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"So long and thanks for the maps"

"So long and thanks for all the fish, I meant maps (apologies to Douglas Adams)" was the last post in my #30DayMapChallenge report...

Wednesday, 27 November 2019

Coastal Inundation

Local Community Engagement 1234567 & 8

[Update: Part 8 on temperature anomaly scenarios further constrains the debate]

I have since created from Open Data and written in Medium a number of climate change models with regards to sea level rise and coastal inundation. This arose from a statement in my new Cottenham Open LinkedIn channel:
What will East Anglia look like after sea level rise, and in what  time-frame? There's no community engagement without knowing your environment!

Let me start with three statements in the literature that should alleviate any concerns around either sensationalising or debunking Climate Change in the press:
  • Climate Central, whose data are used here, said in Nature Communications: “experts now estimate there is a 5 percent chance 21st century sea-level rise will exceed 2 m.”
  • some to&fro-ing with Climate Deniers brought up the aspect of coastal subsidence & glacial rebound I know&love as a geologist - some coastal regions  like Houston or Bangkok slide into adjoining gulfs as they sit on soft sediment, other regions like Arctic Canada and East Anglia have risen slightly as Quaternary ice shelves disappeared - Deniers wish they'd never asked...
  • right on cue, NASA / JPL scientists  modelled Antarctic ice sheets incl. aspects of the above, and they “ estimated that projections [for sea level rise factoring subsidence &/or rebound] for the next 100 years are within about 1% of previous projections for that same time period. ”

Cambridge North

Of paramount importance, is the extent to which sea level rise would cause coastal inundation. The top clip at left is from Climate Central's recalculation of global topographic maps derived from satellites.The bottom one is from Ordnance Survey Open Data direct calculation of local surveys.

Here we mask in colour potential coastal inundation areas (red to 0.5 and green to 2 m. sea level rise, numbers explained below), and leave transparent below zero (next to red) and above 2m. (next to green)

Note: at the top is a 50x90m grid against 50x50m below, giving it a blockier look.

Click both images to enlarge.

East Anglia

This doesn't mean that all's well, however, as a quarter of the Fenlands could be inundated as shown:

OS OpenData (L), CoastalDEM (R), colour scheme as above

Spatial statistics on the map show that 12% (L) & 14% (R) land is below sea level today in the area above. A simple 2 m. sea level rise will put 22% (L) & 25% (R) land below sea level. Note that these are straight elevation statistics, not environmental modelling such as absorption, run-off etc. And while current sub sea level structures help drain the Fens, such a sea level rise would inundate around 25% of East Anglia! Details are tabled here:
click to enlarge
A 2 m. sea level rise would double the inundation potential and make a quarter of the land un-arable in East Anglia, England's breadbasket
As mentioned in Medium above, part of the climate change risk & mitigation efforts revolve around coastal inundation. We started with a time frame and probability, and we end now with are areal estimate from simple modelling. Again as mentioned in Medium above, all of these are based on relatively simple maps that can be derived by you, concerned citizens, to help you sort fact from fiction. The coastal inundation setting, models and extent are, moreover, written up as a story map.