New research explores how farmers can help California rebuild its groundwater supply
In any given year, agriculture uses the largest fraction of groundwater in the state. But new findings show that empty farm fields could be key in putting that water back underground when storms come through.
In any given year, agriculture uses the largest fraction of groundwater in the state. But new findings show that empty farm fields could be key in putting that water back underground when storms come through.
In any given year, agriculture uses the largest fraction of groundwater in the state. But new findings show that empty farm fields could be key in putting that water back underground when storms come through.
During drought years, California relies heavily on its groundwater supply. As droughts become longer and more intense with climate change, it's becoming more important than ever to "bank" excess surface water during stormy weather patterns in order to provide some long-term insurance.
That's the goal of the Sustainable Groundwater Management Act, which was passed in 2014. In order to meet that goal, state and local water managers need to work together to search for possible methods of recharging groundwater aquifers. And the sooner the better, because there is a lot of water missing from those basins.
"The amount of groundwater overdraft that we have accumulated over the last couple of decades is exceeding 160 million acre-feet, which is about 1.3 times Lake Tahoe," Dr. Helen Dahlke, a hydrology expert at UC Davis, said.
Dahlke and a team of researchers recently shared findings from their study showing how California's 8 million acres of farmland could be tapped as one way to help get water back into the ground through a process called 'Ag-MAR.'
"Ag-MAR stands for agriculture managed aquifer recharge. So managed aquifer recharge is a term we use for intentionally placing more water into groundwater aquifers than would naturally occur from rainfall," Dahlke said.
With Ag-MAR, selected farm fields would be intentionally flooded during periods of stormy weather. Water would then settle into already-existing underground basins below the fields.
With such a huge groundwater deficit to make up and seemingly shrinking opportunities to take advantage of big storms, recruiting help from farmers could create a big opportunity for the state to shore up the water supply for not-so-rainy days.
"We have over 8 million acres in farmland, if you flood just 1 million of that with 2 feet of water or so, you could put a lot of water away," Dahlke said.
But of course, not all 8 million acres of those farm fields would be good candidates for this practice. Crops that are more sensitive to flooding should not be considered.
Dahlke said that the emptying of fallow fields would be ideal because it would minimize the risk of any financial loss for farmers.
Fields with sandy soils would also work better than more clay-based soils because water would be able to drain through much faster.
And when it comes to actually flooding the fields, any farm with a built-in flood irrigation system will be most efficient. Otherwise, flooding would have to take place through sprinklers or drip irrigation, taking much longer.
Scientists also want to learn more about any potential water quality issues with Ag-MAR. Any farm field that uses a nitrogen fertilizer could pass nitrates into the water as it filters through. Those nitrates are known to have health consequences if ingested.
While Ag-MAR is not currently being used in the Central Valley, farmers in the Tulare Basin in Southern California have been trying it out. Each summer, farmers there can register fields for Ag-MAR purposes so the district knows where to send any excess water ahead of time.
There are signs that the practice is working in that area. Dahlke would like to see that eventually expand farther north.
"We have certain targets that we need to achieve so everyone needs to help and Managed Aquifer Recharge is one of those practices that a lot of us can actually implement to reach that goal," Dahlke said.