Preparing for El Niño Using Climate Change Forecasts
Most years, USGS research geologist Patrick Barnard and his colleagues quietly develop detailed coastal hazard forecasts that include the effects of climate change. This year, coastal managers in southern California are clamoring for early results. Some of those forecasts are a good stand-in for El Niño-enhanced storms.
El Niño is the common name for unusually warm eastern Pacific Ocean surface temperatures along the equator. These changes in ocean heat affect weather around the world. Sea surface temperatures measured during the 2015–2016 El Niño have set new records. Intense El Niño winters typically bring much stronger storms to beaches and cliffs along the west coast of the United States, particularly in California.
“When we have these extreme El Niño events,” said Barnard, “we get an increase in wave energy of about 30 percent that results in about a doubling of the typical winter beach erosion in California.” People who maintain coastal infrastructure want to know what this means for sewage treatment plants, highways, and harbors.
Detailed forecasts for a changing world
The USGS Coastal Storm Modeling System (CoSMoS) makes detailed long-range forecasts of coastal erosion and flooding caused by climate change, sea level rise, and storms. Unlike most coastal hazard forecasts, CoSMoS is dynamic. “The idea is that as the climate is changing, the wave climate will change,” said Barnard. “We can’t understand that just by looking at the last 20 years of data from a wave buoy.” CoSMoS shrinks global climate forecasts to a local level, and uses the physics of tides, waves, and river flooding to make detailed projections of coastal flooding. “You look at the broad scale, be it changes in [air] pressure or any changes in sea level,” said USGS oceanographer Andy O’Neill. “Then you funnel down to find the regional impacts and then the local scale impacts.” CoSMoS flood forecasts go down to 2-meter (6.6 foot) sections of the coast.
Project leader Barnard and a team of USGS scientists developed the first version of CoSMoS for southern California starting in 2011, then improved and applied CoSMoS to the north-central California coast and San Francisco Bay in following years. Now Barnard, O’Neill, and their colleagues are back in southern California, working on CoSMoS 3.0. For this version, they are collaborating with top coastal and climate scientists from the Scripps Institution of Oceanography, Oregon State University, and private companies. The team is adding long-term changes to beaches and cliffs, local seas and storm surge from global climate models, and flooding from rivers. They are distributing initial results quickly, to meet the needs of coastal managers who must respond to El Niño storms.
“There’s 40 different scenarios of sea level rise and storms for the whole region,” said Barnard. “It’s about 500 kilometers (300 miles) of shoreline. State agencies, local agencies, and others need this kind information to understand the potential impacts long term, so they can manage their resources appropriately.” USGS scientists developed CoSMoS scenarios and forecast products in collaboration with federal, state, and local governments. They included sea level rise scenarios in several steps from 0 to 2 meters (6.6 feet), plus 5 meters (16.4 feet), rather than using specific years such as 2050.
“We’ve tried to take the timestamp off of it, because sea level rise projections are very uncertain and the science changes,” said Barnard. “We try to keep it as flexible as we could so the flooding projections wouldn’t become obsolete.”
Adding scenarios with zero sea level rise was the key to using CoSMoS forecasts during an El Niño winter. “We purposely developed a number of scenarios that do not include sea level rise at all—just storms,” said Barnard. “Those scenarios are a pretty good proxy for El Niño-type storm impacts.” The California Office of Emergency Services uses those scenarios now.
In high demand
“There were close to 100 people,” said O’Neill, describing her presentation on “El Niño: What to Expect for southern California.” She gave her talk in the fall of 2015 as part of a University of Southern California webinar series. “It seemed to be a whole range of people from contractors who will be using our results, to somebody from the Aquarium,” she said. “There were people with water districts, city planning and resource councils, and regular public users.” O’Neill also gave the presentation to civic groups who wanted to know more about the possible harmful effects of El Niño.
At the request of the California Ocean Protection Council, the Governor’s Office of Emergency Services, and other agencies, Barnard presented overviews of the CoSMoS forecasting process and initial forecasts along four sections of the California coast: Los Angeles County, Orange County, San Diego County, and Santa Barbara and Ventura counties combined. After each of his presentations, many of the questions focused on cliff erosion and flooding.
Most important forecasts
Two CoSMoS forecasts are most useful during an El Niño winter. The worst El Niño storm could look a lot like a 100-year storm with no sea level rise—one of the 40 CoSMoS scenarios. In southern California, coastal flooding from a storm like that could be a problem in a number of locations. Unfortunately, one of those locations is the Port of Los Angeles. “The economy basically flows through that port,” said Barnard, “We’re trying to give people an understanding of the potential risk through flooding and coastal change.”
Other high-value areas in southern California that could be flooded during one of these storms include parts of Goleta, Long Beach, Newport Beach, and San Diego.
The other critical CoSMoS forecast for southern California is cliff erosion. “There’s tons of communities that are built right on the cliff edge,” said Barnard. “That’s going to be a much bigger factor for them, as opposed to coastal flooding.” Several of those cliffs are at high risk of collapse during and after intense storms.
Many different factors affect cliff erosion. “Surprisingly, there haven’t been a lot of cliff models that utilize all the different factors,” said Barnard. “It’s kind of hard to include them all.” USGS geologist Patrick Limber is working on cliff erosion forecasts that include waves, rain, and sea level rise, three of the most important factors.
Improving and expanding coastal hazard forecasts
The initial CoSMoS data for southern California is ready to use in Google Earth or ArcGIS mapping software. This summer, USGS and partners plan to add the finished forecasts to Our Coast, Our Future (http://data.prbo.org/apps/ocof/). The web site helps anyone zoom into detailed forecasts of coastal flooding, cliff erosion, and related information, without a crash course in computer mapping.
Further developments of CoSMoS are underway. According to Barnard, the next major version should include the harmful effects of coastal flooding and seawater contamination on groundwater. The team also plans to look at the potential impact of hurricanes. Even though only two hurricanes have hit southern California in the past century, the number and strength of these storms could change as the climate changes. USGS geographer Nathan Wood plans to add forecasts of coastal hazard effects on the local economy and population. In addition, the team wants to provide CoSMoS forecasts for other areas.
After completing work in southern California this year, Barnard and his colleagues plan to work on central California in 2017, then in 2018 study the California coast north of Bodega Bay. “We’re currently developing plans in Puget Sound,” said Barnard. “Then there are also preliminary talks about moving it to Hawai’i and the north slope of Alaska.” CoSMoS forecasts for these areas could help coastal resource managers prepare for long-term climate change—and the next El Niño winter.
in this issue:
Preparing for El Niño Using Climate Change Forecasts