What We Know About Hurricane Helene's Destruction So Far

FEMA flood maps show the hospital in a zone with "0.2% annual chance flood hazard", a/k/a a 500-year flood. Map dates to 2008, and I suspect risks have changed:

"The flood map for the selected area is number47171C0152C, effective on9/3/2008"

<https://msc.fema.gov/portal/search?AddressQuery=Erwin%2C%20T...>

A 1000 year flood, perhaps, based on 2008-era flood risk maps. The facility was built within a 500 year (0.2% annual flood risk) basin. It's on a flat escarpment surrounded on three sides by the Nolichuky River, in a region characterised by steep terrain and narrow river valleys.

The sort of terrain in which if, or rather, when a major tropical storm (or its remnants) moves through will be subject to high levels of flooding.

I'm focusing on the Unicoi hospital largely as I'd heard of the heliocopter rescues from it in earlier broadcast news reports, but nothing of its specific situation, when it was planned and built (within the past decade), or the fact that what should have been a major feature of rescue and recovery capabilities was in fact a rescue and recovery target, both diverting resources from elsewhere and eliminating a local point from which aid could have been rendered and coordinated.

A much broader point is that this is all but certainly not an exceptional case, and that there are likely similar facilities, or other high-risk activities (e.g., nuclear fuel servicing, a half mile upriver) which are similarly at risk, in Tennessee, surrounding states, and elsewhere in and outside the US, and that a comprehensive review and remediation effort based on identifying risks, updating flood maps, and mitigating or moving both first-responder and other high-risk facilities outside flood or other risk areas be addressed.

Climate is changing rapidly, and one characteristic I'm observing are large, moisture-laden, slow-moving storms (Florence (2018), Harvey (2017), and of course Katrina (2005)) which dump immense amounts of rain over side areas. Harvey in particular dumped over 1000mm (40in) of rain over Houston and surrounding areas (peak: 1,539 mm / 60in),[1] which at one tonne per square metre of land actually caused the land in the region to measurably lower, as I recall. (I'm not finding a citation for this, though I'm reasonably certain of my memory. Total rainfall exceeded 16 trillion gallons, or ~63 billion tonnes: <https://apnews.com/article/science-floods-storms-hurricanes-...>.)

There are numerous communities which likely suffered similar impacts as Erwin, TN, and far more which are at risk of future extreme inundation events. And NOAA/NHC are presently five tropical storms in the Atlantic basin, another two in the Eastern Pacific.

<https://www.nhc.noaa.gov/?atlc> <https://www.nhc.noaa.gov/?epac>

Longer-range forecasts (through about 5 October) show potential for more Gulf-originating storms as well. We're hardly through this season yet. Rumours are that there will be other seasons afterward.

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Notes:

1. <https://en.wikipedia.org/wiki/Hurricane_Harvey#Texas_2>