Race to the Bottom: An Overview of California’s Groundwater Overdraft Crisis

As the ninth highest user of groundwater worldwide, California now finds itself in a groundwater overdraft crisis. Pumping more groundwater than any other U.S. state, California extracts 14.2 million acre-feet of groundwater on average each year.

Groundwater is a critical resource for California. More than 80% of Californians rely on groundwater for daily needs, and competition for the usage of this resource spans many industries. California’s Central Valley produces a quarter of the United States’ food, making agriculture an especially large driver of groundwater extraction in the state. Despite groundwater's obvious importance to people and industries, competing needs have led to poor management of the resource in California and have resulted in alarming environmental impacts.

Groundwater and Surface Water

So what is groundwater anyway? Groundwater is the water found underground in the cracks and spaces in soil, sand, and rock. As the largest source of usable freshwater in the world, groundwater provides drinking water for 51% of the total U.S. population. This number jumps to 99% when we examine drinking water sources for rural populations across the country. Surface water, on the other hand, encompasses any body of water found above ground. That includes rivers, wetlands, reservoirs, creeks, streams, and, despite being salt water, the ocean.

Groundwater and surface water are hydrologically connected, and this connection has profound implications for sustainable resource management. Within a hydrologically connected region, an equilibrium exists between groundwater and surface water. Disruptions to that equilibrium, such as groundwater pumping, negatively impact not only the groundwater supply but also have a cascading effect on surface water and associated ecosystems. When groundwater is overused, the lakes, streams, and rivers connected to groundwater can also have their supply diminished.

However, despite this hydrological connection, surface water and groundwater were historically treated as entirely separate resources in California and, as such, were governed under a completely different set of rules. Up until 2014, when the Sustainable Groundwater Management Act (SGMA) passed, groundwater usage was largely unregulated, while regulations surrounding the use of surface water have been in effect for quite some time. By overlooking the important interaction between groundwater and surface water, California repeatedly made decisions about groundwater extractions that generally failed to address the resulting impact to surface flows and aquatic ecosystems.

Issues Surrounding Groundwater

Due to heavy resource competition and the reliance California has on groundwater supplies, California is experiencing the effects of groundwater overdraft. Groundwater overdraft occurs when the amount of water withdrawn exceeds the amount that recharges the basin. In California, 21 out of 515 groundwater basins are considered to be critically overdrafted.

Groundwater overdraft can hold social consequences. In some parts of the state, water tables have dropped 50 feet or more in just a few years. As a result, many domestic wells in rural areas are drying up, meaning entire communities are experiencing water deprivation. Another consequence of overdraft is land subsidence, a process that causes the land surface to sink and often results in damage to infrastructure such as roads and bridges.

The over-extraction of groundwater can also lead to several ecological consequences. Basins with decreased groundwater levels replenish by drawing in water from adjacent water systems, which can reduce the critical water levels needed for ecosystems and habitat. California’s groundwater dependent ecosystems tend to take the brunt of this interaction.

Groundwater Dependent Ecosystems

Groundwater dependent ecosystems (GDEs) are plant and animal communities that require access to groundwater to meet some or all of their water requirements. This is known as a direct reliance on groundwater. Species that directly rely on groundwater include fish such as Chinook salmon that use streams for spawning, and phreatophytes that uptake groundwater through their roots. A species can also indirectly rely on groundwater, meaning that groundwater supports their forage and habitat requirements. Species with an indirect reliance on groundwater include riparian birds, such as the Willow Flycatcher, which rely on groundwater dependent vegetation. Reliance on groundwater can also vary over time or depending on location.

Groundwater Dependent Ecosystems provide an immense amount of value through various functions; GDEs supply water and base flow in rivers, reduce flood risk, and purify water. In California, wetland ecosystems are disappearing due to the consequences of groundwater overdraft. This holds implications for the endangered plant and animal species supported by the GDEs as well as the environmental processes they facilitate.

Foundry Spatial California Water Framework

There exists a lack of data and tools in California to prevent adverse impacts to groundwater, surface water, and their dependent ecosystems. In light of this, the state has reached a critical junction where leading-edge solutions are vital for the long term sustainability of these resources. By unlocking the mystery of how groundwater is connected to surface water, the Foundry Spatial California Water Framework is helping resource managers and decision-makers understand the past, present and future surface water depletion that results from groundwater pumping. Our objective with the development of the Foundry Spatial California Water Framework is to address the imminent need for data and tools in California by providing accessible, actionable information concerning sustainable groundwater management in the state.


Critical Species LookBook
Queensland DES Wetland Info | Groundwater Dependent Ecosystems
Groundwater Foundation | Groundwater Basics
Groundwater Resource Hub | What are GDEs?
National Geographic Encyclopedia | Surface Water
PPIC | Groundwater in California