Dams could sustainably feed 1.15 billion people, but as a last resort

Even after being modified with ladders, 'salmon cannons,' and other assistive devices, the dams make it difficult for fish to reach the Pacific Ocean. As a result, three salmon species are endangered or threatened.

Other negative impacts include the depletion of water oxygen levels, which suffocates aquatic animals and plants, sediment build-up, and the displacement of people. Environmental health organizations, such as the World Wildlife Fund (WWF) and International Rivers, support dismantling some dams and developing substitutes.

Stepping up science and innovation to make dams more sustainable

Still, even with these good and bad points about dams in mind, would it be realistic to think that dams are to just go away? Two-thirds of the world's major rivers are already dammed, and this is set to increase.

Additionally, hydroelectric dams supply a renewable energy resource that contributes a huge proportion of the world's renewable energy. Perhaps we only need science and innovation to step up and make them more sustainable.

This is where a recent study by Stanford researchers comes in, which demonstrates that dams could actually help feed the world's eight billion people more sustainably- even if that means as a last resort. They claim that the vast quantities of water storage these structures already provide can be tapped into for maximizing crop irrigation.

Interesting Engineering (IE) spoke with lead scientist Dr. Rafael J. P. Schmitt to discover more.

"Expanding food production would need irrigation, which in many cases would require storage..."

"If we do not deeply rethink agriculture, future food systems would have a major impact on the world's rivers (and would be very expensive). [This is] because expanding food production would need irrigation, which in many cases would require storage," Dr. Rafael J. P. Schmitt told IE.

Common agricultural methods harm natural landscapes, deplete and contaminate water supplies, and are responsible for one-fourth of the world's greenhouse gas emissions.

Two-thirds of all agriculture depends on rainfall. When there isn't sufficient rainfall, like in times of drought, it often makes up for it using non-sustainable water storage sources. These include non-renewable groundwater or obstructing natural flow patterns.

"Storage can be provided by many solutions, but now the largest part of it is from dammed reservoirs"

Some environmentally friendly water storage alternatives for irrigation include recharging groundwater systems with water from winter storms or snow melt in the spring. The utilization of small dams to collect water and better management of field soil moisture are also options.

The team stressed that dams are less desirable for irrigation storage due to water loss, cost, and ecological harm. These tend to be associated with transporting water to far-off agricultural fields. Additionally, dams tend to have higher evaporation rates due to their enormous water surface area.

Yet, realistically speaking, while "storage can be provided by many solutions...now the largest part is from dammed reservoirs," Schmitt said. The team explained that if we could improve methods for storing water in this way, dams could contribute to developing a more sustainable agricultural future.

Hydrothermal dams partly used for irrigation could feed over 600 million people

With this in mind, the researchers examined the amount of freshwater created and replenished by regular hydrological cycles, including groundwater bodies. They also determined the water demands of the current crop mixes on irrigated and rainfed farms.

According to their calculations, storage-fed irrigation of could feed 1.15 billion people at maximum capacity. After analyzing 3,700 prospective hydrothermal dam locations, they concluded that, if partly used for irrigation, dams could feed 641 million people globally.

The Ganges-Brahmaputra basin stood out regarding the potential volume of storage-fed irrigation. Located in the Bengal Delta in Asia, it covers a surface area of some 100 000 square kilometers (km²) and is the world's largest delta. The researchers found that this basin alone could provide food for a total of 189 million people.

Tapping into the power of computer models to analyze real-world data about dams

Schmitt explained to IE, "Our research is mostly based on numerical models. We model for each point on the planet how much sustainable water remains. We then also model how much and when water is needed by crops. The difference between when water is needed and when it is available is what requires storage."

The team also combined global data sets of existing current and future dams to arrive at their figures. "Thus, our research uses computer models to analyze real-world data about dams," he said.

"The analysis of storage needs are also very relevant for energy systems"

"I think the analysis of storage needs are also very relevant for energy systems," Schmitt revealed.

This is due to hydropower being a proven and cost-effective way of storing large amounts of renewable energy, Schmitt explained.

"Another thing that comes to mind concerns agriculture, but not for food: biofuels are also going to need irrigation, and thus also need storage."

"It will not be easy to take away water from hydropower and assign it to irrigation"

While renewable energy sources like wind and solar photovoltaic are growing worldwide, Schmitt highlighted that hydropower is unique. This is because it is the only renewable energy source that can be easily dispatched as it is not reliant on the daily weather. Hydropower will be crucial in helping to decarbonize electrical grids.

Therefore, "It will not be easy to just take away water from hydropower and assign it to irrigation," said Schmitt.

"Building pump storage plants that "recycle" water for energy storage might be an option to keep hydropower benefits for renewable energy grids, while freeing reservoir storage for irrigation," argued Schmitt.

Water issues, however, are local. Thus, more general and worldwide solutions are less effective

Still, the study is not a benefit-cost analysis, as noted by Eric Edwards in a recent article by PopSci. Edwards is an assistant professor at North Carolina State University's Department of Agricultural and Resource Economics.

He explained that water problems are local, so more broad and global solutions are not as effective. "Dams and the related irrigation water distribution infrastructure are very expensive. Often, such projects are not justified based on their improvements in agricultural production and are instead best explained as governmental subsidies to agricultural interests."

How will climate change affect water storage for irrigation?

Despite its limitations, the paper does address a crucial problem with food production. Focusing on irrigation is essential because erratic precipitation patterns brought on by climate change may jeopardize the world's food supply.

"One key next step will be to look into the impacts of climate change and on feedbacks between water storage for agriculture and water storage for energy," said Schmitt.

Still, one cannot help but wonder whether we can really count on dams for their water storage in an unpredictable climate. As this previous article by IE points out, U.S. hydropower plants are in trouble. One example is that climate change-induced drought has already caused water levels to decrease to the point where the dams can no longer generate the same amount of energy.

The bigger picture: "We need a more profound global transformation of agriculture"

"I think the important thing is to realize that we cannot just continue pushing existing agriculture to just grow more food further," he revealed. If we were to expand low-intensity agriculture into natural lands, for example, doing so would significantly affect those terrestrial and river regions.

The authors emphasize that even if large reservoirs are to be built, they will make up only a single part of the solution. They recommend serious evaluation of alternatives instead of creating new dams.

Ultimately, "to grow more food, we need solutions beyond just adding more water to existing croplands. We also need to look beyond large dams to provide storage," Schmitt explained.

"Instead, we need a more profound global transformation of agriculture," he concluded.