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Risk Migration Review

Post-control review — instantiates Exposure Pathway Interruption

Checks, after a control goes in, whether the hazard actually fell or merely moved — to a substitute route, downstream, or onto a more vulnerable population.

Interrupting one route often doesn't destroy risk — it relocates it. Risk Migration Review is the standing check that asks, after a control is in place, whether exposure genuinely dropped or simply moved: to a substitute pathway, further downstream, or onto a population less able to resist it. Its defining lens is the balance sheet across targets and routes rather than the treated link alone — it pairs a migration watch with an equity-and-hotspot overlay, so a control that shifts the hazard onto a vulnerable community is caught rather than counted as a success. It is a review, not an intervention: it audits where the risk went and states the residual, so the interruption effort doesn't declare a win that only re-labeled the problem.

Example

A town raises a levee to protect its riverfront from flooding. A year later the review runs. The migration watch traces the water: the levee didn't remove the flood volume, it sped it downstream, raising crests at the next town below. The equity overlay shows that downstream town is poorer and less insured — the risk moved onto the population least able to absorb it. The residual statement records what remains: upstream flood risk down sharply, downstream risk up, net regional risk roughly unchanged but redistributed. The review's output isn't a fix; it is the finding that reframes the levee from "solved" to "migrated," triggering a basin-wide look instead of a local victory lap.

How it works

  • Re-trace the hazard after the control: where does it go now that the treated route is cut or blocked?
  • Watch for substitute routes, downstream displacement, and temporal shifting — the hazard deferred, not removed.
  • Overlay equity and hotspots: did the residual land on a more vulnerable group or concentrate somewhere new?
  • State the residual exposure plainly, per target and route, rather than reporting only the treated link's improvement.

Distinct: it evaluates the whole redistribution after the fact, not any single route.

Tuning parameters

  • Review boundary — how wide a system you trace risk across. Too narrow and migration hides just outside the frame; too wide and the review never closes.
  • Migration sensitivity — how small a displacement counts as a finding worth flagging.
  • Equity weighting — how much a shift onto a vulnerable population counts against a control that lowered aggregate exposure.
  • Cadence — a one-time post-implementation audit versus a recurring watch as conditions change.
  • Residual granularity — a single net figure versus a per-target, per-route breakdown.

When it helps, and when it misleads

Its strength is that it prevents "risk migration rather than reduction" — the archetype's signature failure — from passing as success, and it surfaces distributional harm that an aggregate metric hides. Its own failure mode is boundary choice: draw the system frame too tightly and the migrated risk sits just outside it, invisible and uncounted. The classic misuse is running it as a rubber stamp — scoping the review to confirm the control worked rather than to find where the hazard went. The discipline is to fix the review boundary wide enough to contain plausible substitute routes before seeing results, and to weight equity explicitly so a control that helps the average by hurting the vulnerable is not scored as a win.[1]

How it implements the components

  • risk_migration_watch — it traces where the hazard goes after a control and flags substitute routes and downstream or deferred displacement.
  • equity_and_hotspot_overlay — it maps the residual against vulnerable populations and emerging hotspots so redistribution is visible.
  • residual_exposure_statement — it states plainly what exposure remains, per target and route, after the control.

It evaluates outcomes but places no controls: pathway_graph and the reachability check are Pathway Reachability Analysis's, breakpoint_priority_rule is Route Closure or Segmentation's, and the continuous monitoring_probe_network is Sentinel Receptor Monitoring's.

Notes

Its natural trigger is any route closure or barrier that could have a substitute path — Route Closure or Segmentation especially — which is why it reads as the paired conscience of the intervention mechanisms rather than a stage that runs only once at the end.

References

[1] Risk (or burden) shifting — a control that relocates a hazard onto another place, time, or population instead of removing it — is a recognized pattern in environmental-justice and risk analysis; the whole point of this review is to make that shift visible rather than let an aggregate improvement conceal it. ↩