Posted on 02/02/2013 11:15:45 PM PST by neverdem
Water diverted to central California's farmlands boosts rainfall in nearby states and may even exacerbate periodic flooding in some regions, a new study suggests. The phenomenon may also be happening elsewhere in the world.
California's Central Valley—an area almost twice the size of Massachusetts where farmers raise more than 200 different crops, including apricots, asparagus, cotton, and grapes—is one of the largest irrigated regions in the world. Every year, several cubic kilometers of water are supplied to the Central Valley's fields, about 60% of it from river flow diverted into the region and the rest from wells. A significant amount of that liquid evaporates from fields rather than nourishing crops, says James Famiglietti, a hydrologist at the University of California (UC), Irvine. That boosts humidity in the valley, according to previous research, but scientists haven't evaluated its effects farther afield.
So Famiglietti and university colleague Min-Hui Lo employed a global climate model. In one set of the team's simulations, no irrigation occurred. In another set, the researchers added a volume of water equivalent to 350 millimeters of precipitation falling on each square kilometer of the valley's fields between May and October, the time of year when soil moisture typically takes a dive if irrigation isn't provided.
The extra moisture boosted rainfall as far away as western Nebraska and the panhandle of Oklahoma, the team reports in Geophysical Research Letters. Most notably, parts of southern Wyoming and the Four Corners states—Utah, Colorado, Arizona, and New Mexico—received between 4 and 14 millimeters more precipitation each June, July, and August. Overall, that boosts summer rainfall in those areas by 15% above average, which in turn increases runoff into the Colorado River by 28%.
But not all of the enhanced rainfall comes from California moisture, the team notes. As water vapor in the air condenses, it releases prodigious amounts of heat. When that hot air rises, it creates low pressure at ground level in the region surrounding the storms and draws in moist air from surrounding regions, including the Gulf of California and the Gulf of Mexico. "The added moisture really fires up the storm cycle" in the Southwest, Famiglietti says.
The new research "offers one compelling answer to the question of what happens to all of the water evaporated from California's Central Valley farmland," says Lara Kueppers, an ecosystem scientist at UC Merced. The Central Valley is just one of many regions globally that are actively and unsustainably diverting surface water and ground water onto agricultural fields, she notes. "To accurately capture the influence of these regions' on the atmosphere, these massive diversions need to be accounted for."
Yet, climate models typically ignore the effects of moisture from irrigation, Famiglietti says. India, China, and the Great Plains area of the United States are just a few regions where irrigation might significantly humidify the air, and regions downwind are likely receiving increased rainfall as a result, he notes.
Such irrigation doesn't just increase rainfall, adds David Changnon, a climatologist at Northern Illinois University in DeKalb. The enhanced precipitation in Colorado, for example, may be boosting the strength and frequency of local flooding events that commonly occur there in late July and early August.
Also, Changnon says, the findings may provide a glimpse of a future in which the American Southwest becomes increasingly parched. If California ever dials back irrigation because of reduced availability of ground water or reduced flow in rivers now diverted to the Central Valley, precipitation throughout the American Southwest could take a dive. A study of rainfall patterns in the Southwest before the 1940s, when irrigation in the Central Valley became widespread, might provide scientists with a better climatic crystal ball.
-PJ
You are right it has been twenty years since I read it. The title fits the narrative. A whole lot of going up and down mountains. Pretty dry reading if I remember.
Still, my point is there was a lot of surface water throughout California early on. Especially if you believe the maps the greenies use to show how much wetland has been “lost”
The pacific is the great provider of moisture. The coastal ranges may be damp but extract little in my opinion. I absolutly love Sierra thunderstorms when they happen.
More in the Sacramento Valley than the San Joaquin. Tulare Lake was usually a lot smaller than Brewer's observations. The whole region had been greatly affected by the flood.
The pacific is the great provider of moisture.
Not directly. During those summer Sierra thunderstorms, a large fraction of that moisture derived from vegetative transpiration, having hit the ground months before. The reason the thunderstorms are in the mountains is that the moisture laden drift off the Valley floor is pushed higher in elevation to cool. Else, there would be no more clouds than across the Valley itself. You are mistaken.
Damp in Summer I mean. inter is another thing alltogether.
Damp in Summer I mean. winter is another thing alltogether.
lol...
It's 73 degrees with a mild on-shore Pacific breeze and some Pacific Salmon on the grill....37 percent humidity...
I don't think I can take much more Joe!
Honest, if you check out the humidity readings prior to say the late 60s you’ll find a couple percent lower. That’s when cement ponds inundated the San Fernando Valley.
NOt enough to effect anything but still a difference.
Joe, if ya want hellish uninhabitable humidity, try Florida, Texas, and just about any state east of the Mississippi going north from the Gulf region, to the east coast ....In fact, visited some friends in S. Ohio last summer and thought we’d die...Wife nearly scratched by eye balls out...That stuff has a tendency to make people want to go b-e-r-s-e-r-k...Yet about reason why I stay in CA....Life is too short for hell weather...
So? The quantity of rain used in irrigation does not rise to the quantity necessary to lubricate even 2000 democrat dry farts.
Thats the point. Man over states himself. The evaporative quantity in irrigation could not possibly change the moisture content of a flacid democrat lefty arse in Springtime, let alone water the entire Southwestern desert.
I asked for numbers, and this is what you post? You are now proven worthy of no further consideration. Congratulations. I will save this post for future examples of your technical ignorance.
You're lazy too. The first Google search I did yielded the numbers. The California Aqueduct delivers 1.5-1.7 million acre feet per year. This is the equivalent to about four inches of rain per year. This is in addition to well water and water from the Southern Sierra reservoirs. According to the USGS, the peak rate of well pumping in the 1970s was 8 million acre feet per year. That amount has been since reduced to recharge the basin. Total irrigation in the Valley was sufficient to cause as much as 28 feet of surface subsidence, having lowered the water table by as much as 100 feet.
It's a lot of water, most of it lost by transpiration. It grows some 25% of America's produce. I have little doubt that much water transpiration could influence precipitation downwind. It might even be a good thing if we learn how to use the atmosphere to recycle the moisture across the landscape.
While agreeing that a great volume of water can be moved from the area of irrigation due to evapotranspiration, I would disagree that it impacts the southwest. During the spring months here in the southwest (AZ & NM), the predominant wind direction is from the west and southwest and is essentially dry unless the rare low pressure storm dips south and comes our way from California. In the summer months weather is dominated by high pressure rotating clockwise and moving moisture north of the area. When that high pressure moves east, it allows moisture from the southwest Gulf of California and southeast Gulf of Mexico to move into the region bringing on the so-called summer monsoons.
Instead of the Southwest, such valley irrigation moisture would likely be orographically wrung out over the high Sierras or further east over the Great Basin or the mountains of Utah and Colorado.
What is known as a "thermal low" occurs every summer in the area of Yuma, Arizona. Though this area also is irrigated (from the Colorado River), it is also one of the naturally hottest areas of the country. In my experience having lived in AZ & NM all but a few years of my life, it provides little moisture compared to the large negative impact of the aforementioned high pressure zone that is parked over the area from May through mid-July. And any moisture effects of the low pressure from irrigation evapotranspiration seem only to cause a rise in humidity in the local area. The same can be seen in Phoenix where temperatures due to the urban heat effect (black pavement from streets and parking lots, and dark shingles on homes and buildings) combine with evapotranspiration from lawn and vegetation watering to produce a summer misery index that keeps people indoors. It certainly doesn't seem to impact regional weather as the area continues to remain in a lengthy drought.
If you look at my post carefully, you will note that I am not necessarily agreeing with the climatic analysis in the article. I am inclined to be dubious about the quantitative effects cited, as most such “studies” are agenda-driven. However, I am pointing out that there is sufficient water being applied to use evapotranspiration from the irrigated vegetation to advantage as a management principle.
Same here. Meant no disagreement with your posts.
Thanks. I respect you CD, and thought you knew me better than to think me that credulous, so I had to check. I am aware of the weather patterns in NM/AZ, particularly the summer monsoon system, which is entirely different than the exclusively coastal Mediterranean climate we see in California.
BTW, given the terrain and vegetation between San Bernardino and Barstow, I doubt that moisture does very much good for anything. But I do think there's an agenda going on with this article. The left is going for the fantasy that the spread of red brome (sometimes called Spanish Brome, B. madritensis) is the primary cause of the destruction of the xeric annual wildflowers described in the accounts of early explorers. This is in part because their efforts to control the weed have been such a dismal failure (see: "full employment"). So in order to keep the gravy train going, they need a pariah by which their cause can serve as a source of funding (particularly from the foundations invested in global corporate agribusiness and real estate). The goal is to make the landscape SO poor, and so hostile to all life, that the weeds can't (supposedly) make it.
We have a similar scam going here in Santa Cruz, where we have a unique endemic system called "the Santa Cruz Sand Hills." This habitat is being overrun by weeds, notably rip gut brome (B. diandrus) and cat's ear (Hypochoeris spp.). The local "managers" (who show obvious physical evidence of not having done a hard day's work in their lives) are charged with "restoring" more acreage than they can handle. Needless to say, being PC, they'll NEVER use an herbicide and they will never have the budget for "fine scale weeding." They believe that if they can make the land incapable of supporting the weeds, that it will be more native (one problem: I've seen both those weeds grow just fine in washed sand). Accordingly, they are blaming "global nitrate pollution," most of which emanates from China. Needless to say, the only people they can regulate are Americans who are for the most part downwind.
Buncha psychotics. Ain't nothin' quite like leverage. I suspect that the case in this article is the same sort of thing.
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