66 CONVENIENT SOLUTIONS TO AN INCONVENIENT TRUTH
TABLE 3.1
Ecosystem-Based Approaches to Defend against Natural Disasters Natural Hazard Types of Ecological Protection
Examples
Flood
Dense vegetation cover within upper watershed areas increases infiltration of rainfall and reduces surface runoff, reducing peak flow rates except when soils are fully saturated. Vegetation also protects against erosion, reducing soil loss and transport of mud and rock, which greatly increases the destructive power of floodwaters.
Hurricane Jeanne hit several Caribbean islands, but the number of flood-related deaths was more than 3,000 in Haiti compared with a few dozen in all other affected countries, due in large part to Haiti’s highly degraded and flood-responsive watersheds. The pattern of economic losses was similar during the 2008 hurricane season, although the loss of life was far lower.
Dense vegetation protects riverbanks and adjacent land and structures from erosion by floodwaters.
A study around Mantadia National Park, Madagascar, concluded that conversion from primary forest to swidden can increase downstream storm flow by as much as 4.5 times.
Tsunami, storm surge
Wetlands and floodplain soils absorb water, reducing peak flow rates downstream.
Communities have planted bamboo to protect channel embankments from annual floods in Assam. Canalization and drainage in the Mississippi floodplain reduced flood storage capacity by 80 percent and have been linked to subsidence of large areas and the severity of the impact from Hurricane Katrina.
Coral reefs and sand dunes (which in coastal areas typically depend on associated plant communities for maintenance) provide a physical barrier against waves and currents.
Modeling for the Seychelles suggests that wave energy has doubled partially as a result of changes in the structure (due to bleaching) and species composition of coral reefs. In the Caribbean, more than 15,000 kilometers of shoreline could experience a 10–20 percent reduction in protection from waves and storms by 2050 as a result of reef degradation.
Salt marshes and lagoons can divert and contain floodwaters.
Re-establishment of salt marshes forms part of coastal defense measures in the United Kingdom.
Mangroves and other coastal forests can absorb wave energy and trap floating debris, reducing the destructive power of waves.
Data from two villages in Sri Lanka that were hit by the devastating Asian tsunami in 2004 show that, while two people died in the settlement with dense mangrove and scrub forest, up to 6,000 people died in the village without similar vegetation. In Japan, where good historical records exist, the role of forests in limiting the effects of tsunami damage have been demonstrated. (continued)