News from Berkeley Lab

Extreme Weather Expert: How Climate Change is Intensifying the Winter Storms Slamming California

As another atmospheric river impacts California on January 4th and 5th — with more rain forecast after that — Michael Wehner, a senior scientist in the Computational Research Division at Lawrence Berkeley National Laboratory, discusses how climate change is increasing the rainfall from these drenching storms and how people can better prepare. Wehner uses observational data and advanced computer modeling to understand the behavior of extreme weather events in a changing climate, especially heat waves, intense precipitation, drought, and tropical cyclones.

Michael Wehner: There are many kinds of storms that impact California and the Bay Area. This particular storm is an atmospheric river with a large extratropical cyclone, sometimes called a bomb cyclone because of a rapid pressure drop.

Our research, joint with the San Francisco Public Utilities Commission, has developed the relationship between temperature change due to humans and atmospheric river precipitation changes. Climate change has the greatest effects on storms like this one, which is an atmospheric river with a large extratropical cyclone. As there is about a 1 degree Fahrenheit of climate change induced warming in the waters off of San Francisco, our relationship says that the storm total precipitation should increase by about 5%. But bear in mind that shorter, intense periods of rains during this storm could be increased by even more.

Well, you can expect a lot of rain and a lot of wind, possibly some flooding and mudslides in some regions. Because we just had a storm, the ground is already wet. Climate change increases the rainfall in this storm by about 5%, which further increases the risk of these types of hazards.

Well, knowledge is power and our infrastructure was not designed for the storms we have today, but rather for storms of maybe 50 or a hundred years ago. As the climate continues to warm, these very intense storms will become even worse. Knowing this in advance helps decision makers and planners with the information they need to adapt our systems to be more resilient.

Storms like this one and the fact that climate change has an attributable effect on it demonstrate that dangerous climate change is already here. This is not our grandchildren’s problem. It is our problem. The sooner we recognize that, the sooner we can take actions to adapt to these changes and the sooner we can take actions to mitigate our dependance on fossil fuels.