Increasingly heavy rains cause flash floods in an “over-urbanized” area

The heavy rains caused by Storm Boris have flooded Central and Eastern Europe. They have caused more than 25 deaths in Romania, Poland, Austria and Germany. When it reached Italy, it left two people missing and 1,000 others evacuated. Spain knows well how hard floods hit. Without going any further, it is the most costly and deadly natural disaster – if we do not count heat waves. The climate reality is forcing Spain to adapt its territory, which is particularly vulnerable because super-urbanizedto the increase in flash floods caused by increasingly heavy rains generated by global warming.

The starting point is that “the increase in intense storms and impermeable surfaces due to overdevelopment has led to an increase in urban areas affected by flooding.” Especially in the southeast of Spain, this dynamic has caused “greater exposure and vulnerability of the population to new risks,” according to a study group from the University of Alicante.

How to stop or at least mitigate a flood of water at full speed and loaded with mud or debris? How to minimize the damage?

The EU’s Joint Research Centre (JRC) proposes four solutions: retention areas, dikes, flood protection and relocation of people.

Additionally, urban drainage systems (such as permeable sidewalks, rain gardens, and filter drains) can capture rainwater to prevent runoff, which is rainwater that is not absorbed by the ground and forms rivers on roads that carry cars and people along during episodes of severe storms.

Strengthening the dikesby increasing its height, “can be effective”, explain the conclusions of the JRC, although the benefit varies considerably depending on the country and in Spain, they point out, it is only about 6% (in Luxembourg it exceeds 80%). “We must take into account – they add – that the raising of the dikes can have negative environmental and social consequences, because it can increase the magnitude of the current downstream, thus increasing the danger and risks in these areas. In Hungary, 754 kilometres of dikes were raised this week to stop the “flood of the decade”, a consequence of the passage of Boris.

Furthermore, “it promotes the loss of memory.” This means that by reducing the frequency of floods, a sense of security is generated: “if the defenses fail, it will lead to catastrophic consequences.” In this sense, the analysis of the professor of the University of Barcelona María del Carmen Llasat Botija highlights the effect of the paradox of development that “attracts new settlements and goods to areas that are apparently protectedincreasing exposure and creating a sense of false security.

Regarding buildingsIt is recommended that buildings be fairly watertight or at least watertight up to the expected flood height. The idea also includes that liquid can enter and exit easily and that there is elevation for “important goods”.

In this sense, the engineer specialized in hydrogeology from the University of Alicante, Javier Valdés, clarified to elDiario.es that, although the damage due to floods increases with depth, “they are much greater from 70 or 80 centimeters, more or less the height of the tables, because up to this height many goods can be saved, but from there the damage skyrockets.

Move the population This is a measure of “last resort”, as it generates high costs. [hay que proporcionar a los afectados nuevas viviendas] and has low social acceptance. However, the study indicates that Spain is one of the few countries in which this relocation can be economically efficient, which indicates, they point out, “that the costs of flooding can be as high as the construction of new houses.”

Although it may seem like a distant solution, this solution has already been applied in Spain. In the Valencian city of Ontinyent, the Canterería neighborhood was relocated due to the destructive flooding episodes of the Clariano River. In this area, it is planned to build a river park, that is, a retention area.

Awareness

Mediterranean floods tend to be more “sudden”, caused by heavy rains that can be local, producing flash floods “in the context of a major flood”, describes the work of Professor María del Carmen Llasat Botija. These extreme weather events are multiplying in Spain. With them, the danger increases by concentrating a large amount of water in a short time. And in more vulnerable terrains because flood zones are increasingly occupied by homes and infrastructure, which multiplies the risks of damage, whether material or personal.

However, the atmospheric physics professor’s analysis adds emergency plans and “improving society’s perception of risk” as elements of adaptation.

In this sense, greater knowledge and awareness “should improve risk perception and individual and social empowerment,” he describes. This involves “teaching people how to behave in the event of a flood and avoid risky situations, such as driving in floodwaters or swimming in a flooded river. In fact, the physicist highlights in her work that what has increased the most are floods with one or two victims. [más que las altamente mortales] ” due to reckless behavior fostered by ignorance of danger and growing confidence in technology.

Country exposed

Spain is a territory highly exposed to flooding. The sections presenting a clear risk total almost 12,000 km, according to the latest measurements from the Ministry of Ecological Transition. The danger affects more than 2.3 million people in the basins managed by the Ecological Transition, as evidenced by the latest risk management plans approved by the government – ​​these remain the exclusive responsibility of the autonomous communities.

“Appropriate flood risk reduction strategies can minimise the danger,” warn the JRC experts. Among the conclusions of the Joint Research Centre, it emerges that to reduce this risk, “the combination of different measures that work together in river basins is probably the best strategy to maximise the benefits of these measures.”