Coming El Nino could replenish Calif.’s aquifers – or ravage vulnerable infrastructure

time, we won’t be able to store a lot of it, and we’ll have to let it go. And it could wreak havoc.”

There is no mistaking the damage that can be done by a flash flood over parched terrain. A torrent of water from an intense thunderstorm in July washed out the supports holding up a bridge on Interstate 10 east of Palm Springs, California. The bridge collapse sent one motorist to the hospital, and a major artery connecting Arizona and Southern California was completely closed for over a week. It took more than two months and several million dollars for traffic to resume flowing in both directions.

While transportation infrastructure is obviously vulnerable, AghaKouchak is more worried about the many levees in place throughout California. In a letter published in the journal Sciencein August, he and other experts stressed that 55 percent of California’s levees are rated as “high hazard,” meaning there’s a risk of their failure in the event of a flood or an earthquake.

These earthen structures, made of soil, are affected by drought in a couple of ways. For one, the dirt itself has dried out and crumbled in places, and cracks have formed. Also, in the absence of rain or abundant surface water, farmers and other water users have tapped into groundwater supplies to an unprecedented extent.

“If we pump a lot of water out of the ground, we typically deal with land subsidence, which is another source of pressure on our earthen infrastructure,” AghaKouchak says.

But there may be some relief if California gets the hoped-for kind of rain: a little at a time over a long period. “You can have subsidence for a certain period of time, but then it can come back if there’s a lot of recharge back to the system,” AghaKouchak says. “But studies have shown that beyond a certain point, land may not behave elastically, and some permanent changes will happen. … The Earth does not respond like a sponge, unfortunately.”

He and fellow researchers at UCI are closely monitoring this season’s El Nino, not because they’re fans of disaster movies, but because of the opportunities it presents to learn about the relationship among ocean temperatures, rainfall, droughts and floods. “UC Irvine is well-poised to study climate extremes. We have faculty from engineering, social ecology, Earth system science and climate physics looking into different aspects,” AghaKouchak says.

“The research community here is very excited. First of all, it’s an extreme El Nino, and we haven’t had many of those in recent history,” he says. “And the pattern of this particular El Nino is different from previous ones. The ocean temperature at the higher latitudes is warmer than average, and we don’t really know how that’s going to impact rainfall, the jet stream or high-pressure ridges in the coming season. Everyone is on edge, waiting to see how this event is going to unfold.”

— Read more in Farshid Vahedifard et al, “Drought threatens California’s levees,” Science 349, Issue 6250 (21 Aug 2015): 799 (DOI: 10.1126/science.349.6250.799-a)