Early Warning Lead-Time vs False-Alarm Simulator

Sensor Network

Detection threshold θ 0.45

Buoy network size 8 buoys

Dissemination & response latency 12 min

Storm approach window 150 min

Live Status

Phase: Quiet — monitoring baseline

Lead time delivered

—

False-alarm rate

0.0%

Population evacuated

Storm cycles run

Network signal x̄ vs threshold

0.00 / 0.45

How it works

Each buoy measures the true hazard intensity s(t) plus independent sensor noise: xᵢ = s(t) + N(0, σ²). Averaging n buoys gives the network estimate:

x̄ = (1/n) Σ xᵢ
Var(x̄) = σ² / n   → noise shrinks as 1/√n

Alert fires when:  x̄ ≥ θ  (detection threshold)

This is classic signal detection theory: raising θ cuts false alarms during quiet periods but delays real detections, while a bigger sensor network (larger n) narrows the noise band around the true signal so a lower, faster-triggering θ stays safe — the core trade-off behind every real buoy/gauge early-warning array.

The Sendai Framework for Disaster Risk Reduction names four pillars a warning chain must complete before impact: (1) risk knowledge, (2) monitoring & detection — the buoy network above, (3) dissemination & communication, and (4) response capability. This sim models pillars 3–4 as one latency τ:

Lead time delivered = max(0, T_landfall − T_alert − τ)

Evacuated fraction = 1 / (1 + e^-((L − L50) / k))   (logistic response curve)

Even a perfect detector delivers zero useful lead time if τ (dissemination + evacuation mobilization) eats the whole warning window — which is exactly why real EWS programs invest as much in the "last mile" (sirens, cell alerts, evacuation drills) as in the sensors themselves.

Detection threshold — how strong the averaged signal must be before an alert is issued.
Buoy network size — more independent sensors reduce noise, making detection faster and false alarms rarer at the same threshold.
Dissemination & response latency — minutes lost between alert and public action; subtracted straight from lead time.
Storm approach window — total minutes available from storm formation to landfall, the whole budget the warning chain has to work with.

Buoy below threshold Buoy near threshold Buoy over threshold Evacuating residents

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