How to create an evacuation routes overlay

Combine Water Overlay height results with the Travel Distance Overlay to model valid evacuation routes during floods.

How to create an Overlay for calculated evacuation routes:

1. Add a Water Overlay.
2. Set the amount of rainfall of the Water Overlay to a total of 60mm in 60 minutes, followed by 0 minutes of dry period.
3. Add a Combo Overlay, with the Water 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.
4. Add an Area, and draw it anywhere in the project map and with an Attribute named DESTINATION_AREA set to 1. This location will be the evacuation point.
5. Add a Travel Distance Overlay.
6. Under "Keys", opt to use a "blocking input", and select the Combo Overlay created earlier. This will disqualify certain routes from being traversed.
7. Recalculate, and play the Travel Distance Overlay
8. 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.

Notes

• 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.

See also

• Prequel
• Combo Overlay
• Water Overlay
• Travel Distance Overlay