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Wetlands Do Triple Duty in a Changing Climate

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Miss River Floods May MO TN NASA
Mississippi River flooding in Missouri and Tennessee, May 2011. (Photograph by NASA)

This year’s heavy, widespread snowfall across the interior U.S. has people watching flood forecasts for the Mississippi River Basin closely, as the ground thaws and thunderstorm season cranks up. This is understandable, as three memorable “100 year” floods struck the Mississippi River Basin in 17 years—in 1993, 2008, and 2011—with more local flooding in between.

While this year’s Mississippi River flood forecast appears moderate, planting season is a good time to reflect on recent history and take stock of future flood and drought projections.

Massive flooding of historic proportions swept through Cedar Rapids, Iowa in June 2008. The economic damages were so high—$5-6 billion—that some vocal critics argued against re-building in the floodplain.

More flooding inundated the Mississippi River system a few years later. Following heavy rains and snowmelt, floodwaters crested at 48 feet in Memphis, Tennessee in May 2011, just below record flood stage. Thousands of homes were evacuated there and in Louisiana and Mississippi.

Fast forward to summer 2012, when crop-withering drought parched nearly two-thirds of the contiguous United States, devastating farms across the Corn Belt. That year, two-thirds of farmers polled across the Midwest told Iowa State University researchers that they believe the climate is changing, and drought was their number one climate concern. While massive flooding is an urban nightmare for river cities, drought can be one of the scariest things for farmers, according to J. Gordon Arbuckle, Jr., who conducted the poll.

Drought parched much of the contiguous U.S. in 2012. (Photograph by USDA)

Climate Change Brings Increased Risk of Major Floods and Drought

The recently released Intergovernmental Panel on Climate Change (IPCC) report “Climate Change 2014: Impacts, Adaptation, and Vulnerability” details the growing long-term risk of drought and floods as a result of precipitation extremes and heat waves. Climate scientists predict a double whammy of heavy, prolonged spring downpours with widespread flooding and more summer/fall heat waves and droughts for interior North America. The IPCC report also predicts the breakdown of global food systems linked to warming, drought, flooding, and extreme and variable precipitation.

Such wet and dry extremes in the same region might seem like a baffling contradiction, but they are actually “opposite sides of the same coin,” according to Eileen McLellan, Senior Scientist at Environmental Defense Fund. Climate impacts of flood and drought are both exacerbated by the historic and ongoing loss of wetlands and floodplain function across the Corn Belt, Dr. McLellan contends.

At least 35 million acres of wetlands have been filled and plowed under in the Upper Mississippi River Basin and, unfortunately, that number continues to grow to the present day. When allowed to do their jobs, wetlands and floodplains capture and store precipitation and storm run-off, thereby providing flood protection for cities and farms downstream.

Wetlands, in many cases, also act as natural reservoirs that re-charge the subterranean water table, providing another form of drought insurance for ecosystems and groundwater users.

Climate change will have serious consequences for farms, cities, fish and wildlife in our lifetimes, unless we dramatically transform the way wetlands are managed in agricultural landscapes.

Wetlands Store Floodwaters and Carbon

According to the U.S. Environmental Protection Agency (EPA), bottomland hardwood-riparian wetlands along the Mississippi River used to store 60 days of floodwaters but now, because of draining and filling, they only have the capacity to store 12 days of floodwaters.

As living systems that support dense plant life, wetlands not only capture polluted stormwater, they also capture and store carbon (a potent greenhouse gas that contributes to climate change), potentially slowing the rate of global warming.

Wetlands Sustain Vulnerable Fish and Wildlife

Furthermore, the habitat benefits of wetland restoration are potentially enormous. Species that depend on shallow water habitats that are subject to drying, like wetlands, are the most highly vulnerable to climate change in drought-prone regions of the U.S. In Iowa, constructed wetlands have been providing breeding habitat for trumpeter swans.

Wetlands can therefore do triple duty to reduce climate change impacts—storing floodwaters, capturing carbon, and sustaining biodiversity. Restoration of natural infrastructure like freshwater wetlands should become a key piece of our national climate change adaptation strategy.

A trumpeter swan brood in a wetland habitat. (Photograph by Donna Dewhurst, U.S. Fish & Wildlife Service)
A trumpeter swan brood in a wetland habitat. (Photograph by Donna Dewhurst, U.S. Fish & Wildlife Service)

Wetlands Improve Water Quality

Along with heavy spring downpours and runoff from agricultural fields comes impaired water quality. The IPCC projects that climate change will reduce water quality and pose risks to drinking water even with conventional treatment, due to interacting factors of increased temperature; increased sediment; fertilizer-polluted runoff from heavy rainfall; increased concentration of pollutants during droughts; and disruption of treatment facilities during floods.

Their recent report suggests that conservation of wetlands and more “green infrastructure” to capture surface run-off can reduce the intensity of flood events and improve water quality. This makes a strong case for re-establishing networks of wetlands across the interior U.S.

Freshwater wetlands upstream can improve water quality by capturing and filtering fertilizer pollution before it makes its way into rivers and eventually the Gulf of Mexico, where it contributes to growing oxygen-depleted “dead zones” otherwise known as “hypoxia.”

In the Corn Belt, nitrogen runoff from crop fields is the main cause of Gulf hypoxia many miles downstream. The EPA has called for a 45 percent reduction in nitrogen inputs to waterways. But the increased storm runoff that will come with climate change will also likely increase nitrogen going into waterways, so we may need something more like a 60-70 percent reduction to significantly reduce hypoxia, Dr. McLellan estimates. How we will achieve that is a huge challenge, but wetlands are a key solution.

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Gulf of Mexico hypoxia zone. (Image by NOAA)
Boundaries and names shown do not necessarily reflect the map policy of the National Geographic Society.

Climate Change Threatens Global Food Security

The IPCC also reports a slow-down in the growth rate of global agricultural productivity, linked to climate change. They report that climate change threatens food security globally, particularly for poorer populations in urban and rural settings.

This means lost rural livelihoods and income due to insufficient access to drinking and irrigation water and reduced agricultural productivity, particularly for poor farmers and pastoralists in semi-arid regions of the world.

It also likely means increasing demand for U.S. agricultural exports in the future and growing pressure on land and water resources, just at a time North American ecosystems are becoming more stressed, intensifying the challenge of keeping natural systems working and intact.

How will we continue to provision the world while shrinking our footprint on the landscape? Wetlands, with a relatively small footprint, provide a powerful climate change resilience strategy as natural infrastructure that can buffer society, agriculture, and natural ecosystems against the most extreme weather impacts, like drought, flooding and water pollution.

Wetlands Increase Climate Change Resilience

The greatest opportunities for increasing resilience to climate extremes in the U.S. Corn Belt region right now are in the agricultural part of the landscape. By reducing tillage of the soil, maintaining and restoring wetlands, we can store more water in the soil, in the water table and on the landscape, meaning less polluted water rushing downstream to create floods and dead zones, and more stored groundwater to protect terrestrial plants against drought.

One definition of agricultural sustainability in a changing climate could be helping to meet the food needs of a growing population in ways that benefit, rather than harm, the environment. Part of the solution to climate impacts in the interior U.S. will be improving how we manage water on the landscape. This means demonstrating the value of wetland-related practices to improve water quality and reduce floods, while simultaneously increasing the resilience of farm operations to extreme weather events.