Brazilian institute develops methodology to map risk of landslides

System based on free data and software could help city governments that lack surveys of vulnerable areas.

By Elton Alisson

Agência FAPESP – Researchers at the National Space Research Institute (INPE) in Brazil have developed a methodology to map city areas susceptible to landslides using data and software in the public domain.

Developed within the ambit of the Thematic Project “Assessment of impacts and vulnerability to climate change in Brazil and strategies for adaptation options” supported by FAPESP, the methodology was described in an article published in the journal Natural Hazards and Earth System Sciences.

“The point of using free software and data is to enable the methodology to be used in a practical and reliable way by municipal governments that don’t have their own maps of landslide-susceptible areas that often suffer from this kind of problem,” said Pedro Ivo Camarinha, a PhD student affiliated with INPE and one of the authors of the methodology.

The methodology uses a georeferenced information processing system called SPRING, developed by INPE and available on the Internet free of charge, as well as Topodata, a geomorphometric database covering Brazil and also created by INPE using data from the Shuttle Radar Topography Mission (SRTM).

Carried out in February 2000 by NASA’s space shuttle Endeavour, the SRTM was an international research effort that generated the most complete laser-based high-resolution digital topographic database of Earth.

“Topodata improved the resolution of the topographic data provided by the SRTM, which was 90 m, for all of South America and especially Brazil, offering users a topographic dataset with a spatial resolution of 30 m,” Camarinha told Agência FAPESP.

“This is very helpful if you’re interested in producing landslide-susceptibility maps for Brazilian municipalities with an acceptable level of resolution.”

Serra do Mar

A first test of the methodology’s reliability consisted of an estimate of landslide susceptibility and hazards in Caraguatatuba, Ubatuba, Santos and Cubatão. These four municipalities located in the Serra do Mar region on the coast of São Paulo State are strategically important to the state and national economies because of the ports, roads and oil and gas pipelines located there. They are also tourism centers. Natural disasters involving landslides are frequent in the area owing to its geophysical characteristics. The problem is compounded by disorderly population growth leading to the occupation of hillsides, slopes and other land subject to instability.

For these reasons, the four cities concerned have been considered priorities for the landslide hazard mapping projects conducted by CPRM, the National Geological Service. As Brazil’s official agency for gathering data and information on geology, minerals and water resources, CPRM offers city governments and civil defense units assistance with natural disaster risk management.

“The authorities in Caraguatatuba, Ubatuba, Santos and Cubatão already have maps of landslide-susceptible areas supplied by CPRM because of their history of natural disasters relating to this kind of geological process,” Camarinha said.

The researchers compared the survey of landslide-susceptible areas produced using the methodology developed by INPE with CPRM’s landslide hazard survey of these four municipalities, and concluded that INPE’s methodology is highly efficient.

In addition to the landslide hazard areas already identified by CPRM in the field, the methodology pointed to areas with high and very high susceptibility, mostly where urban growth has been rapid.

“The methodology we developed showed very precisely where the landslide hazard areas are located in each of the four municipalities analyzed,” Camarinha said.

“It can be used both in cities that already have landslide susceptibility maps, to reinforce and guide CPRM’s on-site analysis, and by those that don’t have surveys of this kind.”

National survey

According to the International Emergency Event Database (EM-DAT), which holds data on natural disasters occurring worldwide since 1900, 150 major natural disasters were reported in Brazil in the period 1900-2013. They affected 71 million people, caused more than 10,000 deaths and led to losses estimated at US$16 billion.

In light of the increasing frequency and intensity of landslide-related natural disasters in Brazilian cities in the last two decades, especially in the Southeast and South regions, in 2013 the federal government commissioned CPRM to begin mapping susceptibility, hazards and risks in 821 municipalities considered priorities because the largest number of problems had occurred there.

The survey has proceeded since then, but several prioritized municipalities have not yet been mapped, according to Camarinha.

“In addition to the cities that are considered priorities, there are a number of others where landslides have also occurred, albeit less frequently and intensely,” he said.

“For these cases, the methodology we developed can assist civil defense units and city government departments responsible for dealing with natural disasters in their efforts to improve urban planning and identify landslide hazard areas.”

In addition to Caraguatatuba, Ubatuba, Santos and Cubatão, some 60 other cities in the state were surveyed for landslide susceptibility using the methodology once it had been validated. These other cities are located in the areas known as Baixada Santista (south coast of the state), North Coast, Metropolitan Campinas, Serra da Mantiqueira and Paraíba Valley.

The researchers are also evaluating the possibility of adapting the methodology to map flood-prone areas. Flooding is the most frequent type of natural disaster in Brazil (58% of the total) and causes the most deaths, followed by landslides (15.6%), according to the Brazilian Atlas of Natural Disasters produced by the Federal University of Santa Catarina’s Disaster Research Center (UFSC-CEPED).