Fresno Bee Newsroom Blog

Irrigation vapor from Central Valley gives Colorado River big bump

Massive water vapor from farm irrigation in California’s Central Valley each year blows over the Sierra Nevada, pumps up rainfall over other states and adds 100 billion gallons of water to the Colorado River, new research shows.

The Colorado gets nearly a 30% bump in stream flow. That’s enough water to fill nearly two-thirds of Millerton Lake near Fresno.

The study, led by climate hydrologist Jay Famiglietti of the University of California at Irvine,  will be published Tuesday in the journal Geophysical Research Letters. This part of the water cycle has not been accurately described before, Famiglietti said.

If irrigation stopped in the Central Valley, there would be a decrease in the stream flow of the Colorado River basin — a supply of water that has been hotly contested for decades.

The Colorado River basin provides water to Los Angeles, Las Vegas, Phoenix and other cities. Nearly 35 million people, as well as more than 3 million acres of farmland, rely on the water.

The study says more than 12 million acres of farmland are irrigated in the Central Valley, which includes the Sacramento and San Joaquin valleys. As water evaporates into the air, it is caught by the wind and taken over the Sierra.

As it moves into the interior of the Southwest, the vapor feeds into the annual monsoon cycle that includes moisture from the Gulf of Mexico, Famiglietti said.

“Adding the moisture from the Central Valley makes storms wetter and more violent,” he said. “It’s like throwing fuel on a fire.”

He said climate computer models make it possible to isolate the contribution from the Central Valley. The research is an effort to account for as many weather influences as possible.

Famiglietti’s study says about 40% of the irrigation in the Central Valley comes from ground-water pumping, and that worries him.

He wonders what it will mean to the Colorado River If land must be taken out of production as the ground water is depleted.

“It raises questions about the future,” he said.


Mark Grossi says:

Posting for a reader:

Stop and think about the science over a longer time period. Before we tilled the Valley it was a giant wetland much of the time (bulrushes, cottonwoods and willows everywhere). It likely pumped more vapor under those conditions. We probably reduced the vapor stream big time when we dried the ponds up (Tulare Lake, Buena Vista, Goose, Summit, on and on) and did mostly dryland farming in broad areas (big wheat/grain for cattle, see Miller and Lux history). Then wide-scale Valley irrigation came along 100 years later (the water projects finished bringing water to the last of the irrigated areas, Westlands and Kern, in the fifties and sixties of the last century) and added some of the vapor back. Now we are wetting less ground (precision application) and have less surface water so less is getting into the atmosphere. We are also slowly bringing back some wetlands (albeit a drop in the proverbial bucket compared to historical). Everything is in cycles and the information we get and analyze is but a point in time and we never fully grasp the flux of cycles (the Colorado Basin had good years in the early 20th century that set the stage for allegedly unrealistic water allocations when Valley irrigation was still getting started, yet the ponds were gone). Famigletti’s efforts need more context over time to better understand evaporation changes and their impacts.

Sarge Green

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