temperature for days classified as heat-waves days, changes in probability for any given month in the future being above the historical maximum DSI-12, maximum DSI-12 change factor and, for the cities with rivers, changes in Q10 ratio). (b) Cities whose changes are on the bottom 50% for all indices. (c) Cities whose changes in both flooding and maximum temperature during a heat-wave indices are in the top 25%. (d) As (c) but for both drought indices and changes in number of heat-wave days. Changes are calculated between the historical period (1951–2000) and the future period (2051–2100) for the high-impact scenario. Flood risk was analysed if the maximum flow accumulation cell within the city corresponded to a catchment area of at least 500 km2 (i.e. city ‘with river’). From Guerreiro et al. 2018.

Credit: https://dailyplanet.climate-kic.org/future-heat-waves-droughts-floods-571-european-cities/

Full article: Guerreiro et al. 2018. Environmental Research Letters 13. 


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