The study found that the biggest threat to future water availability for agriculture comes from environmental flow requirements. These requirements ensure that the appropriate water levels needed for a healthy aquatic ecosystem are maintained. But environmental flow requirements, especially when combined with other competition for water resources, can create geographic hotspots of severe water scarcity.
Already, competition for water comes from demands for energy generation and growing urban populations. As water scarcity increases and river-basin supplies are put to full use, more and more water will be diverted from agricultural use. Added to this is the expected growth in population, which will tax water availability and food supply. Furthermore, the growing population is also getting wealthier, meaning more people will demand services that use more water and will shift to diets that consist of water-intensive products. All of this will lead to greater water demand on a per-capita basis, particularly in developing nations.
The MIT study examines three specific factors that may threaten agricultural water availability in the future. The first factor is increased demand for water in municipal and industrial uses, including for domestic and commercial purposes and for use in manufacturing, energy generation or other industrial activities. The increase in water use in these sectors is driven by rising populations and increasing per capita income, but will vary widely across different countries. The exact relationship between per-capita water use and per-capita GDP often depends on the development path of a particular nation.
For example, developing nations such as India and China will likely experience dramatic increases in water use. As per-capita income rises, the way in which people access water will evolve from traditional methods, such as rainwater catchments and public standpipes, to modern services, such as individual household plumbing. Developed countries, on the other hand, may experience a flattening of water consumption with respect to income. As nations like the U.S. and Switzerland introduce water-efficiency measures, per-capita water use may actually decline.
The second factor the MIT study modeled was environmental flow requirements, which regulate a minimum flow of water to allow for the maintenance of aquatic ecosystem services, including considerations for floodplain maintenance, fish migration and water quality. Imposing water flow minimums, while crucial for some ecosystem demands, may cause the demand for water to exceed supply in river basins within the Middle East, central Asia and southern Europe.
The third factor modeled by the study is the impact of climate change on water availability. Climate change can affect the water available for agricultural use through changes in temperature, precipitation and the magnitude and frequency of extreme events. The combination of these climatic impacts will affect the supply of water — in the form of run-off — in different ways around the world. For example, models predict that run-off will increase in eastern equatorial Africa under a warmer climate, while in southern Africa run-off would decline. Rising temperatures will also increase water demands for domestic uses, including garden and lawn watering, thermoelectric cooling in power plants, and electricity generation to meet increased use of air conditioning.
Researchers modeled the effects these three factors would have on agricultural water availability, assuming increased demands were met by the transfer of water currently used for agriculture. The study found that meeting environmental flow requirements presents the biggest threat to agricultural water availability, with the second-largest threat coming from increased municipal and industrial demands.
In areas with growing populations and income, water demands are projected to increase by more than 200 percent by 2050. When combined, increases in demand for water from municipal and industrial uses and environmental flow requirements cause an 18-percent reduction in the water available for agriculture globally.
Climate change alters the distribution of water supply. Therefore, climate change can increase the threat to agriculture in some areas, such as Africa, Latin America and the Caribbean, and decrease the threat in others, such as North America and Asia.
The effect of competition for water creates dramatic geographical hotspots where water resources available for agricultural purposes are threatened. Such hotspots include northern Africa, India, China, parts of Europe, the western U.S., and eastern Australia — areas that already tend to experience water scarcity. Competition for water may pose significant threats to future food systems in these regions.