Improving natural risk management for future floods

While risk management has reduced communities’ vulnerability to flood and droughts, these events continue to having an increasing worldwide impact, according to a study published in the journal Nature.

This intensification of the impact of natural phenomena is particularly noticeable when a region with a recorded prior event — rain, flood, or drought— begins to experience a second event with a higher degree of hazard.

“This results from the fact that the improvement in management has been based on the parameters of previous episodes, but it has not been designed to cope with such extreme events. The difficulty observed in managing unprecedented events is alarming, especially if we consider that, as a result of the climate change, the hydrological events that are projected are becoming increasingly extreme”, notes researcher Maria del Carmen Llasat, a professor of Atmospheric Physics at the Faculty of Physics and member of the Water Research Institute of the University of Barcelona.

Flood and Drought Episodes Worldwide

The study, led by the Heidi Kreibich, from the German Research Centre for Geosciences (GFZ), includes the participation of nearly a hundred experts from the International Association of Hydrological Sciences (IAHS).

The study analyzes 29 pairs of flood episodes and 15 cases drought episodes in different areas of the world. The aim is to check how these factors involved in risk have changed between the first and the second episode, generally occurring more than ten years apart, but in the same place.

In the case of Catalonia, the study compared pluvial floods in Barcelona that occurred on 21 September 1995 and on 6 September 2018, and the recorded droughts in the periods 1986-1989 and 2004-2008. To carry this comparative analysis out, the researchers worked in collaboration with Barcelona Water Cycle (BCASA) the Ebro Observatory (URL-CSIC).

Barcelona City, a Successful Case

The international study has recorded only two success stories — Barcelona and Central Europe — in natural hazard management, out of the 29 pairs of flood events analyzed worldwide. In these cases, the hazard of the second recorded event was higher than that of the first, but the recorded damage was lower.

In the case of Barcelona, following the 1996 floods, the city promoted a plan that culminated in the construction of 15 rainwater retention basins and the improvement of the entire flood prevention and management system.

"The improvements in Barcelona's rainwater network over the last twenty years have been decisive in alleviating the effects of floods in the city. In fact, while in the Metropolitan Area of Barcelona there has been a slight increase in flooding since 1981, this trend is negative in Barcelona. However, this is not enough", notes Llasat. "The permeability of the soil should be increased with paving that allows rain to filter through, more areas should be set aside for green spaces and streets and drains should be kept clean. However, there are still neighborhoods with major flooding problems where it is difficult to take structural action, such as stormwater tanks. In these cases, it is necessary to look for solutions that require citizen participation and awareness of this type of event.”

Finding these solutions that require citizen participation is the challenge faced by the Individual Change of Habits Needed for Green European transition (I-CHANGE) project, in which the University of Barcelona is participating.

Flood management in Germany and Austria is the other success story described in the article. Two common factors stand out in the successful strategies of Barcelona and Central Europe: the improvement of risk management governance — more integration in emergency management and early warning systems — and the implementation of a series of structural measures that required high investment (the stormwater reservoirs in Barcelona or the construction of dykes in Central Europe).

How to Improve Natural Risk Management

Efforts to promote more operational and effective responses to these extreme events face a number of obstacles

"Large investments such as those made in the city of Barcelona or in Central Europe are not possible for everyone. In fact, they would not be desirable either. Recent studies have shown that they can lead to a false sense of security (especially in the case of river flooding), as they increase the occupation of flood zones and thus the associated risk,” says Llasat. “Despite structural improvement, the United Nations consider that Barcelona is not doing enough to raise awareness of the risk of flooding among its inhabitants, nor among visiting people. This is a widespread problem.”

Improving governance, applying nature-based solutions and involving citizens are the global key actions for mitigating the effects of natural hazards worldwide, in a context of sustainable development.