Rio Maps Flood Risk to Avert Annual Disaster

  • by Fabiana Frayssinet (rio de janeiro)
  • Tuesday, January 29, 2013
  • Inter Press Service

The initiative was put forward by the Rio de Janeiro State Secretariat of Environment, and must still be approved by the Legislative Assembly of the State of Rio de Janeiro. It was announced in the midst of yet another weather-related disaster in the state, earlier this month.

Since the beginning of the year, the southern hemisphere summer rainy season has already resulted in at least three deaths, while thousands of people have been left homeless due to collapsed buildings and flooding.

"We decided to submit this bill to the legislative assembly to bring an end to the suicidal ‘populism' of some mayors, who ignore the maps of disaster risk areas," Rio de Janeiro Environment Secretary Carlos Minc told IPS.

"I have seen mayors building streets and installing public services in places that have been identified by studies as vulnerable to natural disasters, which imminently endangers the lives of these populations," said Minc.

If the bill is passed into law, disaster risk maps will become official public documents and "municipal governments will be obliged to incorporate their findings and restrictions in master plans and regulations on land use," he added.

A study by the Rio de Janeiro State Geological Service, reported by the newspaper O Globo this month, revealed that there are disaster risk areas in 67 of the state's 92 municipalities, and there are some 36,000 people living in these highly vulnerable areas.

In an interview with IPS, geotechnical engineer Willy Lacerda noted that most of these municipalities are in mountainous areas, which makes them susceptible to landslides during heavy rainfall.

Lacerda, an engineering professor at the Federal University of Rio de Janeiro, explained that different rainfall patterns can lead to different types of disasters.

In the case of steady, continuous rainfall, the ground slowly becomes saturated with water. "If the depth of this saturation is great enough, there may be scattered landslides," he noted.

When there is heavy rainfall following a period of continuous precipitation, rivers can become swollen and overflow. The riverbanks are more susceptible to being washed out because the soil has become saturated and therefore less resistant to the water pressure.

"In this case, landslides are widespread," he said.

This is what happened in 2011 in Teresópolis and Nova Friburgo, in the mountainous region of Rio de Janeiro. Flooded rivers and collapsed buildings resulted in 900 deaths and left some 25,000 people homeless, according to figures from the Rio de Janeiro state government.

A third variant is that of torrential rains of more than 60 millimetres an hour, which can set off widespread landslides on steep slopes, as was the case in Jacarepaguá in 1996.

Disaster risk mapping contributes to preventing or at least minimising climate-related tragedies, stressed Lacerda. In some cases, it could lead to the timely evacuation of the population from vulnerable areas. In others, it might bring about engineering works, such as containment walls to reinforce hillsides.

Lacerda, who participates in the development of these maps, explained that they take numerous factors into account, such as geology, the shape of the terrain (slope and concavity), the thickness and resistance of the topsoil, and the type of vegetation.

"This is how we define areas where there is a greater or lesser probability of landslides, and based on this, we determine which homes are more susceptible to landslides," on a scale of high, medium and low risk, he said.

The risk of flooding, meanwhile, can be gauged on the basis of local hydrologic conditions and data like maximum and average rainfall.

None of these efforts, however, could prevent the catastrophic effects of a torrential downpour like the one that hit Vale de Cuibá, in the district of Itaipava, en 2011, and Xerém, in Duque de Caxias, earlier this month, washing away houses, bridges and cars "like a tsunami", said Lacerda. Nevertheless, the impact of these disasters could be mitigated, he added.

Disaster risk maps also make it possible to identify areas where housing can be constructed to shelter people evacuated from high-risk areas.

The government of the city of Rio de Janeiro, the state capital, has installed sirens in neighbourhoods located in high-risk areas, including a number of its favelas or shantytowns. The sirens are activated six hours before the expected arrival of heavy rains.

For its part, the national government announced that it will allocate some 175 million dollars for construction projects to reinforce slopes in order to prevent landslides.

The state of Rio de Janeiro has already allocated resources for these types of public works, but in some municipalities the funds were reportedly misappropriated by corrupt mayors.

In Xerém, for example, trash collection had been interrupted before the devastating downpour due to a change of municipal government and reported irregularities in the contracting of the company responsible for urban sanitation.

While the accumulation of trash obviously did not cause the downpour, said Lacerda, it did aggravate its impact, because it obstructed the drainage of the rainwater and contributed to the spread of diseases.

Brazilian theologian and environmental activist Leonardo Boff, in a column published after the disaster in Xerém, classified the "tsunami" that devastated the municipality as a "crime against humanity", like the other socio-environmental disasters that have become ever more frequent.

Boff proposed "a national law on socio-environmental responsibility… with heavy penalties for those who do not respect it.

"We are irresponsible towards nature when we deforest, when we dump billions of litres of toxic agrochemicals into the soil, when we release around 30 billion tonnes of greenhouse gases into atmosphere annually, when we pollute the water, when we destroy the forests along riverbanks," declared Boff.

Moreover, "we do not respect the slope of mountains that can crumble and kill people, nor do we consider the banks needed by rivers so that floods do not wash everything away with them," he added.

*This story was originally published by Latin American newspapers that are part of the Tierramérica network. Tierramérica is a specialised news service produced by IPS with the backing of the United Nations Development Programme, United Nations Environment Programme and the World Bank.

© Inter Press Service (2013) — All Rights ReservedOriginal source: Inter Press Service

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