There may be important synergies and trade-offs that cannot be addressed by sectoral strategies and investments alone. For example, growing bioenergy crops in rainfed or irrigated systems may help improve energy supply, but may also result in increased competition for land and water resources with impacts on local food security. Building dams for hydropower may produce energy and provide water storage for irrigation and domestic uses, but may displace people and adversely affect water availability in downstream agroecosystems. These and other similar developments would benefit from greater coordination through a water–food–energy nexus approach to optimize resource-use efficiency.
Many lessons have been learned from the tragic drying up of the Aral Sea in Central Asia, as the water resources were overexploited to grow irrigated cotton. This put excessive pressures on water supplies, creating salinization, pollution from agricultural chemicals and mining wastes on upstream rivers, and loss of aquatic species and fisheries and associated livelihoods.