Vanessa Schweizer (left) and Claudia Tebaldi (right), along with their co-authors, have respectively had their scientific papers selected by Environmental Research Letters (ERL) as part of ERL's "Highlights of 2012" collection. Each year ERL editors select the 12 best papers of the year. In their paper, "Modelling sea level rise impacts on storm surges along US coasts," Tebaldi, a Climate Central scientist and NCAR visiting researcher, her Climate Central colleague, Benjamin Strauss, and Chris Zervas, a scientist at NOAA, investigated the changes occurring with sea level rise along the contiguous U.S. coastline, and the resulting likely changes in storm surges.
Erosion along the coast in Hawaii. Copyright University Corporation for Atmospheric Research, Photo by Carlye Calvin.
Many find the worry about exceeding a 2° Celsius (3.6°F) increase in global average temperature at best an abstract idea. Such a temperature increase seems minor – some might argue that a 2°C change may not even be noticeable on any given day. However, the impacts of a higher average temperature have far more discernable impacts to those living along U.S. coastlines where changes caused by rising sea levels resulting from warming climate have appreciable consequences. Among these effects are increasingly dramatic storm surges that, combined with higher water levels, are increasing risk of damage to coastal infrastructure, society, and economies.

Scientists at Climate Central, an independent climate research organization staffed by leading scientists and journalists, wanted to put a more tangible face on changing climate than that offered by the 2°C narrative. Sea level rise is an important outcome of warming climate that has localized, easy-to-communicate effects, explains Claudia Tebaldi, a Climate Central scientist and NCAR visiting researcher. This reality led her, her Climate Central colleague, Benjamin Strauss, and Chris Zervas, a scientist at NOAA to investigate the changes occurring with sea level rise along the contiguous U.S. coastline.

Together, in an award-winning Environmental Research Letters paper[1], the three projected the future effects of sea level rise on storm surges. By combining future global sea level rise with historic tide gauge water levels at 55 sites, the authors found that for about 1/3 of the areas considered, today’s “once in a century” storm surges may become “once in a decade” storms in future.

“Through this study we offer a picture of likely changes in storm-surge return levels and frequency of coastal storm surges in the next decades,” says Tebaldi. “These estimates, depending on the location, may significantly alter risk assessment related to high water levels and should be considered a relevant result for stakeholders and policy makers involved in decisions about coastal infrastructure and environmental protection decisions.”

Focus of the trio’s effort was two fold, first to look at sea level rise at each gauging station, and then to look at storm surges. For the first, the authors looked at the tidal-gauge records to compute the trend in sea level height, comparing results to observed global-average sea level rise. The difference between the two – gauge station sea level and average-global sea level – relates to movement of land at the tidal gauge. For example, says Tebaldi, in the Pacific Northwest, the land surface is rising because the continental plate is experiencing rebound, so in this region sea level rise is lower than is areas where the land is either stable or subsiding.

The scientists then projected the impacts of storm surges and sea level rise that might be expected in the near future (2030), as well as at a point further in the future (2050). Using tidal gauge-station data, they generated a baseline of storm-surge return periods for several representative storm surges at each of the 55 stations. Using model projections of sea level rise, they then generated estimates of relative sea level rise for each station for 2030 and 2050, comparing predicted future outcomes to the baseline observations to see how large storm-surge events might change in the future.

“We did not consider changes in vulnerability or storm strength, instead we did a first-order calculation, that is, by assuming higher sea level rise in the future, we wanted to see what might be expected to happen,” Tebaldi says.

The researchers found that many of the biggest changes in storm surges will occur in locations with the highest degree of sea level rise, which is perhaps not a surprising outcome. The regions that will likely see the highest rise in sea level tend to be in locations of frequent hurricane occurrence, for example along the coast of the Gulf of Mexico. Because of the persistent severe storm threat, people living in these areas have largely adapted to storm surge effects, which lowers future risk for populations living in these regions.

“What is more surprising is that the greatest threats from sea level rise and future storm-surge effects will likely occur along the Pacific coast,” Tebaldi says.

Even a relatively small sea level change may result in large changes in risk because people and infrastructure in these areas haven’t had to deal with the effects of sea level rise, explains Tebaldi. For example, the San Francisco Bay area will likely be more susceptible to storm surges than a city like Galveston. In Galveston, where hurricanes frequently occur, residents live further away from the shoreline and infrastructure is built to withstand severe storms and storm surges. San Francisco has rarely had to deal with flooding or severe storms so risks from storm surges are going to be higher.

“Our results add support to the need for policy approaches that consider that in the future today’s ‘storm of the century’ may become a “storm of the decade,’” says Tebaldi. “These results support the need for policy approaches that consider changes in the frequency of extreme events when evaluating risks from climate change.”
[1] Tebaldi, C., Strauss, B. H., & Zervas, C. E. (2012). Modelling sea level rise impacts on storm surges along US coasts. Environmental Research Letters, 7(1), 014032.


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