Aug 10, 2020 Iowa Derecho — Wind Damage

Straight-Line Wind (SLW) Vulnerability Model

Per-building wind damage probability computed using Hazus Hurricane Technical Manual v7 lognormal fragility curves for four construction classes.

Algorithm

1. Peak gust observations from IEM ASOS (hourly METARs) and SPC Local Storm Reports (LSR) are merged into a point observation set.
2. IDW interpolation (power p=2, global — all observations used) assigns peak_gust_mph to each building centroid.
3. Hazus lognormal fragility: P(DS ≥ ds | v) = Φ[(ln v − λ_ds) / ζ] for each damage state (Slight → Complete).
4. Mean Damage Ratio = Σ P(ds_i) × CDFactor_i where CDFactors: Slight=0.02, Moderate=0.10, Extensive=0.50, Complete=1.00.
5. ground_up_loss = MDR × RCV (footprint_sqft × $150/sqft — full structure, wind is whole-structure peril).

Fragility Parameters (W1 — Light Wood Frame)

Calibration

Event Type Multipliers

References