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San Francisco wants to prepare for extreme weather. So it turned to climate scientists for help – San Francisco Chronicle

As Bay Area storms become super-charged in an era of climate change, San Francisco wants to know how much worse the weather might get, and it’s turning to Lawrence Berkeley National Laboratory for answers.

The lab’s scientists, who have been at the fore of detailing the impacts of global warming on hurricanes and heat waves, have begun modeling Pacific storms so city officials can address San Francisco’s unique vulnerability at the edge of the continent.

The city’s half-million dollar deal with the lab is expected to help city officials decide where to direct millions of dollars in future infrastructure investments, from fortifying San Francisco International Airport to upgrading highway drainage to re-engineering seawalls.

“In order to make decisions about what adaption strategies to implement and what capital improvement money (to spend), we need data points,” said Anna Roche, a project manager who works on climate issues for the San Francisco Public Utilities Commission, which is coordinating the citywide initiative.

Currently, most of the planning that cities and states do to prepare for global warming is based on national and even international climate models. Such science, particularly when it comes to weather, is often too broad for individual locales to tailor their defenses.

Scientists at Lawrence Berkeley Lab are among a growing body of researchers who have been working to tease out the influence of climate change on specific events in specific areas.

Using one of the world’s fastest computers with an uncanny ability to factor any number of climate variables, the lab’s team has deduced that hurricanes Katrina, Irma and Maria dropped 5 to 10 percent more rain because of the warmer atmosphere. They found that a 2015 heat wave in India and Pakistan that killed nearly 4,500 people was as much as 1,000 times more likely because of the hotter climate.

The impacts of climate change are expected to only grow as greenhouse gas emissions continue to heat the planet.

Scientists Chris Patricola and Michael Wehner at Lawrence Berkeley Lab who are developing the storm model for San Francisco hypothesize that global warming will pack increasing amounts of rain into West Coast storms, simply because hotter air holds more moisture. But they don’t know how much more rain will come nor do they know how the changing circulation of storms will affect factors like wind and sea surges.

The lab’s work, which will simulate future storms based on past events and higher greenhouse gas concentrations, is expected to provide a more complete picture of what San Francisco should anticipate

The simulations will narrow the likely impacts of global warming to within as little as two miles, meaning city officials will know precisely how weather in San Francisco will differ from other parts of the region.

“The Bay Area would (normally) be all in one grid box. There wouldn’t be any differentiation between San Francisco and the Peninsula,” Patricola said. But “due to the advances in the supercomputing, we can do this at even finer and finer resolutions.”

City officials hope to begin learning the results of the the lab’s work in about a year. They expect to be one of the first cities in the nation to have models for extreme weather at the local level.

Kurtis Alexander is a San Francisco Chronicle staff writer. Email: kalexander@sfchronicle.com Twitter: @kurtisalexander

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