Large-scale agriculture in the Southwestern United States, including states like California and Arizona, operates in a naturally water-scarce environment. This region’s arid or semi-arid climate, with low precipitation and high temperatures, makes farming reliant on extensive irrigation. This reliance creates a fundamental tension between agricultural production and the sustainability of limited water resources. The agricultural sector’s demand for water places considerable strain on the region’s supply systems, shaping water availability for all users.
Key Water Resources Under Pressure
The agricultural sector in the Southwest draws upon a finite set of water resources. A primary source is surface water, dominated by the Colorado River. This river is a lifeline for the region, supplying water to seven states and Mexico, with its reservoirs, Lake Mead and Lake Powell, serving as the largest storage systems. Agriculture in states like southern California depends heavily on allocations from this river.
Beyond rivers, the industry relies on vast underground reserves known as aquifers. In California, aquifers in the Central Valley are fundamental to the state’s agricultural output, while parts of New Mexico utilize the Ogallala Aquifer. Since the mid-20th century, groundwater has consistently supplied at least one-third of the water demand for agriculture across the Southwest.
To move water across vast distances, elaborate conveyance systems are also used. The Central Arizona Project is a 336-mile-long aqueduct that diverts water from the Colorado River to serve central and southern Arizona for both urban and agricultural needs. Similarly, California’s State Water Project transports water from the northern part of the state to agricultural areas in the south.
Agricultural Water Demand and Consumption
Agriculture is the single largest user of water in the Southwestern United States, accounting for roughly 80% of all water withdrawals. This demand is driven by the cultivation of crops that, while economically valuable, require substantial irrigation. Water-intensive crops like alfalfa, cotton, and almonds are widespread throughout the region. In Arizona, the cultivated area for alfalfa, a thirsty forage crop used for cattle feed, increased significantly between the mid-1990s and 2022.
The methods used to irrigate these crops contribute to high water consumption rates. Traditional practices such as flood irrigation, where water flows over fields, are still in use but can result in significant water loss through evaporation and runoff. While modern methods like drip irrigation deliver water more directly to plant roots and are more efficient, their adoption is not universal. The economic incentives to grow high-yield crops often outweigh the pressure to conserve water, perpetuating a cycle of high demand.
Depletion and Scarcity of Water Supplies
The thirst of large-scale agriculture has led to the measurable depletion of the Southwest’s water resources. The Colorado River has experienced such significant diversions that its flow has diminished, often preventing it from reaching its natural delta. This reduction is mirrored in the shrinking levels of its primary reservoirs, Lake Mead and Lake Powell, which have fallen to historic lows in recent years, signaling an imbalance between water supply and demand.
Groundwater resources are being depleted at an unsustainable rate through aquifer overdraft, where more water is pumped out than is replenished. In California’s San Joaquin Valley, extensive pumping for agriculture has caused groundwater levels to fall, leading to wells running dry and the ground surface to sink, a phenomenon called land subsidence. Since 2010, increased irrigation in New Mexico’s Mimbres Basin has similarly accelerated groundwater declines, prompting new regulations.
This depletion of both surface and groundwater creates widespread water scarcity. The shrinking supply intensifies competition among users, pitting agricultural interests against the needs of growing urban populations and the environment. As water becomes scarcer, conflicts over allocation rights become more frequent and contentious, forcing communities to consider difficult trade-offs between economic activity and water security.
Degradation of Water Quality
Beyond diminishing the quantity of available water, large-scale agricultural practices also degrade the quality of remaining supplies. Agricultural runoff is a primary vehicle for pollution, carrying contaminants from fields into rivers, streams, and aquifers. This runoff frequently contains excess nutrients from fertilizers, such as nitrates and phosphates. When these nutrients enter water bodies, they can trigger algal blooms that deplete oxygen and harm aquatic life.
Pesticides and herbicides applied to crops also find their way into water systems through runoff. These chemicals are designed to be toxic to pests and weeds but can also be harmful to other organisms, including fish and wildlife, if they contaminate drinking water sources. The presence of these pollutants can make water treatment more complex and costly for downstream communities.
A more subtle issue is the increasing salinity of water and soil. In arid regions, irrigation water contains dissolved salts that are left behind in the soil after water evaporates. Over time, these salts accumulate, degrading soil health and making it harder to grow crops. Excess irrigation water that drains back into rivers or aquifers carries these concentrated salts, increasing the salinity of the water source for all downstream users.