![]() ![]() It showed that at rates of relative sea-level rise of 6-9 mm per year, marsh conversion into open water occurs in about 50 years. That research presented an 8,500-year-long sediment record from 355 boreholes in the Mississippi Delta marshes of Louisiana. The results of the June study support the findings of a May 22, 2020, paper in Science Advances, Tipping points of Mississippi Delta marshes due to accelerated sea-level rise. ![]() The situation is more encouraging in Florida: The highest rate of relative sea-level rise at NOAA tide gauges along Florida’s mangrove forests is 3.8 mm per year, in the Florida Keys. About 65% of these sites were able to keep up with this rate of sea-level rise over that relatively short period of time. Global Change Biology 19:1482-1494ĥ.8 mm/yr: New Canal, New Orleans, LouisianaĪ 2017 analysis of wetlands change at 185 sites across the Mississippi Delta found even higher rates of sea-level rise since 2006: 13 ± 9 mm per year. mangrove forests in the southeastern United States. Winter climate change and coastal wetland foundation species: salt marshes vs. Distribution of mangrove forests in the U.S. The NOAA Tides & Currents website indicates that six out of seven coastal tide gauges between Rockport, Texas, and New Orleans, Louisiana, over the past 40 to 50 years had rates of relative sea-level rise exceeding 5.8 mm/year:įigure 2. ![]() Most of the mangroves in those two states are experiencing rates of relative sea level that will threaten their existence. In the U.S., mangroves grow along much of the Florida coast and along large portions of the coasts of Louisiana and Texas. Mangroves in Louisiana and Texas in trouble Credit: Sun et al., Coastal wetlands reduce property damage during tropical cyclones, Proceedings of the National Academy of Sciences Mar 2020, 117 (11) 5719-5725 DOI: 10.1073/pnas.1915169117. The highest-value wetlands were located in the Boston, Massachusetts area. Annual county-level marginal value (the value gained from either consuming or producing one additional unit of a good or service) of coastal wetlands for storm protection in (A) northeastern coastal counties, (B and C) eastern and southeastern coastal counties, and (D) coastal counties from Texas to Florida. Wetland losses of 2.8% in Florida between 19 are estimated to have increased property damage from the 2017 Hurricane Irma by $430 million. Wetlands conferred relatively more protection against weaker storms and in states with weaker building codes. The expected economic value of the protective effects of wetlands varied widely, averaging that $1.8 million per square kilometer. (Side note: a 1% increase in wind increased damages by 7%, and counties on the storm path’s right side experienced 140% more damage than those on the left.) They found that counties with more wetland coverage experienced significantly less property damage: a 1% loss of coastal wetlands was associated with a 0.6% increase in property damage. The researchers analyzed property damage caused by 54 tropical storms and 34 hurricanes hitting the U.S. In the U.S., per square kilometer, wetlands save $1.8 million per year in storm damages.Ī March 17, 2020, study in PNAS, Coastal wetlands reduce property damage during tropical cyclones, showed just how valuable wetlands are in reducing storm damage. ![]() Moreover, wetlands accumulate sediments that provide protection against rising sea levels and local subsidence. At the same time, sediment supply to the coast has declined as a result of damming of rivers and mining and export of sediment, further increasing the vulnerability of mangroves to sea-level rise.Ĭoastal wetlands act as natural levees against storms as a result of their ability to reduce water velocity and wave turbulence. In many coastal areas, the rate of relative sea-level rise is much higher as a result of subsidence resulting from human causes, such as groundwater pumping and fossil fuel extraction.įor example, the Mekong Delta of Vietnam is subsiding at a rate of 6 to 20 mm/year and the Ganges-Brahmaputra Delta by 1 to 7 mm/year. The global rate of sea-level rise has doubled from 1.8 millimeters per year over the 20th century to approximately 3.4 millimeters per year in recent years. ![]()
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