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Climate Change and Wetlands: Severe Storms

Recent evidence reveals that increasing temperatures are not only altering precipitation patterns, they are also boosting storm intensity. Scientists at the University of Wisconsin-Madison and the National Climatic Data Center of the National Oceanic and Atmospheric Administration report that a warming climate is to blame for an increasing number of severe hurricanes in the Atlantic over the past 15 to 20 years. According to the Institute of Global Environment and Society, the United States has seen a much higher than normal occurrence of storms with large precipitation amounts since 1970. Additionally, an increasing amount of precipitation falling in the U.S. is coming from severe storms.

Two factors that contribute to more intense storms—warmer ocean waters and water vapor—have both increased over the past several decades. The oceans are absorbing 20 times more heat than the atmosphere, which is causing water temperatures to rise. This warmer water is pumping more energy into hurricanes and cyclones, fueling their growth into bigger, more intense storms. Warmer air temperatures are also increasing evaporation rates, which means that a greater amount of water vapor is available to feed the storms’ growth. Research has shown that while overall hurricane frequency has not changed much over the past 30 years, the number of Category 4 and 5 storms has increased dramatically. As these storm systems get bigger and more violent, they can cause serious damage to coastal wetlands. Healthy coastal wetlands are extremely resilient and can protect inland ecosystems and communities from severe weather. However, many of our coastal wetlands have been weakened by development. Human-constructed ditches, dams, and levees prevent new sediment from traveling downstream and accumulating in coastal marshes, estuaries, and river deltas. The result is that storm surges and extreme weather are eroding these wetlands faster than sediment deposits can rebuild them.

Severe storms damage forested wetland habitat by killing and preventing the growth of large canopy trees, leaving only shrubs and small trees intact. This not only destroys habitat for many wildlife species, it also leaves the wetlands increasingly vulnerable to wind and wave erosion. In 1992, Hurricane Andrew caused severe damage to the forested wetlands of Atchafalaya Basin, which contains a third of the remaining bottomland hardwood forest and swamp forests of the lower Mississippi floodplain. Not only were many trees killed or damaged by the strong gusts of wind, the massive amount of fallen leaves and organic debris in the swamp caused a severe drop in dissolved oxygen levels and a large die-off of fish. Greater storm intensity also increases stormwater runoff, which introduces more pollutants into our wetlands and waterways. The fewer wetlands there are to filter these pollutants, the more polluted our groundwater becomes.

A well-established and healthy network of wetlands is also a crucial frontline of defense protecting our coastlines from storm surges and hurricanes. By acting as a barrier to storm surges, breaking up large waves, and absorbing floodwaters, wetlands help protect coastal communities and neighboring ecosystems from these natural disasters. According to the U.S. Geological Survey, it can take as little as one mile of healthy wetland to reduce storm surges by one foot. The aftermath of Hurricanes Katrina and Rita leaves no doubt about the link between wetland loss and storm damage. According to the Louisiana State University Hurricane Center, the two storms were more destructive in places where wetlands had been extensively damaged or destroyed.

Fortunately, the federal government and other authorities have acknowledged the importance of healthy wetlands and are funding projects to help protect, create, and restore wetland habitat. In 2006, the Orange County Water District in southern California was awarded $2.85 million as part of a grant from the Federal Emergency Management Agency to help repair and restore the Prado Wetlands, which had been damaged by the previous year’s severe storms. The 465-acre Prado Wetlands are a series of 50 shallow ponds that were constructed to help purify the Santa Ana River, which then replenishes the groundwater supply for Orange County. Severe storms during the 2004-2005 winter season resulted in extremely high water levels, which flooded the Santa Ana and filled the wetlands with sediment and debris. Today, however, the wetlands are back to health and providing habitat for a multitude of wildlife—including bobcats, frogs, red-tailed hawks, great egrets, ducks, and the threatened least Bell’s vireo.

Critter Corner
Weathering the stormy seas: Mangroves

What happens when the coastal marsh meets the steamy tropics? There is only one place in the continental U.S. where this happens, and that is along the extreme southern edges of Florida. Here, the prairie-like expanses of Spartina grasses found in coastal marshes up north give way to an impenetrable tangle of vines, woody vegetation, and a curious tree called the mangrove. Despite the fact that mangrove swamps are recognized to be highly valuable to both our economy and the environment, these ecosystems are among the most threatened in the nation. Coastal development is the leading cause of mangrove destruction in Florida. This loss has devastating consequences not only for the resident wildlife, but also for nearby human communities that rely upon these natural barriers to protect them from flooding and erosion. Climate change may cause these threatened wetlands to become even more scarce.

One of the mangrove’s most recognizable characteristics is the way it stands above the water on its stilt-like roots. These roots not only provide a support structure, they allow the mangrove to take in the oxygen and nutrients that are only found in the uppermost layers of soil. Because of the large amounts of nutrients cycled through mangrove swamps, the productivity of these ecosystems is often compared to that of rainforests and coral reefs. What’s more, 80 percent of the fish and shellfish harvested in Florida rely upon the maze of prop roots that lies beneath the surface of a mangrove swamp at some point during their life cycle. Mangrove forests provide an abundant source of food, hiding spots, and calm waters not only for young fish, but also the endangered manatee. Additionally, these unique ecosystems serve as a vital buffer against the wind and wave action generated by hurricanes and other severe storms.

As global warming continues to boost the number of severe storms, mangrove ecosystems are increasingly being confronted with more than they can handle. In 1960, Hurricane Donna devastated more than 100,000 acres of mangrove swampland in southern Florida. In some areas, tree loss reached 100 percent as trunks were sheared, prop roots buried, and entire islands drowned. Sea level rise is another effect of global warming that could have dire consequences for mangroves. Although mangrove swamps can migrate inland as water level rises, in many places they would encounter housing developments and other manmade barriers that would prevent new swamps from becoming established. Additionally, some fear that sea levels may rise so fast that there would not be enough time for mangrove forests to re-establish themselves farther inland. According to a report by the National Wildlife Federation, the water level in Tampa Bay could rise 15 inches in the next 100 years. This would be devastating to many coastal wetlands, including mangrove swamps.

Fortunately, Floridians recognize the value of their mangrove wetlands, and regulations have been enacted to protect them from development. Mangroves cannot be removed, pruned, or disturbed on either state or private land without a permit from the Florida Department of Environmental Protection. Additionally, several programs have been established to help protect and restore endangered wetland habitat. One example is the Tampa Bay Estuary Program. Established in 1991, this program aims to educate citizens about the threats to Tampa Bay’s coastal wetlands, and to help restore degraded wetlands to health. Florida is also taking some of the steps needed to prevent the most severe effects of global warming. In July 2007, Florida’s Governor Charlie Crist signed three executive orders designed to reduce the state’s contribution to global warming pollution. Additionally, Miami-Dade County has implemented a plan to help reduce greenhouse gas emissions. As awareness of the consequences of global warming grows in Florida and the rest of the nation, initiatives like these are becoming more commonplace. This is good news for mangroves and millions of other wetland-dependent species, whose continued survival depends on our ability to stop global warming.

VOLUME FOUR
Issue No. 5