Wednesday, September 12, 2007

A closer look at sea level risk for the San Francisco Bay region

In previous articles I've pointed to sites like Future Sea Level, which focuses on the prospects and impacts in the San Francisco Bay region and the National Environmental Trust page that shows animations of several major U.S. cities being inundated by rising seas. These give you the general idea, but can't tell you much about incremental sea level rise because the sensitivity of their maps to vertical elevation are so crude. With low vertical resolution, it's difficult to estimate just how much damage will be done a by "minor" sea level rise of, say, one meter.

One of the presenters at the California Climate Change Conference this past Monday was Noah Knowles, a research hydrologist with the U.S. Geological Survey, based in Menlo Park, CA. He presented some new maps of the San Francisco Bay and Sacramento Delta that provide a much more accurate assessment of the risks of inundation due to sea level rise. Here's the PDF of his presentation with samples of their maps. Below is an image of San Francisco showing the Embarcadero and downtown areas.

Using photogramettry - where aerial photographs taken from six different angles were digitally processed to yield maps with vertical scale accuracy of 10-20 cm - combined with tide data, he described the current situation where, on a daily basis, about 500 square kilometers of tidal land and land protected by levees are below water level at high tide. With a 1-meter rise in sea level, that area would increase by 30% and would - under the current circumstances - be inundated at high tide. That would include all of the levee-dependent islands and agricultural lands of the Delta and much developed land surrounding the Bay including much of our highway system.

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