The water cycle and water insecurity

Figure 1: The Colorado River supplies water to about 40 million people in seven US states and Mexico, and irrigates around 2 million hectares of farmland. About 70–80% of the water used goes to agriculture. Figure 2: Water allocations under the 1922 Colorado River Compact were based on unusually wet years. Average flow in the 20th century was around 18 billion m³ per year; since 2000 it has averaged closer to 15 billion m³. Figure 3: Lake Mead, the largest reservoir, fell to about 27% of capacity in 2022. Federal shortage declarations led to cuts for Arizona and Nevada. Figure 4: Stakeholder views: • A farmer in Imperial Valley: 'We hold the oldest rights. Our alfalfa feeds cattle across the country.' • A Las Vegas water manager: 'We've cut our use per person by nearly half since 2002 with turf removal and recycling.' • A Native American tribal leader: 'Many of our homes still lack running water, though our rights are among the most senior in the basin.' • A Mexican environmental scientist: 'The river rarely reaches the sea. The delta wetlands have nearly disappeared.' Figure 5: Climate projections suggest a further 10–30% decline in flow by 2050 due to higher temperatures increasing evaporation and reducing snowpack.