Rio de Janeiro bay reforestation shows mangroves' power to mitigate climate disasters

At the rear of Rio de Janeiro's polluted Guanabara Bay, thousands of mangroves rise as tall as 13 feet (about 4 meters) from a previously deforested area.

The 30,000 trees, planted by non-profit organization Instituto Mar Urbano over four years in the Guapimirim environmental protection area, stand as an example for cities seeking natural means to improve climate resilience.

Such ecosystems are vital for protection against floods that have become increasingly frequent around the world. Brazil's southern state of Rio Grande do Sul is still reeling from a devastating flood earlier this month that wreaked havoc and took lives, with waters far from subsiding to normal levels.

Mangroves slow sea water's advance into riverbeds during storm surges by soaking it up, and protects the land by stabilizing soil that otherwise could be washed away. They also act as a carbon sink. The reforestation in Rio's bay improved the cleanliness of water that's a breeding ground for marine species. Crabs have returned, providing extra income for the local crab pickers who helped plant the trees.

"To plant a tree in this mangrove is an act of environmental recovery and also an act in the fight against climate change," Ricardo Gomes, a director at the non-profit, told The Associated Press on Thursday. "Today we can be sad, because of all that has been lost (in Brazil's South), all that was destroyed. But we never had so much knowledge, so much technology and resources to recover our environment."

A lack of mangroves wasn't the cause of flooding around Rio Grande do Sul's capital, Porto Alegre, that sits beside a lagoon. The flooding largely stemmed from water that flowed down rivers into the area.

The coastal risk map created by Climate Central, a nonprofit science research group, forecasts areas west and north of Porto Alegre will be underwater by 2100. In Rio, it shows two large areas in the back of its bay — one of which includes the Guapirimim protected area — will be underwater by 2050. That underscores the need for action to mitigate sea water's encroachment.

Natural vegetation like that of Guapimirim "is like a true sponge," avoiding or mitigating floods by reducing the energy of the waters, Mauricio Barbosa Muniz, the manager of a reserve at Brazil's federal agency Chico Mendes Institute for Biodiversity Conservation, said. Vegetation in the region safeguards 1 million residents in the city of Sao Goncalo, in Rio's metropolitan region, and others.

"In places that were occupied irregularly, such as cities, it is possible to restore those areas and make human settlements that are resilient and prepared for the effects of climate change," Muniz said.

Since 2000, flood-related disasters across the planet have increased by 134% over the two previous decades, according to a 2021 report by the World Meteorological Organization.

Environmentalists say the loss of natural vegetation due to agriculture and cattle ranching in Rio Grande do Sul state amplified the flooding. A recent study by MapBiomas, a network that includes non-profit organizations, universities and start-ups, says the Brazilian state lost 22% of its native vegetation between 1985 and 2022, equal to an area greater than the U.S. state of Maryland.

Federal, state and municipal authorities seem to be in agreement since tragedy struck that a massive reforestation effort will be needed in Rio Grande do Sul, but the scope of the investment and specific initiatives are yet to be announced.