The case of California’s vanishing groundwater, and a nation’s food security.
In California’s Central Valley, a 47,000 square kilometer area that produces about a quarter of America’s food supply, subsidence is causing the ground to sink anything from a few inches to several feet per year.
It’s not a natural phenomenon that is causing widespread subsidence but rather the region’s agriculture. For decades farmers and agricultural companies have relied on the region’s groundwater to irrigate their crops due to the inadequate supply of surface water for irrigation. The rate of extraction has far exceeded the rate at which the groundwater is being replenished. Coupled with drought due to climate change, the situation has been further exacerbated by shifts in farming practice to crops that are more lucrative for farmers but also far more water-intensive, such as almonds and pistachios. This has increased the rate at which groundwater is extracted and the overall water that is required to sustain the region’s agriculture.
In years of drought, such as in 2014, the rate of groundwater usage is far higher and this has resulted in lower levels of groundwater. The impact of the diminishing supply of groundwater on farmers and people living in the area is massive, with many wells running dry and people having to sink deeper and deeper wells in order to reach the ever-diminishing groundwater supplies. Some simply have to pack up and leave.
Land subsidence results in the lowering of the land-surface elevation due to changes that take place underground. Most of the land subsidence in these areas occurs the first time groundwater is drawn down to a new level. This results in compaction as the water flows from clays in the aquifer. The randomly oriented clay grains realign and organize themselves into a stack as the water is removed which results in less space between and compaction which leads to the ground level above subsiding. This compaction is largely irreversible and further reduces the future overall storage capacity of the aquifers.
Subsidence has further impacted important infrastructure, including roads, bridges, and water conveyance systems. For example, both the California Aqueduct and the Friant-Kern Canal which were designed to augment irrigation capacity and reduce the reliance on groundwater have both been negatively impacted by subsidence. The subsidence has resulted in the canals sinking which has reduced the flow capacity by up to 40%, increased the operational and power costs as well as caused delivery outages. This puts reliable water delivery at risk and leads to increased pumping of groundwater to meet the irrigation needs.
Decreasing water supply and increasing demand put the United States' food security at risk with around 30% of the country’s food supply being grown in the central valley region. Agriculture in this region is worth $17 billion per year to the economy and the loss of this revenue would have an impact on GDP and a catastrophic impact on the region. The sheer scale of this is brought into perspective by the fact that the central valley has less than 1% of the United States’ overall farmland but it has 17% of the nation’s irrigated land and consumes 20% of the entire United States’ groundwater demand.
The enormous demand for water in this region places a serious strain on available water resources with groundwater supplies continuing to decrease year on year. Climate change which has brought about higher temperatures and lower precipitation has further compounded the environmental problem.
During the height of the 2014 drought, thousands of Californians in the Central Valley ran out of water as their wells went dry. The state of California acted and the Sustainable Groundwater Management Act (SGMA) became law. The laws gave local groundwater agencies in critically over-drafted basins until 2040 to achieve sustainability and stop the impact of excessive groundwater pumping from worsening. This action was intended to help prevent future subsidence by stopping the over-pumping of groundwater, however in reality very little has changed and the depletion of groundwater continued. Pumping is largely unrestricted and there are few if any actual protections in place.
The situation is complex, multifaceted, and intricate with many different stakeholders and participants. While there is great awareness, knowledge, and understanding of the issues facing the region, it will require more consistent and intentional actions to improve the chances of identifying and implementing effective ways forward. These solutions need to be inclusive, equitable, and just, particularly for those whose lives and livelihoods would be impacted on.
Politically, there is a need to continue to support, strengthen and enforce important initiatives such as the Sustainable Groundwater Management Act and California’s Healthy Soils Program.
There is a need to look at farming practices and implement shifts in what farmers grow. This could include moving to more drought-tolerant crops, boosting soil health, practicing dry farming, and repurposing land for uses that require less water such as less water-intensive crops, solar arrays, or wildlife habitats.
While there is increased awareness around the issue facing California, and some steps taken to help solve the crisis, a lot more work is required to ensure effective solutions are implemented, sustained, and supported to ensure that the desired positive change occurs in the region.
