Emerging Groundwater Issues Likely to Affect U.S. Agriculture

With Skip Hyberg

In August 2023, the New York Times published the results of a study it conducted using a dataset constructed from groundwater monitoring data from the U.S. Geological Survey (USGS) and 28 state and regional water authorities. The report presented two results that highlight the decrease in this important resource.  In 2022, the water level in nearly half of monitored groundwater sites had significantly declined since 1980, revealing that groundwater was being used faster than is sustainable. The second finding emphasizes the consequences of this use, over the last decade nearly 40 percent of the groundwater wells monitored were at their lowest observed level. Most of the declines were found for wells located west of the Mississippi River, with concentrations in the High Plains, California’s Central Valley, and Eastern Arkansas. However, declines were also observed elsewhere including the Atlantic Coastal Plain and Florida. The declining groundwater levels in critical regions, combined with more easily observed lower water levels in surface waters are causing significant problems, such as within the Mississippi River system, where the current drought has recently allowed saltwater intrusion further up the river, and the Colorado River system where reduced flows have triggered mandatory reductions in state water allocations. These matters portend a developing water crisis that requires careful and clear-eyed examination.

Groundwater is a critical national resource. Twenty six percent of all United States water withdrawals, over one third of the volume of drinking water, and 90 percent of US public water systems rely primarily on groundwater. Small public water systems and rural users in particular are dependent of groundwater.  As of 2023, the Environmental Protection Agency (EPA) estimated that 23 million U.S. households rely on private wells for drinking water. In spite of its importance, groundwater use is largely unregulated, and the regulation that exists varies from state to state and across jurisdictions. 

Groundwater exists in many separate independent pools or aquifers across the country, and not all of them are declining. However, the fact that under current regulations groundwater levels are on a long-term decline in many locations and large numbers of people and businesses are dependent on this water leads to the conclusion that something has to change.

Inevitably, that change is going to affect agriculture because agricultural uses account for 68 percent of groundwater withdrawals, with 98 percent of this use being for irrigation. According to the 2018 Irrigation and Water Management Survey (part of the U.S. Census of Agriculture), just under half of the 55.9 million irrigated acres in the United States rely solely on groundwater from wells, while an additional 16 percent utilize a combination of groundwater and surface water. USGS data indicate that groundwater withdrawals increased by 6 percent between 2010 and 2015 and irrigation groundwater withdrawals increased by 16 percent over the same period. The results of the New York Times analysis indicate an unsustainable trend that has implications for agriculture and water use policies. Agriculture needs to recognize these implications and prepare for this change. 
Water issues are complicated involving geologic, climatic, economic, human factors and their interactions. Aquifers are porous underground layers that can store water from precipitation that fell often decades or even millennia ago that has percolated through the ground, and in many cases can take equally long to recharge.  In arid regions groundwater withdrawals can easily exceed the rate that the aquifer is recharged.

Groundwater is stored within the aquifer’s pores and can support the subsurface layer so it does not compress. In some locations the substrate in which the groundwater is stored, can become compacted as water is withdrawn. This compaction can permanently reduce the water storage capacity of that aquifer and its ability to recharge. The subsurface compaction can lead to ground subsidence with economic consequences such as damage to roads, canals, pipes, and other infrastructure. 
Groundwater stored in aquifers often interacts with surface waters, supplying water to maintain base levels for wetlands, lakes, and streams. As ground water levels decrease, these surface waters can shrink or even disappear as they lose their underground water source. Aquifers in coastal zones also interact with ocean water. Over-extraction of groundwater in these areas can lead to salt water intrusion, where ocean water enters the aquifer making the groundwater salty and unfit for most agricultural or human uses.

Climate change is occurring, with most regions facing increased temperatures and more intense precipitation events. As average temperatures increase so does evapotranspiration which both increases demand for irrigation from groundwater sources and reduces the water available for groundwater recharge. In addition, more frequent heavy rainfall events lead to more water running off the surface into waterways which reduces the amount of water available for groundwater recharge.

The economic implications of groundwater depletion for agriculture are formidable. Irrigation has enabled agriculture in many regions to prosper, especially in the western United States, by reducing risk and enabling the production of water intensive crops in arid climates. Declining groundwater levels increase the cost of pumping the water to the surface. And if these levels continue to drop, pumping water for irrigation will become more and more expensive, and in some cases economically infeasible. Additionally, if the level drops far enough the rate of flow from wells decreases, reducing its ability to supply irrigation water. This can increase risk or even force the producer to shift to a less water intensive crop. 

And then there is the human factor. Currently some of the regions with the fastest growing populations, are those with most rapidly falling groundwater levels. These growing populations are increasing demand water and as noted before, groundwater is largely unregulated. These emerging issues provide a strong incentive for agriculture to reexamine water use throughout the United States. It is in agriculture’s interest to help find water use policies designed to balance an increasing water demand with a limited water supply, particularly in the more arid regions with a strong agricultural presence. It is in producers’ interest to understand the implications of different policies so they can be proactive rather than reactive. Our next blog on this topic will examine some of these policy options.