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Thread: Bike Tour of Climate Impacts in DC

  1. #41
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    Quote Originally Posted by DismalScientist View Post
    Thank you for that website as it proves my original statement. If you fiddle with the assumed level of sea level rise you will find that there is a 65% chance of an 8 ft flood by 2050 under a "medium rise" scenario. Under a "slow rise" scenario, that chance falls to 60%. Under a "fast rise" scenario, it is 70%. In other words, the chances that we see an 8 ft flood by 2050 is barely related to the speed of sea level rise, which was my original statement.
    Wouldn't you need to test fast rise against zero rise? Slow rise still assumes some global warming.

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    Quote Originally Posted by lordofthemark View Post
    Wouldn't you need to test fast rise against zero rise? Slow rise still assumes some global warming.
    The website is very opaque on the assumptions underlying the different scenarios. I don't know how to get predictions for a zero rise.

    Here's an interesting graph from the EPA:
    https://www.epa.gov/climate-indicato...tors-sea-level

    My interpretation is that a zero rise null hypothesis might be inappropriate.

  3. #43
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    Quote Originally Posted by DismalScientist View Post
    The website is very opaque on the assumptions underlying the different scenarios. I don't know how to get predictions for a zero rise.

    Here's an interesting graph from the EPA:
    https://www.epa.gov/climate-indicato...tors-sea-level


    My interpretation is that a zero rise null hypothesis might be inappropriate.

    It seems possible that the modest difference in flood risk between the slow rise scenario and the fast rise scenario reflects that any reasonable low end estimate of global warming leads to a significant rise. Ergo, OP's initial statement may not be at all misleading.

    I sympathize that it is difficult to do the analysis to challenge the implications of the OP's statement (not the statement itself, which is clearly true) - in that case it seems like the best thing would be to just leave the OP's statement alone.

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    Quote Originally Posted by lordofthemark View Post
    It seems possible that the modest difference in flood risk between the slow rise scenario and the fast rise scenario reflects that any reasonable low end estimate of global warming leads to a significant rise. Ergo, OP's initial statement may not be at all misleading.

    I sympathize that it is difficult to do the analysis to challenge the implications of the OP's statement (not the statement itself, which is clearly true) - in that case it seems like the best thing would be to just leave the OP's statement alone.
    When I altered the size of the flood rather than its likelihood, my original "analysis" actually did assume zero rise.

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    I'm not sure what you are even arguing.......... Original post stated:
    "Did you know that DC has a 65% chance of seeing a flood over 8 ft in the next 30 years?"

    It then followed up and stated the climate change is spurring sea level rise. That's not the same thing as saying that sea level rise will be the predominate driver of the 8-ft flood................... (I seriously can't use enough '......' )

    Looking at the published Flood Insurance Study for Washington D.C. (hosted by FEMA, linked here: https://msc.fema.gov/portal/advanceS...hresultsanchor), the Potomac River and the Anacostia River have a 1:50 year (2% Annual Exceedance Probability) flood stage of roughly 8.8-ft (datums are important). Over 30 years, the chance of a 2% AEP event NOT occurring is 54.5%. So based upon the best available data for these two major flooding sources, it is reasonable to suggest that a flood with a stage in excess of 8-ft NAVD88 has greater than 45% chance of occurring at least once. The 25-year (4% AEP) flood stage is 7.4-ft - 29.4% chance of not occurring.

    So...... 45% chance of flood greater than 8.8-ft in the next 30 years, 70% chance of flood greater than 7.4-ft. 65% might be a little generous, but it's not out of the realm once we look at future impacts.
    Last edited by Brett L.; 05-15-2019 at 01:09 PM. Reason: Math is hard

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