Feb 22, 2016

The Human Fingerprints on Coastal Floods

by
Strauss, B. H., Kopp, R. E., Sweet, W. V. and Bittermann, K.
,
Climate Central
  • Removes the assessed human-caused component in global sea level from hourly water level records since 1950 at 27 U.S. tide gauges, creating alternative histories simulating the absence of anthropogenic climate change
  • Finds that out of 8,726 days when unaltered water level observations exceeded National Weather Service local “nuisance” flood thresholds for minor impacts, 5,809 days (3,517-7,332 days, >90% confidence interval) did not exceed thresholds in the alternative histories
  • In other words, the report finds that human-caused global sea level rise effectively tipped the balance, pushing high water events over the threshold, for about two-thirds of the observed flood days—the fraction has increased from less than half in the 1950s, to more than three-quarters within the last decade (2005-2014), as global sea level has continued to rise
  • Also finds that within the last decade, at sites along Florida’s Atlantic coast and the Keys, as well as in San Diego (La Jolla), Seattle, and Honolulu, more than 90% of observed flood days would not have occurred if the central estimate for anthropogenic sea level signal were removed
  • Finds human-caused increase in global sea level also accounts for more 80% of the increase in nuisance flood days between the period 1955-1984 and the period 1985-2014 – periods across which flood frequency tripled for study gauges collectively