A study in the journal Science Advances has found that central California is sinking by up to half a meter (1.6 feet) a year due to drought and groundwater loss.
Conducted by Cornell University, the study found that an ongoing drought in the San Joaquin Valley has meant that groundwater hasn’t been replenished, causing the ground to sink.
Farmers extract the groundwater for growing purposes, and have been doing so for more than a century. Usually, this groundwater is replenished by rain and snowmelt, but the drought that began way back in 2011 has prevented this from happening, despite higher-than-normal rainfall last year.
"With the heavy storms in early 2017, Californians were hopeful that the drought was over," Kyle Murray, lead author on the study, said in a statement. "There was a pause in land subsidence over a large area, and even uplift of the land in some areas. But by early summer the subsidence continued at a similar rate we observed during the drought."
The researchers studied satellite imagery of the reason and found that from 1962 to 2011, the average groundwater depletion in the Tulare Basin region in central California each year was 2 cubic kilometers (half a cubic mile). But from 2012 to 2016, they found this had dramatically increased to 42 cubic kilometers (10 cubic miles).
They noted that 86 percent of wells in the Tulare Lake region had reported groundwater levels in spring 2016 that were 1.5 meters (5 feet) lower than in spring 2011. Throughout 2017, this subsidence of groundwater continued.
In California, about 80 percent of groundwater is used for farming. This particular region produces about 250 agricultural products with an estimated annual value of $17 billion, responsible for about 8 percent of the country’s agricultural output.
The loss of groundwater can cause major problems, including forming sinkholes and making roads crack. The sinking ground causes particular problems for the Californian aqueduct system, which relies on the correct slope to carry water.
"Now, one of the major aqueducts in that area is bowed and can't deliver as much water,” said co-author Dr Rowena Lohman. “It's been a huge engineering nightmare."
And if these drought conditions continue, things could get even worse. Dr Lohman noted that the cost of water extraction from groundwater could become so high, coupled with decreasing water quality, that it may no longer be viable to extract it at all.