Global Warming, Storm Surges & the Mother Of All Desert Floods | KCET
Global Warming, Storm Surges & the Mother Of All Desert Floods
This week's flooding in the desert, as dramatic as it was, was nothing too far out of the ordinary. The Low Desert has seen its share of far-greater floods, from the periodic emptying of the Colorado River into the Salton Basin that created ancient Lake Cahuilla -- actually a series of gigantic lakes that drowned the Imperial and Coachella valleys repeatedly over the course of the last few thousand years -- to the 1905 engineering fiasco that created the Salton Sea, a much smaller version of Lake Cahuilla. In fact, the creation of the Salton Sea was only the largest of the floods in the post-European-contact era: according to the Salton Sea Authority, Colorado River floods filled at least some of the valley no fewer than eight times between 1824 and the creation of the Salton Sea.
The Colorado River may fill the Salton Basin with water every now and then, but if it weren't for the Colorado, the Salton Basin would be much wetter. Without the Colorado, the Basin would be part of the Sea of Cortez. As rising sea levels are increasingly on the agenda for global discussion, it's worth wondering -- Could the Sea of Cortez ever come back to reclaim the land of the Imperial and Coachella Valleys?
For millions of years, the Colorado River has been carving canyons in the southwest, including that Grand one. Young-earth creationists, seeking to undermine the principles of the science of geology, sometimes ask where all that sediment went if the Grand Canyon was actually carved by natural causes. The answer? Mexicali. And Indio. The Coachella and Imperial Valleys -- and the Mexicali Valley that constitutes the Imperial Valley's cross-border extension -- sit atop as much as 16,000 feet of that sediment. As the river filled the Salton Trough with sand and silt, it built a berm across the younger part of the Colorado Delta: a stretch of relatively higher ground that reaches its peak -- about thirty feet above mean sea level -- between the present-day cities of Mexicali and Guadalupe Victoria about twenty miles south.
That berm protects the farm fields and cities of the Salton Basin, which lie as much as 200 feet below sea level, from the Sea of Cortez. It wouldn't take much to fill the whole of the Imperial and Coachella Valleys with seawater, if we wanted to: all we'd need to do would be to dig about a hundred miles of canal from the Gulf to breach that berm, the banks of which would need to be no higher than 30 feet anywhere along its length.
Of course we'd be displacing more than a million residents of Mexicali and the Imperial and Coachella valleys, disrupting transportation networks vital to continental trade, despoiling hundreds of thousands of square miles of ecologically intact desert and wetland, and causing untold billions of dollars in economic damage -- perhaps trillions.
Clearly, we'd be crazy to do this on purpose. But we may be setting ourselves up to do it by accident.
Predicting sea level rise due to human-caused climate change is a risky venture. The Intergovernmental Panel on Climate Change (IPCC) predicted in its 2007 Fourth Assessment Report that sea level in the year 2100 might be as high as half a meter or so if we don't get serious about our bad habit of adding greenhouse gases to the atmosphere. (We seem not to be getting serious about that, at least in the US.) Half a meter doesn't seem like much unless you have oceanfront property, until you consider the effect of higher water on storms, erosion of protective barrier islands, and the like. Still, given the Salton Trough's 100-mile-thick, 30-foot high protective seawall -- about nine meters -- half a meter higher seas doesn't seem much of a threat.
(That's mean sea level, of course. High tides at the north end of the Sea of Cortez can reach two meters. Still.)
2007 is, however, four years in the past. The IPCC cautioned that their 2007 calculations didn't include increased movement of glacial ice sheets, and we've learned a fair bit of bad news about ice sheets since. Ice on water floats isostatically, like ice cubes in a drink; it can melt without raising the water level. But ice sheets on land do add to sea level rise if they melt, as long as their meltwater eventually reaches the ocean. Three large reservoirs of terrestrial ice pose significant concern to climate modelers: Greenland's ice cap, the West Antarctic Ice Sheet, and the East Antarctic Ice Sheet, which is the largest of the three.
As global climate warms, those ice sheets may become increasingly unstable. The West Antarctic sheet is increasingly feared to be on the verge of collapse, which event would raise sea level by three to five meters. Greenland's ice sheet is dwindling far faster than even some pessimistic climatologists had feared, and its collapse would mean a seven-meter jump in sea levels. Some scientists think that warming climate may mean more snowfall and colder overall temperatures in the Antarctic, which could keep the East Antarctic Ice Sheet more or less stable, but more recent research indicates that may not be a sure thing.
If the East Antarctic ice goes mean sea level could rise by 60 meters, in which case Southern Californians will have a lot on their minds other than the fate of the Salton Basin. But let's ignore that for now. Melting the East Antarctic, even under the worst possible human-caused climate change, would take some centuries. The West Antarctic and Greenland ice sheets are melting faster than anyone let themselves speculate back in 2007. Greenland ice experts are using words like "shocked" and "gobsmacked" to describe their reactions to the receding of that island's ice in the last two years.
Based on such updated information, climatologists are now predicting, off-the-cuff, rises of a meter by 2100 rather than the IPCC's more conservative forecast.
Still, no one knows exactly how soon Greenland's ice, or the West Antarctic Ice Shelf, will go. It will likely be sooner, and more suddenly, than we expect. When both of those reservoirs of ice are gone, we can expect sea levels to be ten to twelve meters higher than they are now, which would mean the Colorado River delta berm across the mouth of the Salton Trough will be submerged, and oceangoing ships will ply the waters above what was once Indio.
Truth is, we won't actually have to wait for sea level to rise high enough to overtop that berm before the Sea of Cortez reclaims the Coachella Valley. As sea level rises, the power of storm surges rises with it. If you wanted to amplify the effect of storm surges on purpose, it would be hard to design a better place to do that that the Sea of Cortez, with its long, tapering shape pointing in the direction of tropical storms' prevailing winds. Water can pile up to prodigious heights at the head of the Sea. Even at current sea level the Sea of Cortez is no stranger to 18- or 20-foot storm surges. Just a couple meters' rise in mean sea level, coupled with a high tide and a 100-year storm, could send a sheet of seawater surging across the flat fields of northern Baja. The soil there is alluvial and easily eroded. One really big storm might carve that sea-level channel without our help -- aside from the help we provided by changing the climate. And then there would be nothing to stop the process, a flood seeking the easiest path to the floor of the Salton Basin 200 feet down, the weight of the entire Pacific Ocean behind it.
Harold Bell Wright, in his 1911 historical novel "The Winning of Barbara Worth," described the violence with which the Colorado tore through irrigators' unlined canals in 1905 during the Salton Flood, and his prose serves well to give a hint at the ferocity with which the ocean might invade the Valley:
Will this actually happen? Almost certainly, though the collapse of the ice sheets may not take place until two or three centuries from now. And long before the water rises high enough to reclaim the Salton Trough, rising waters in coastal areas will cause intense human misery and environmental damage. Look at the landscape with a long enough view, and the processes that shape the Low Desert hint at an ever-broadening, ever-lengthening arm of the ocean, as tectonic plate grinds against tectonic plate and the crack that is today's Sea of Cortez grows northward.
Still, what may be inevitable on the scale of millions of years doesn't necessarily need to happen when your great-grandchildren's grandkids are in college. Add this to the many reasons to help slow the changing of the climate: those far off-descendants in college should have the chance to rock out at Coachella without a snorkel.
Chris Clarke is an environmental writer of two decades standing. Author of Walking With Zeke, he writes regularly at his acclaimed blog Coyote Crossing and comments on desert issues here every Wednesday. He lives in Palm Springs.
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