Feb 14, 2017

What California’s Dam Crisis Says About the Changing Climate

Oroville, CA
Noah S. Diffenbaugh
The New York Times
Riverbend Park in Oroville, Calif., which has seen extremely heavy rains and is threatened by damage to a dam. Photo: Jim Urquhart, Reuters
Riverbend Park in Oroville, Calif., which has seen extremely heavy rains and is threatened by damage to a dam. Photo: Jim Urquhart, Reuters

After five years of record-setting drought, much of California is being pummeled by an extremely wet winter. The disaster unfolding at Oroville, where precipitation is more than double the average, is the latest reminder that the United States needs a climate-smart upgrade of our water management systems.

In the West, much of our water infrastructure is old. Oroville Dam, north of Sacramento, was completed in 1968, nearly a half a century ago. Other major components of our water system are generations older, and maintenance has not been a priority. The damage to Oroville Dam, where the primary spillway developed a giant gash and the emergency spillway threatened to erode, illustrates the hazard of relying on aging infrastructure to protect us from extreme weather.

But age and upkeep are not the only problems. Our water system was designed and built in an old climate, one in which extremely warm years were less common and snowpack was more reliable. Here in the West, we use the same dams and reservoirs for both water storage and flood control, so during the wet season, reservoir managers continuously balance the dual pressures of storing as much water as possible for the dry summer and releasing sufficient water to create room for the next storm.

This system relies on the natural reservoir of mountain snowpack, which melts gradually over the spring and summer. While it is well known that much of the West relies on snowpack for water storage, the vital role of snowpack in flood control is considerably less appreciated. When precipitation falls as snow, it stays in the mountains rather than flowing into reservoirs. This leaves more room in reservoirs to prevent flooding downstream during heavy rainfall.

The recent drought has highlighted the pressure that a changing climate puts on a snowpack-dependent water system. With the shift toward more rain rather than snow, and the earlier melting of the snowpack, water managers need to release water more frequently for flood control. This dynamic is playing out in Oroville now, with the state’s water managers racing to empty water from the dam’s reservoir in advance of storms forecast to arrive Wednesday. Because these storms are relatively warm, they are likely to bring rain to the surrounding mountains, speeding the flow of water behind the dam.

The juxtaposition of five years of hot, dry conditions followed by more rain than reservoirs can store may seem incongruous. However, this is exactly what climate scientists have predicted for Californiasince at least the 1980s: protracted periods of warm, dry conditions punctuated by intense wet spells, with more rain and less snow, causing both drought and floods. Recent work from my lab shows that in fact this pattern is already emerging, with the conditions that create extremely warm dry years and extremely wet years both becoming more frequent.