(The first story in my intermittent series about water issues and the future of our most valuable resource.)
On the surface, water is scarce in the Mojave Desert. But, in southwestern California, below the rough, rocky ridges and desolate dry lakes, a large reserve of groundwater has been slowly growing for centuries. The Cadiz aquifer holds more water than the country’s largest surface reservoir, Lake Mead, about 100 miles north and west, where the Colorado River meets the Hoover Dam.
A controversial project to “harvest” water from this aquifer and is moving closer to reality after more than 15 years in development. The design calls for pumps to move the water south through more than 40 miles of pipeline to join an aquiduct that brings water from the Colorado river to thirsty coastal California. Here’s a map. The Cadiz Project plans to drain between 50,000 to 75,000 acre-feet per year from the aquifer. An acre-foot of water is the standard measure for reservoirs, a volume of water that is one acre square and one foot deep. One acre-foot of water is the estimated use of a suburban household, annually. (I also wrote about this issue for BestThinking here)
The proponents of the project claim that the groundwater harvesting will be sustainable. The aquifer is slowly recharged by the natural rain and snow that fall on the mountains and valleys across the region, slowly trickling down into the subterranean basin. The region receives between 3 and 9 inches of rainfall annually, about 3 in the valleys, and up to 9 in the tall mountain ranges, which can be snowy through the winter. (For comparison, the average rainfall in Madison, WI, is 32 inches) The Cadiz pipeline intends to pump out more water than naturally recharges. However, water is also lost annually to evaporation at the surface of the dry lakes that sit directly above the aquifer. Cadiz plans to intercept this water and pump it away. See their diagram here.
The first problem that jumps out to me is that water is not actually “lost” to evaporation. As many of you may remember from elementary school, evaporation is a key step in the water cycle, returning moisture to the atmosphere that turns into future rainfall. If you reduce the water available for evaporation, over the long run you decrease the water available in the region for precipitation.
Beyond the faulting logic of protecting water from evaporation, Cadiz proponents claim that they will only drain the aquifer for 50 years, giving it the next 50 to recharge. However, it’s hard for me to believe that once they build this extremely expensive pipeline, they’ll be able to resist the economic pressures to produce and sell as much water as possible from their infrastructure investment.
The Cadiz aquifer lies just south of Mojave National Preserve, quiet national parkland that everyone speeds past on I-40 between Los Angeles and Phoenix, clueless about park’s the high granite peaks, towering sand dunes, and sprawling forests of the Mojave’s iconic Joshua trees. All of the parks wildlife and many rare and endemic plants depend on the small springs spread across the dry landscape. Thankfully, these seeps and springs will not be damaged by the aquifer-draining plan, they are fed by water percolating through the mountain long before it reaches the low elevation aquifer. (NPS info on spring safety here)
Despite the springs, droughts are common here. When I worked to make the vegetation map of Mojave Preserve, the crew of fire fighters stationed there told us the story of a recent summer when most of the springs had dried up. One small pool of water remained, deep in a big rock crevice, and burros were throwing themselves into the hole, desperate to reach the water, and dying, one after another, in the process. Although depressing, droughts are part of natural climate cycles. But, I’m afraid that long term plans that reduce the water cycling in the region will undoubtedly affect the plants and animals already living in a dangerously dry environment.
Beyond that, climate change models predict that the Mojave Desert region is going to become hotter and drier over the coming decades. These changes do not seem to be factored in to the Cadiz project’s calculations about how much water they can “safely” drain from the aquifer. I know that Southern California wants the water, and they are not the only part of the Western United States experiencing drought and decreasing water reserves. However, tapping into a reserve of groundwater that took centuries to accumulate to pump off more than the natural recharge seems unsustainable and shortsighted. A similarly sized investment in water efficiency across the LA valley could probably make a serious impact on the region’s water shortage. A desalination plant that could turn salt water into fresh water, while an expensive investment, wouldn’t run out of reserves in 50 years that way this groundwater plan would. We all need water to live, but that doesn’t mean we should make environmentally risky decisions about how to produce more of it.