Sea levels along the Brazilian coast are expected to rise in coming decades
June 28, 2017
By Elton Alisson | Agência FAPESP – Sea levels along the Brazilian coast are expected to rise in the decades ahead. However, although more than 60% of the Brazilian population lives in coastal cities, no integrated studies of the vulnerability of these cities to sea level rise and the other effects of climate change, including the increased frequency and intensity of rainfall, have been conducted in Brazil. Research on such topics could be used to estimate the social, economic and environmental damage likely to result from climate change and to prepare action plans to implement adaptive measures.
These are among the conclusions of the special report titled “Vulnerability and adaptation of Brazilian coastal cities to climate change impacts”, which was published by the Brazilian Panel on Climate Change (PBMC) on June 5, 2017, during an event at the Museum of Tomorrow in Rio de Janeiro.
Its publication was supported by FAPESP, and part of the study was based on the Thematic Project, also known as Project Metropolis, as well as other projects supported by FAPESP under its Research Program on Global Climate Change (RPGCC) and the National Science & Technology Institute on Climate Change (INCT-MC), which is funded by FAPESP and the National Council for Scientific & Technological Development (CNPq).
“The report describes a state of the art approach to climate change in coastal cities based on an exhaustive review of Brazilian and international publications on the subject. It also points out gaps in current knowledge to help public policy and decision makers in Brazil propose and implement adaptive measures,” said José Marengo, head of research and development at the Natural Disaster Surveillance & Early Warning Center (CEMADEN) and one of the report’s editors and authors, in an interview with Agência FAPESP.
According to the report, the global average sea level rose by 19 cm between 1901 and 2010, varying in the range of 17-21 cm.
Between 1993 and 2010, the annual average level increased by more than 3.2 mm, with levels varying in the range of 2.8-3.6 mm per year.
Sea levels are also rising along the coast of Brazil, although uncertainty exists regarding the extent of the rise due to the lack of continuous and reliable historical records, the report says.
“We have not yet managed to measure sea level rise in Brazil because there have been few observations and modeling studies to evaluate these impacts,” Marengo said. “However, regional studies show that several medium and large cities are highly vulnerable to any rise in relative sea level and have already been affected by this phenomenon and related events, such as storm surges and floods.”
These cities, where 60% of the population live within 60 km of the coast, include Rio Grande (Rio Grande do Sul), Laguna and Florianópolis (Santa Catarina), Paranaguá (Paraná), Santos (São Paulo), Rio de Janeiro, Vitória (Espírito Santo), Salvador (Bahia), Maceió (Alagoas), Recife (Pernambuco), São Luís (Maranhão), Fortaleza (Ceará) and Belém (Pará).
In São Paulo State and Rio de Janeiro State, for example, average sea level increases of 1.8-4.2 mm have been measured since 1950.
In the city of Santos, where Latin America’s largest port is located, sea levels have risen 1.2 mm per year on average since the 1940s. Additionally, a significant increase in wave height has been observed, increasing from 1 m in 1957 to 1.3 m in 2002, and the frequency of storm surges has also increased.
In the city of Rio de Janeiro, an analysis of data from the tidal gauge on Ilha Fiscal – which provides the longest time series of data in Brazil and is located in the middle of Guanabara Bay – reflected an average sea level rise of approximately 1.3 mm per year based on monthly measurements from 1963-2011 at a 95% confidence level.
In Recife, sea levels rose by 24 cm between 1946 and 1988, representing an average increase of 5.6 mm per year. The report states that coastal erosion and the occupation of land adjoining beach areas have pushed the shoreline more than 20 m inland at Praia de Boa Viagem, the city’s most valuable real estate location.
“Few observations such as these have been made in other parts of Brazil,” Marengo said. “If you try to collect sea level data over the past 40 to 100 years from other cities in the Northeast region, such as Fortaleza, for example, it is very difficult to find any.”
According to the report, climate change and accelerating sea level rise could have severe effects on coastal areas in Brazil.
The socioeconomic effects will be limited to the vicinities of the 15 largest coastal cities, which occupy 1,300 km (17%) of Brazil’s coastline.
The consequences of rising sea levels include increased coastal erosion; increases in the frequency, intensity and magnitude of floods; the increased vulnerability of people and property; and decreased habitable space.
“The most evident impacts of rising sea levels are increasingly frequent coastal floods and shoreline reductions,” Marengo said. “However, there are other less perceptible effects, such as marine intrusion, via which seawater penetrates aquifers and freshwater ecosystems.”
Projections in the fifth assessment report (AR5) of the Intergovernmental Panel on Climate Change (IPCC) estimate a global sea level rise of 0.26-0.98 m by 2100 under the worst-case scenario. The report presents similar projections for the Brazilian coast.
Because the probability of flooding increases as sea levels rise, floods will become more likely in areas where sea levels have risen by more than 40% over the last 60 years, as they have near several major Brazilian coastal cities, the report says.
Coastal floods will be most troublesome in the Northeast, South and Southeast Regions. The southern and southwestern shorelines of the city of Rio de Janeiro may also be affected. The six cities most vulnerable to rising sea levels in Rio de Janeiro State, according to studies presented in the report, are Parati, Angra dos Reis, Rio de Janeiro, Duque de Caxias, Magé and Campos dos Goytacazes.
“Rising sea levels combined with storms and strong winds may severely damage the infrastructures of these cities,” Marengo said.
The report highlights the Santos Municipal Plan for Adaptation to Climate Change as an example of how cities can develop action plans to adapt to climate change and mitigate the associated effects (read more on the subject at agencia.fapesp.br/22129).
The plan is based on the findings of Project Metropolis, which was coordinated by Marengo.
The international study estimated potential damages of almost R$2 billion by 2100 unless adaptive measures are taken. These projected damages are associated with coastal flooding in southeastern and northwestern Santos caused by sea level rise, storm surges, astronomical and meteorological tides and extreme climate events.
The study was conducted by researchers affiliated with CEMADEN, the National Space Research Institute (INPE), the Geological Institute (IG), the University of São Paulo (USP) and the University of Campinas (UNICAMP) in partnership with colleagues at the University of South Florida (USA) and King’s College London (UK), as well as technical staff employed by the city of Santos.
“We plan to apply the methodology used in Santos to other Brazilian coastal cities to obtain at least an initial estimate of the cost of adapting to rising sea levels,” Marengo said.
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