By Virginia W. Mason, Kelsey Nowakowski, and Eric Knight

Draining
California

Stretching between the Pacific coast and the Sierra Nevada and Cascades, the Central Valley is the fertile expanse that makes California the U.S. agricultural leader. Going months without rain, the region was transformed into year-round cropland by manipulating the flow of water.

SCROLL TO SEE HOW SNOWMELT FEEDS THE VALLEY

A Fertile Valley

The Sacramento and San Joaquin Valleys form the 450-mile-long Central Valley, which was once an inland sea. Sediment from mountain erosion created its ultrarich soil.

  •  Cropland

Water Source

Gradual spring snowmelt once provided a reliable water supply, collected in dammed lakes and man-made reservoirs. Snowpack water content is calculated each spring by on-site measurement or remote sensor. Most packs are now below normal—69 percent below normal here, at the headwaters of the Rubicon River.

Managing Snowmelt

Lower down on the Rubicon, Hell Hole Reservoir was only 5 percent below normal capacity at the end of February 2014, the result of early snowmelt and precipitation that fell as rain. Reservoirs are kept slightly below capacity, so storm water doesn’t overflow the dam. If levels rise too high, too quickly, water must be released, reducing the amount available in dry summer months.

Diminishing Reserves

On the American River, Folsom Lake reservoir provides water for local communities, crop irrigation, and flood protection for the city of Sacramento downstream. Its bare shoreline reflects three years of drought that have left Folsom at 44 percent below normal capacity.

Groundwater Shortfall

Fed by mountain tributaries, the Sacramento River—California’s largest—carries most of the Central Valley’s water. Wells have typically provided 40 percent of the state’s water. With less water flowing in canals and aqueducts, well use has increased, causing land subsidence, or sinking.

  •  Cropland
  •  Fallow Land
  •  Groundwater Wells
  •  Aqueducts and Canals

Cultivating a Desert

Central Valley cropland and dairy farms produce more than 300 commodities, generating 65 percent of the state’s $42.6 billion agricultural revenue. Up to 20 percent of the cropland is now fallow because of drought and crop rotation.

  •  Cropland
  •  Fallow Land
  •  Groundwater Wells
  •  Aqueducts and Canals

A Man-Made Valley

Every light-blue line or icon on the map is a part of a system engineered to irrigate fields and bring drinking water to much of the state. If drought and warmer winters continue to reduce snowpack and cause earlier melting, meeting the water needs of cities, farms, and wildlife will require difficult decisions.

Reservoir data from end of peak-flow season, as of february 28, 2014. Snowpack data as of april 1, 2014. NOT ALL snowpack-SENSOR sites ARE SHOWN. FALLOW DATA AS OF JULY 11, 2014.

XAQUIN G.V., VIRGINIA W. MASON, KELSEY NOWAKOWSKI, MATT TWOMBLY, JANE VESSELS, AND JASMINE WIGGINS, NGM STAFF. C.Y. Park. CARTOGRAPHIC ART BY ERIC KNIGHT.

SOURCES: california department of water resources; forrest melton, nasa arc-crest; nasa; USGS; USDA; NOAA; bureau of reclamation; National park service; national snow and ice data center; epa; contra costa water district; Westlands Water District; national wildfire coordinating group