California’s agricultural sector has flourished from decades of easy access to water in one of the globe’s biggest swaths of Mediterranean climate. The Sierra Nevada, the spine of mountains that runs along California’s eastern flank, captures an annual cache of snow that, when it melts, cascades into a network of government-built dams, canals and aqueducts that deliver irrigation water to farmers in the adjoining Central Valley. In light-snow years, farmers could tap aquifers that had built up over millennia to offset the shortfall.
But the Sierra snowpack has shown an overall
declining trend for decades – most dramatically during
the great California drought of 2012-2016 – and it will dwindle further over the next several decades as the climate warms, a growing body of research suggests. A
2018 paper by Lawrence Berkeley National Laboratory researchers articulates the alarming consensus: a “future of consistent low-to-no snowpack” for the Sierra Nevada, the irrigation jewel of our vegetable patch.
https://www.theguardian.com/environ...y-to-saving-the-uss-endangered-grasslands-aoe
Even as snowmelt gushing from the mountains dwindles, the Central Valley farming behemoth gets ever more ravenous for irrigation water, switching from annual crops that can be fallowed in dry years to almond and pistachio groves, which require huge upfront investments and need to be watered every year. As a result, farm operations are increasingly resorting to tapping the water beneath them. Between 2002 and 2017, a period including two massive droughts, farmers siphoned
enough water from the valley’s aquifers to fill Louisiana’s Lake Pontchartrain three times.
As the water vanishes, the ground settles and sinks in uneven and unpredictable ways, a phenomenon known as subsidence. By 2017, large sections of the Central Valley were sinking by as much as 2ft a year. In addition to damaging roads, bridges, houses, sewage pipes and pretty much all built infrastructure, subsidence snarls up the canals that carry snowmelt from the Sierra Nevada. Thus we have a vicious circle: reduced snowmelt means less water flowing through government-run irrigation channels, which pushes farmers to pump more water from underground, causing more subsidence that damages those channels and reduces their flow capacity, pushing farmers to accelerate the cycle by pumping more water from underground.