To learn more about how we can cope with drought, nature.org spoke with Senior Freshwater Scientist Eloise Kendy, Ph.D., a hydrologist with The Nature Conservancy for the past six years. She studies groundwater depletion, the movement of water through landscapes, and how conservation can provide solutions to help keep water flowing to farms and cities.
The 2012 U.S. drought was the most severe and widespread in more than two decades, with persistent effects, and has been compared to the great Dust Bowl on the Central Plains in the 1930s. The recent Ken Burns PBS documentary on the Dust Bowl provides a vivid history lesson of how bad things got for Depression-era Oklahoma wheat farmers. Can we learn any lessons from the Dust Bowl experience in how to manage today?
During the 1930s Dust Bowl era, farmers would leave their plowed fields barren for much of the year. When drought came, the soil literally blew off the fields, causing huge dust storms that rendered farming impossible. Where native grasslands had once held soils in place, unsustainable farming practices combined with a prolonged drought to create the Dust Bowl. The disaster eventually led to adoption of better farming practices, such as terracing, use of cover crops, and no-till farming, and creation of the federal Soil Conservation Service (a precursor to the Natural Resources Conservation Service) to promote these practices. As a result, we’ve significantly reduced the rate of soil loss from farm fields.
But the Dust Bowl documentary ends on an ominous note. After suffering through unimaginable consequences of unsustainable farming practices, prairie farmers launched another: pumping groundwater from the Ogallala aquifer for irrigation. Now, as that water source dwindles, the regional economy is again at grave risk.
So, while we learned the most obvious lesson of the Dust Bowl – that is, how to retain soil on dry farmland – we have yet to learn the larger lessons: how to respect nature’s limits, and how to use natural processes to buffer drought’s impacts.
Meanwhile, worldwide we fill wetlands, drain farmland, and replace natural landscapes with impervious roads and buildings. In nature, wetland and forest soils absorb snowmelt and rainfall, slowly releasing it into underlying aquifers and eventually into lakes and rivers. That cool, clean water is what keeps rivers flowing, even when it hasn’t rained for weeks or months. In contrast, drains and impervious surfaces rush rain and snow out of our way, into rivers, and from there to the sea. Draining rain rapidly away when it is plentiful means it’s not here for us to use during drought, when we need it the most.
What kind of agricultural management strategies are working to protect soil and water, and can they be replicated in other places?
Two strategies are to increase the water-holding capacity of soils and, where supplementary water is still needed, to reduce that demand by improving irrigation efficiency.
Improving soil structure not only helps it retain water, but also reduces erosion and protects downstream waterways from pollution and sedimentation. In the Upper Midwest – for example, on the Paw Paw River in Michigan, the Boone River in Iowa, the Pecatonica River in Wisconsin, the Mackinaw River in Illinois, and the Root River in Minnesota – the Conservancy is demonstrating the use of conservation tillage (in which there is little or no turning of soil and crop residue is left to protect soil), as well as contour farming and the planting of cover crops in the off-season, to retain water and sediment on the land. During last summer’s drought, fields where these practices were used had noticeably better crop yields than those that didn’t; in many cases, the improved soil conditions spelled the difference between whether or not a crop was even harvestable. We are working with Congress, the Natural Resources Conservation Service, and the agribusiness community to replicate these and other smart farming practices on all high-risk cropland nationally.
In the Flint River watershed in Georgia, The Nature Conservancy is working with farmers to reduce their demand for irrigation water. With the federal government, we’ve worked to get water-saving technology into the hands of farmers. A team at the University of Georgia invented a new device that allows farmers to use GPS to shut off water to spots in their fields that don’t need it – like wetlands or rocky outcrops. It makes a lot of sense – and saves farmers money – to have these “Variable Rate Irrigation” (VRI) sprinklers all in a line turning on and off, depending on whether the soil is wet or dry. However, whether irrigation efficiency harms or benefits nature depends on the legal and physical circumstances of each unique situation. That’s why Conservancy scientists study all the water pathways to and from a farm before advocating for changes in irrigation practices.
Dams now regulate natural high and low flows in many large rivers. Is drought a problem in places that have reservoirs to store water?
Drought can still be a problem in rivers with reservoirs – just take the Colorado River, dammed to provide hydropower, drinking water to 33 million people, and irrigation for 4 million acres of farmland. The demands are so high, that the Colorado rarely reaches the sea.
Where we have reservoirs, we can operate them better. For recreation, hydropower and water supply, you want to have your reservoir as full as possible. But for flood control, you have to drop the reservoir way down to capture the floods. So, there is a growing view that we can avoid using dams for flood control in the future. Instead we can allow naturally high streamflows to go over the dam where feasible, and allow floodplains downstream to do what they’ve always done - absorb the high flows. This approach keeps more water in the reservoir for cities and farmers to use during droughts. For at least a decade, The Nature Conservancy has been working with the Army Corps of Engineers to manage their dams in this way, through the Sustainable Rivers program.
On the Mokelumne River in California, for example, a study of dam management with the Army Corps demonstrated that relying more on natural floodplains had the potential to free up 25% to 50% of flood storage for “new” storage of public water supply – enough additional water for nearly 450,000 people per year – while increasing hydropower generation and improving habitat for declining salmon.
To realize these benefits would require securing conservation easements on floodplains to replace the flood storage that reservoirs currently provide. But the potential benefits to nature are enormous, as floodplains are among the most biologically productive places on Earth.
The Nature Conservancy talks a lot about managing watersheds, or in other words, rivers and their surrounding lands. How do forests, wetlands and other natural areas act as “green infrastructure” to protect public drinking water supplies?
We’ve learned that nature does a pretty good job of managing water all by itself, and is very complementary to built infrastructure. Natural or green infrastructure includes wetlands, marshes, grasslands and floodplain forests. All of these natural areas absorb high flows and storm water runoff, and filter and slowly release it to streams and aquifers, moderating against dry times. Upslope forests keep rains from flushing out hillsides, and protect water quality by reducing erosion and sedimentation into streams.
While it’s clear people need water infrastructure made of concrete and steel, we’re learning how to better integrate natural services into our man-made systems. Through our conservation planning, the Conservancy identifies important places where green infrastructure can help protect water supplies.
In Texas, the Conservancy worked with citizens to win ballot initiatives for funding conservation easements to protect the groundwater recharge area for the Edwards Aquifer, San Antonio’s primary water source.
In Florida, we’re restoring wetlands on a large scale on agricultural landscapes to improve fish and bird habitat, filter pollution, moderate water temperature and ensure freshwater reaches the Everglades during dry periods while keeping these areas as working cattle ranches.
In Montana’s Centennial Valley, we’re recolonizing beavers because beaver ponds retain spring snowmelt, and slowly release it during the long, hot summer. In other places, scientists report that streams that lack beaver dams run dry in the summer, while otherwise similar streams that have beavers remain perennial.
In Illinois, we are helping the City of Bloomington protect its drinking-water reservoir from agricultural chemicals by assisting farmers to construct wetlands in surrounding farmland. The wetlands remove excess nutrients that come from farm fields and would otherwise contaminate the public water supply.
But these strategies are not one size fits all. The science is really important, because strategies for protecting water resources depend on many factors, such as the geology, soils, and climate, and how the water is used. That's where the Conservancy comes in. We use our conservation science to understand – how nature’s water needs intersect with people’s needs, and can then develop the most effective conservation plan to help keep clean fresh water flowing… especially during droughts.