How to create an evacuation routes overlay
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By combining the output of the Water Overlay's results on water heights, and the Travel Distance Overlay, it is possible to create a calculation model for valid evacuation routes in the event of a water calamity.
How to create an Overlay for calculated evacuation routes:
- Add a Rainfall Overlay.
- Set the amount of rainfall of the Rainfall Overlay to a total of 60mm in 60 minutes, followed by 0 minutes of dry period.
- Add a Combo Overlay, with the Rainfall Overlay set to input A, and a formula of "GT(AT, 0.2)". This computes all places where a route would be blocked (1) or not (0), by having more than 20cm of water stress.
- Add an Area, and draw it anywhere in the project area and with an Attribute named DESTINATION_AREA set to 1. This location will be the evacuation point.
- Add a Travel Distance Overlay.
- Under "Keys", opt to use a "blocking input", and select the Combo Overlay created earlier. This will disqualify certain routes from being traversed.
- Recalculate, and play the Travel Distance Overlay
- Notice that as the simulation progresses, the green evacuation routes will be supplanted with red indications that the road is experiencing too much water stress.
- The setup could be further expanded on by adding an additional Combo Overlay which takes into account which locations were once a valid route but later weren't, thus highlighting all the locations which become cut off from evacuation routes.