The Upper Colorado River Basin lost more groundwater than the Lower Basin during the severe 2020–2022 drought, a new study finds, challenging assumptions about the resilience of water reserves in the wetter part of the region.
The result matters to farms, utilities and businesses that treat underground water as a fallback when rivers and reservoirs cannot supply enough.
The study, published October 13 in Water Resources Research, estimates groundwater losses of 17.5 cubic kilometers in the Upper Basin and 9.4 cubic kilometers in the Lower Basin during water years 2020–2022. The estimates carry uncertainty ranges of plus or minus 3.5 and 6.5 cubic kilometers, respectively.
Researchers led by Esther Oyedele analyzed satellite and hydrological records for water years 2004–2023. They found different relationships between groundwater and surface-water shortages in the two basins.
A US water year runs from October 1 through September 30 and is named for the year in which it ends.
The paper’s 58.3-cubic-kilometer loss over the full period refers to total terrestrial water storage. Its corresponding groundwater estimate is 25.5 cubic kilometers. Groundwater is only one part of the total.
These regional estimates do not establish how much a particular well can supply, or predict when a company’s water source will fail.
Underground water has physical and financial limits
Groundwater occupies spaces in soil and rock below the surface. An aquifer is a geological formation that stores and transmits it. Recharge occurs when water replenishes that underground supply.
The US Geological Survey’s explanation of groundwater depletion describes the consequences of sustained pumping that lowers water levels. Wells can dry up, water quality can deteriorate, and the cost of pumping can rise.
Water that must be lifted from greater depth requires more energy. Some users may need a deeper well or a different supply. Depletion can also reduce water in streams and lakes and cause land subsidence, the sinking of the ground.
For a business, that creates several separate exposures. A higher energy bill affects operating costs. Replacing a well requires capital. Losing reliable access to water can affect whether production is possible at all.
A farm’s ability to pay for deeper pumping also says little about whether nearby households or smaller operations can afford the same response. Access to equipment does not replenish the shared resource.
Satellites see a regional picture
NASA’s GRACE Follow-On mission tracks changes in Earth’s gravity field to measure the movement of mass, much of it water. It succeeds the original Gravity Recovery and Climate Experiment.
The satellites do not photograph individual underground reservoirs. Changes in their separation help scientists construct gravity maps, which can be combined with other measurements to investigate water storage.
That regional perspective complements local monitoring. A company considering a new plant still needs information about its actual source, permitted withdrawals, seasonal reliability and the infrastructure that delivers water to the site.
In Virginia Tech’s account of the research, hydrologist Susanna Werth calls for managing groundwater and surface water together. The university describes underground reserves as a buffer whose continued depletion can further weaken river flows.
A water plan needs more than a reservoir level
Our earlier reporting on the cost of recycled water for factories examined how treatment requirements and location affect an alternative supply. Businesses can also be exposed through their suppliers.
As a planning exercise, a food processor might examine whether several suppliers depend on the same aquifer, and whether an alternative supplier would face the same drought. Counting contracts alone would not answer that question.
Likewise, a facility with both a river allocation and access to a well should examine how those sources behave during the same dry period. Treating them as independent backups can overstate protection if both deteriorate together.
The October research is a historical assessment, not a forecast of the next drought. Its warning for long-lived investments is that past rainfall and visible reservoir capacity cannot establish the reliability of the water below ground.
