Flood-mitigation infrastructure built in the southern Philippines for more than $100 million by clearing native vegetation could exacerbate flood risk in the future, reports Mongabay’s Keith Anthony Fabro.
In 2011, floods and landslides caused by Tropical Storm Washi, known locally as Sendong, killed more than 1,260 people in the cities of Cagayan de Oro and Iligan. The disaster prompted the government to spend 8.5 billion pesos ($144 million) to build flood-mitigation infrastructure like dikes, flood walls and drainage inlets between 2019 and 2023. These are meant to protect 614 hectares (1,517 acres) of area from flooding caused by the overflowing Cagayan de Oro River.
Experts and residents told Fabro that the structures have brought people a sense of security, but the construction has come at an environmental cost.
Many trees were damaged, Mary Lynne Cananea, Cagayan de Oro’s environmental conservation and rehabilitation section chief, told Fabro. She added the project was handled by national agencies, and her office hadn’t received details on the species and number of trees that were cut.
An analysis by Mongabay found that 26 hectares (65 acres) of vegetation were lost from January 2019 to December 2023 during the project’s construction, resulting in 40% tree cover reduction within a 100-meter (330-foot) radius of the flood-control structures. Experts told Mongabay this can undermine the project’s future flood mitigation potential.
Residents along Macajalar Bay, where trees were cleared for a mile-long dike evacuation road, told Mongabay that the area had contained nipa palms that had once protected them from the onslaught of Washi.
Mary Jean Salvaña, environmental science professor at the University of Science and Technology of Southern Philippines, told Mongabay that “the decline of nipa mangroves may diminish their capacity to buffer coastal communities during severe flooding and storm surges in the long run.”
Fabro writes that studies show that while flood-mitigating structures are important, preserving tree cover is key to intercepting runoff.
Angela Grace Toledo-Bruno, environmental science professor at Central Mindanao University, said removing vegetation within riparian ecosystems, or land by the edge of water bodies, can result in “disasters.”
Worldwide, mangrove forests are vanishing despite their crucial role in flood mitigation.
Fabro found that mangrove forest cover in the Philippines declined by around 100,000 hectares (250,000 acres) from 1920-2020. In Macajalar Bay, mangrove cover decline from an estimated 325 hectares in 1950 to 202 hectares by 2020, or about 800 acres to 500 acres.
Henry Adornado, regional director of the Department of Environment and Natural Resources, told Mongabay they need to verify the data on mangrove loss reported by Mongabay. The department didn’t respond to questions about how the government will address the loss of mangroves and other riparian trees, Fabro writes.
This is a summary of “For a storm-prone Philippine city, flood control is about more than infrastructure” by Keith Anthony Fabro.
Banner image of Cagayan de Oro flood control project construction, courtesy of Project LUPAD.
This story first appeared on Mongabay
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