Parts of the great San Joaquin Valley are sinking almost 2 inches every month, as the state’s subterranean water supply is being drained to record lows by farms and towns coping with the devastating drought.

On Wednesday, the most comprehensive study yet of the problem revealed the startling pace and extent of the damage: NASA satellites found the ground subsiding almost everywhere in the 140-mile stretch between Modesto and Tulare, with some of the worst sinking near the town of Corcoran, dropping 13 inches, and El Nido, 10 inches, over a six-month period through early this year.

Even worse, the sinking is threatening the stability of the California Aqueduct, as satellite images show a bowl of land between Huron and Kettleman City plunged about 14 inches less than half a mile from the state’s great canal.

“We are pumping more than we are recharging,” Mark Cowin, California Department of Water Resources director, lamented in a Wednesday news briefing to release data collected for the state by NASA’s Jet Propulsion Laboratory. He urged regulation of new wells, saying: “We don’t believe we can sustain this type of pumping.”

Another report released Wednesday warned of the drought’s calamitous impact if California’s historic dryspell continues for another two to three years.

Rural low-income communities, which rely on shallow wells for their water supply, and the environment will suffer the most acute affects, according to a new Public Policy Institute of California study. As many as 18 species of native fish, including salmon, could go extinct, the study found. It also warned of deaths among water birds that use the Pacific Flyway.

In contrast, cities are likely to avoid extreme scarcity, because they’ve invested heavily in conservation, expanded storage, recycled wastewater and other sources, according to the institute’s report.

But the crisis is already well underway in California’s agriculture-rich Central Valley: The intense pumping has left groundwater levels at record lows — up to 100 feet lower than previous records, according to Cowin.

The damage is mounting: Roads have cracked, some pipelines have been exhumed, and the slope of the land is altered, changing drainage patterns, said Jeanine Jones, the department’s deputy drought manager and interstate resources manager.

Along the California Aqueduct, the canal lining has been raised in multiple locations over the years in order to preserve flow.

And the damage to the earth may not be reversible: Even when rains resume, the water cannot expand the underground deep layers of clay, sand and gravel that store the state’s great freshwater aquifers. When pumped too dry, they collapse, stacking like pancakes.

NASA’s satellites can map surface deformations of a fraction of an inch over large areas — making it possible to monitor groundwater and subsidence as never before. The study ended last winter, so does not reflect any additional subsidence caused by summer pumping.

Decades ago, overpumping sunk half of the entire San Joaquin Valley, in one area as much as 28 feet. The subsidence largely stopped when the state and federal governments built reservoirs that delivered water to agriculture.

But with little rain and reduced flow from reservoirs, farmers are turning to aquifers to support their crops. The Central Valley, home to the world’s largest swath of ultra-fertile Class 1 soil, is the backbone of California’s $36.9 billion a year, high-tech agricultural industry.

Some of the areas of greatest subsidence are where agriculture has shifted from grazing and row crops to more intensive cultivation of orchards, such as almonds and grapes, that command a higher profit but demand water to survive year-round. Domestic wells are also failing, because they are shallow and subsidence causes casings to break. In Tulare County, more than 1,500 domestic wells have failed in the past year and a half, and about 1,000 households depend on the county to provide bottled drinking water.

Modesto farmer Paul Wenger blamed the loss of delivered “surface water” from reservoirs for the crisis. Because of the drought, less water is made available to farmers — and more is devoted to fish in the rivers, he said. In 2014, Central Valley farms lost roughly a third of normal surface water supplies, or 6.5 million acre-feet. In 2015, the deficit may rise to 8.7 million acre feet.

Even conservation has unintended effects — drip irrigation, unlike traditional flooding of fields, sends less water back into the ground, he said.

“Farmers have known for a long time about groundwater and subsidence,” said Wenger, president of the California Farm Bureau Federation. “But when I throw you a lifeline, you’ll grab it. You take what you can’t get anywhere else. Farmers are trying to pay bills. They’ll continue to access the only water they have, which is groundwater.”

Last year, the state created a framework to regulate groundwater — the first time in state history — but it won’t be fully implemented until 2020. And then it will take a decade or two for water levels to rebound, Cowin said.

He urged counties to follow the example of Glenn County, which on Tuesday night issued a six-month moratorium on permits for new wells.

“The most important thing that can happen is for counties to pass or strengthen ordinances that limit over-pumping,” he said. “It will take that kind of action to have any real effect.”

Contact Lisa M. Krieger at 650-492-4098. Follow her at www.facebook.com/LisaMKrieger and Twitter.com/lisamkrieger.