A bogeyman for many environmentalists, dams could actually play an important role in feeding the world in a more sustainable way, according to a new study from Stanford University. The study, published the week of November 14 in PNAS, quantifies for the first time how much water is needed to maximize crop irrigation without depleting water stocks or encroaching on nature, and how many people this approach could feed. While the researchers find that dam reservoirs could be used to store more than 50% of the water needed for such irrigation, they point out that large reservoirs are only part of the solution and recommend evaluating alternatives to building new dams because of their adverse effects on the river. ecosystems.
“There is an urgent need to explore alternative water storage solutions, but we must recognize that many dams are already in place,” said study lead author Rafael Schmitt, a research engineer at Stanford. Natural Capital Project. “Our research sheds light on their crucial role in ensuring food security in the future.”
Typical agricultural practices in many parts of the world deplete and pollute water resources, damage natural landscapes and together generate a quarter of global greenhouse gas emissions. Two-thirds of the world’s cropland depends on rainfall and often compensates for its lack by using unsustainable water resources, such as non-renewable groundwater, or by impeding environmental flows.
Potential of sustainable irrigation
Researchers analyzed the amount of freshwater in surface and groundwater bodies generated and replenished by natural hydrological cycles, as well as the water demands of current cropping mixes on irrigated and rainfed lands. They estimated that the full potential of storage-fed irrigation could feed about 1.15 billion people. If the 3,700 potential dam sites that have been mapped for their hydropower potential were built and partially used for irrigation, the world’s dams could provide enough water to irrigate the crops of about 641 million people, or 55 % of total.
Despite the potential of dams, researchers caution against relying on them as an important part of the sustainable irrigation solution, citing the socio-environmental consequences of dams, such as the fragmentation of rivers, with impacts on fish migration and sediment transport, and movement of people. Dams are also less attractive for irrigation storage due to the loss of water, expense, and ecological damage associated with the need for transportation to distant agricultural fields, as well as higher levels of evaporation on dams. large water surfaces of large reservoirs.
“Of all supply and demand side options to increase food and water security, building more dams should be the last resort,” the researchers write.
Alternative solutions to provide more environmentally friendly water storage for irrigation include water harvesting with small dams, recharging groundwater systems with excess surface water from winter storms or spring snowmelt, and better soil moisture management in agricultural fields. These decentralized approaches lose less water to evaporation, require less transportation infrastructure, and often create co-benefits for local communities and wildlife.
Additionally, the researchers point out that the demand for stored water can be reduced through better irrigation techniques or the adoption of crops better suited to water availability. With storage being such a bottleneck for future agriculture, better land management that reduces erosion – and therefore sedimentation and storage loss – in existing reservoirs is an additional priority.
“Nutrition security is a major challenge for sustainable human development,” said study lead author Gretchen Daily, co-founder and faculty director of the Stanford Natural Capital Project. “Our study highlights the urgent need and opportunity for nature-positive investments in irrigation and water management to reduce the harmful impacts of agriculture while supporting other vital benefits of agricultural land and freshwater ecosystems.”
Daily is also the Bing Professor of Environmental Science at Stanford School of Humanitiesand principal researcher at Stanford Woods Institute for the Environment.
The research was funded by the Wallenberg Foundation.