These rankings (see my original post) were intended to spark dialogue and are not offered as a rigorous scientific assessment or prediction of future conditions. The rankings can be considered initial hypotheses about which cities are more or less vulnerable to climate change.
For water-supply sustainability and vulnerability to natural disasters, I relied on Sustainlane’s 2008 rankings for those two categories. For heat, I used a data set from Scott Sheridan (Geography Department, Kent State University) which provided the frequency of “oppressive” heat days (encompassing both dry and humid heat) that are associated with heat waves that can threaten health.
Sustainlane’s rankings were organized from 1 (most sustainable/least vulnerable) to 50 (least sustainable/most vulnerable), so I also ranked the same 50 cities for average frequency of oppressive heat days over the past 25 years from 1 (fewest oppressive heat days) to 50 (most). I then found the average ranking for the three categories and ranked the cities overall.
The natural disaster ranking posed a challenge because Sustainlane didn’t distinguish between disasters that may increase with climate change (hurricanes, floods, tornadoes) and those that wouldn’t (primarily earthquakes or tsunamis). To avoid including earthquake risk in these rankings, I dropped the natural disaster rank from cities where earthquakes represent a primary source of threat and thus these cities’ overall rankings reflected an average of water-supply sustainability and heat only. The “earthquake” cities included Seattle, Honolulu, San Francisco, Oakland, Long Beach, San Diego, Los Angeles, and San Jose.
Several of the earthquake cities are also at risk for climate-related disasters included in the Sustainlane ranking, such as flooding, and several of the cities are also at high risk for natural disasters not included in Sustainlane’s ranking, such as landslides and debris flows—both of which can be triggered by intense rainfall events and so their risk could increase with climate change—and wildfire. Both Oakland and San Diego have experienced recent major wildfires and the risk of wildfire is highly likely to increase due to climate change.
The lack of a natural-disaster score reduces the confidence in the overall rank for the earthquake cities. For example, Seattle is currently among the top ten for lowest vulnerability but if the city’s risk due to floods and landslides placed it in the lower half of disaster rankings then Seattle would fall out of the top ten. On the other hand, San Francisco has low risk of most natural disasters other than earthquake and a high ranking for climate-change disaster risk (meaning low vulnerability) would place that city in the top ten. For example, if San Francisco were ranked #1 for natural disaster risk (adjusted to not include earthquakes), then the city would rank as the 7th least vulnerable city for climate change. Clearly, a more rigorous assessment of climate-related natural disaster risk would improve this analysis. However, a more refined assessment of risk for the earthquake cities would likely not produce much change in the top and bottom 10 of the overall rankings.