Global Groundwater and Hetch Hetchy


Groundwater Depletion: Not just a California Thing

Solutions for Restoring Hetch Hetchy Valley Should Be Applied Globally

California's unsustainable reliance on pumping groundwater, especially in droughts, has been well-publicized in recent years. In 2014, the California legislature, after decades of inaction, passed the "Sustainable Groundwater Management Act". 

The SGMA was written to encourage cooperation within local communities (that's the good news), but groundwater basins need not be sustainably managed until 2040 (that's the bad news). 

In an effort to limit the ongoing depletion of aquifers in many parts of California, Senator Lois Wolk has introduced legislation (SB 1317) that would regulate the drilling of new wells.

"This is a serious problem that affects everyone, and it's getting worse," Wolk explains. "Unmitigated, rapid groundwater withdrawals are causing the wells of current homeowners, communities and farmers to go dry. Until we can figure out how to manage this problem and these aquifers sustainably, we need to stop new or deeper drilling in already critically overdrafted water basins."

Groundwater overdraft is not just limited to California - it is a serious problem in many parts of the world. 

Since 2002, the extent of global overdraft has been measured by NASA's Gravity Recovery And Climate Experiment, or GRACE. GRACE continually measures the distance between a pair of twin satellites as they orbit. Small changes in the earth's gravitational field, caused by changes in soil moisture, affect the distance between the satellites.  GRACE's advocate-in-chief, Prof. Jay Famiglietti, appeard on HBO's "Real Time with Bill Maher" in 2015.

In the 15 years that GRACE has been in operation, it has detected long-term changes in groundwater content across the globe. Some areas have become wetter, but many agricultural regions have become drier. See Figure 1. 


Figure 1: Areas with groundwater depletion are shown in dark red, and include California, much of the Middle East, and parts of India and China. Increased moisture is shown in blue.

In some parts of the world, there is little or no water available for recharging aquifers. Water tables are likely to sink lower and lower, increasing the cost of extraction. Even with improvements in efficiency, there simply will not be enough water to sustain populations and agriculture.

But in many places, including California, many aquifers can be recharged in wet or even average years like 2016. In the San Joaquin basin, for example, since mid-March more than 250,000 acre-feet of water supply has been released into the Friant-Kern and Friant-Madera canals for recharge.


The Friant-Kern Canal (Photo: Water Education Foundation)

Agencies in other watersheds do not do as good a job recharging aquifers when water is available. Sometimes it is a matter of geology. But very often, there is insufficient cooperation between landowners and water managers - i.e. no one will recharge an aquifer if anyone can simply pump the water out with impunity. 

It is hard to overstate the importance of managing groundwater - globally or here in California. Doing so is critically important for providing reliable water supply to cities and farms in the decades to come.

Also, as we wrote last fall for the Sacramento Bee, groundwater investment could be a cost-effective solution for restoring Hetch Hetchy Valley in Yosemite National Park.