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Rain in the Desert: Monsoons, Flash Flooding, and Wildflowers

Ocotillo and storm clouds. | Photo: Dan Eckert/Flickr/Creative Commons License

It was one of those things that a casual passerby might not notice, or even a local unused to paying attention to that kind of detail: the wind turbines at San Gorgonio Pass were spinning in the wrong direction yesterday.

If you stand in the Coachella Valley and face westward toward the coast, the windmills generally appear to spin counter-clockwise. The prevailing winds blow eastward through the pass, carrying their load of Inland Empire smog to the desert. The winds are strong and reliable, which is why power companies have installed millions of dollars of wind turbines just east of the pass. Yesterday those turbines were spinning clockwise instead of counterclockwise. The wind was blowing the wrong way, out of the desert and through the pass toward Los Angeles.

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And it was humid. The air was Midwest moist, shirts sticking to skin moist, and clouds blanketed the desert giving the sky an unearthly pallor. In Joshua Tree and down the hill in the Coachella Valley the air was scented with wet creosote, as if the damp rolling down off the mountain faces had brushed up against the resinous shrubs along the way.

In other words, it's monsoon time in the desert.

Water vapor image from July 30, 2012 | Image courtesy NOAA

The satellite image here was taken yesterday, using a wavelength of infrared radiation to which water vapor is opaque. Where you see white, that's where the atmosphere is heavy with moisture. The big clear area over Texas and New Mexico is a high-pressure zone that's causing extreme temperatures in the southern plains. The air in that high pressure zone is spinning clockwise, and drawing air off the Gulf of Mexico and Sea of Cortez. In the image, that air is the big white tongue coming from the bottom of the image and curling over to the right. It's white because it's full of moisture, evaporated off the ocean during the heat of the day.

In other words, that high-pressure cell over the Rio Grande is pumping water vapor into the desert, and a whole lot of it. This happens almost every year, and is referred to locally as monsoon season, though it's nowhere near as wet as the South Asian season from which it borrows the name. This is a particularly strong monsoon system. Jim André, the director of the University of California's Sweeney Granite Mountains Desert Research Center and a bit of a weather enthusiast, says that this system has more "precipitable water vapor" -- moisture that could conceivably fall as rain or snow -- than any system to hit the desert since Hurricane Isis in 1998.

Monsoon weather is usually characterized by lots and lots of small, intense storms, unlike the characteristic three-day deluges that come in winter along the Pacific Coast. As Deanna Neil notes today, climate change may well make these storm systems stronger. So far, this system has been making itself felt much more strongly in places other than Joshua Tree and Palm Springs, where I happened to spend the day yesterday. Kingman, Arizona got hit hard by rain, as did Tucson. Friends reported that it has rained in Brawley and Beaumont. Borrego Springs saw rain all day, and flooding closed both S-22 and Highway 78 out of Anza-Borrego Desert State Park. Rain caused at least one accident in Cathedral City -- right next to mainly unrained-on Palm Springs, an indication of just how small these storms can be.

Though there were flash flood warnings in the Morongo Basin and a bit of rain in the highlands of Joshua Tree National Park, , the system's contribution to this part of the High Desert was mainly dramatic afternoon skies, culminating in a gorgeous though ominously orange sunset. Today may be different. As that high pressure cell spins ever clockwise, the band of wet air seems to be edging ever more northwesterly. Those of us between 29 Palms, Vegas, and Ridgecrest may get some much-needed rain today, at least here and there.

If you're nearby, there are two things that bear keeping in mind about monsoons like this:

  1. 1998's Hurricane Isis was followed by a really good spring for bloom, so start thinking about March wildflower excursions to the desert, and
  2. Until then, watch out for flash floods. Wait for another week to go hiking in California slot canyons, and if you're driving along and come upon a flood of water crossing the road in a low spot, do not try to drive through the flash flood.

Desert writer Craig Childs wrote that the two easy ways to die in the desert are thirst and drowning, and that's what he was talking about with the last part of his sentence. People die when they try driving through flash floods, or if they're lucky they merely destroy their vehicles. It happens often enough that the state of Arizona passed a law saying that people who drive into a flooded roadway can be charged for any expenses related to their rescue. This law is locally known as the Stupid Motorist Law. 'Nuff said.

Chris Clarke is an environmental writer of two decades standing. Director of Desert Biodiversity, he writes from Joshua Tree regularly at his acclaimed blog Coyote Crossing and comments on desert issues on KCET weekly. Read his recent posts here.

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About the Author

Chris Clarke is a natural history writer and environmental journalist currently at work on a book about the Joshua tree. He lives in Joshua Tree.
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