6.8.2 — Multi-Hazard Warning Systems — maturity: live

Cascading Risk Modelling

Using multi-source satellite observation to model how one hazard triggers the next — flood undermines slope, slope fails, debris blocks river, river backs up into city.

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Disasters rarely arrive alone. An earthquake loosens hillside material; three days of rain saturate it; the resulting landslide dams a river whose backwater inundates a town that has already lost its power grid. National emergency managers who model only single-hazard events are planning for the wrong disaster. Satellite data — radar-derived soil-moisture, InSAR surface-deformation, optical flood extent, thermal anomaly mapping — gives the continuous, wide-area observational thread that lets a cascading risk model update itself as the chain unfolds rather than being run once as a static pre-event estimate.

The satellite stack required is deliberately heterogeneous. C-band SAR provides all-weather flood and landslide mapping at 5–10 m resolution. InSAR time-series (Sentinel-1 cadence or better) tracks precursor ground deformation in the hours to days before a mass-movement event. Multispectral imagery captures post-event land-cover change and infrastructure damage. Medium-resolution thermal data flags wildfire ignition that a flood-weakened, debris-laden watershed can spread further than pre-disaster fuel models predict. No single commercial vendor provides this combination under a single sovereign access agreement, which is precisely the problem.

The operational output is a continuously updating probabilistic risk graph — nodes are hazard states, edges are conditional trigger probabilities — delivered to the national emergency operations centre before and during a multi-hazard event. Response commanders can see not just where the current hazard is, but which downstream nodes are about to light up and how long the window is before they do. That foresight shifts resource pre-positioning from reactive to anticipatory, directly reducing casualties and infrastructure loss in a disaster sequence that would otherwise overwhelm reactive coordination.

What matters

Cascading sequences cause disproportionate casualties: the 2018 Palu, Indonesia earthquake-tsunami-liquefaction chain killed over 4,000 people, a toll dominated by the third-order hazard that static models missed.
InSAR deformation time-series can detect precursor slope instability at centimetre scale days before failure — but only if the national operator has persistent, uninterrupted tasking authority over the relevant orbit track.
Commercial data-access agreements routinely exclude priority tasking during declared foreign disasters, precisely when cascading risk model inputs are most urgently needed.
Multi-hazard risk chains cross ministry boundaries; only a sovereign platform with a single data authority can enforce real-time data fusion across meteorology, geology, hydrology and civil protection feeds without inter-agency licensing friction.

Sovereignty score: 9/10 — Cascading risk modelling depends on uninterrupted, priority access to heterogeneous satellite feeds at the exact moment a foreign vendor is most likely to ration or deny them — sovereign ownership is the only operationally reliable solution.

Commercial priority-tasking agreements contain force-majeure and national-security carve-outs that allow vendors to redirect capacity during large-scale disasters, removing access precisely when cascading risk inputs are most critical for national emergency decision-making.
Export-control regimes (US EAR, EU dual-use regulation) can restrict delivery of high-resolution SAR and InSAR products to certain nations or during certain geopolitical periods, breaking the continuous data thread that cascading risk models require to remain calibrated.
Cascading risk model outputs inform decisions to evacuate cities, shut down nuclear or hydro infrastructure, and pre-position military assets — their classification, integrity and dissemination must be controlled by national civil protection and defence authorities, not third-party platforms with foreign legal exposure.
Multi-hazard chains evolve faster than procurement cycles: a sovereign operator can retask satellites, adjust revisit geometry and fuse new data streams within hours; a nation dependent on commercial subscriptions must re-negotiate terms while the cascade is already propagating.

Reference architecture

Payload: Primary: C-band SAR, 5m stripmap and 20m ScanSAR modes, 250km swath in wide-area mode for flood and landslide mapping. Secondary: multispectral imager, 10m resolution, 8 bands including NIR and SWIR for land-cover change and burn-scar mapping. Optional augmentation: GNSS-RO receiver for atmospheric profiling to feed precipitation cascade triggers.
Bus class: ESPA-class microsat, 150–200kg per SAR unit; 6U–16U cubesat for the multispectral and GNSS-RO auxiliary nodes. Mixed-class constellation keeps per-unit cost low while maintaining the payload diversity cascading risk models require.
Orbit: Sun-synchronous LEO at 520–560km, dual-plane 8-satellite SAR constellation providing 4–6 hour revisit over national territory; 12-satellite multispectral constellation in complementary planes. InSAR coherence requires consistent repeat-pass geometry, so orbital maintenance budget must hold ground-track repeat to within ±1km.
Ground segment: 3-station national network (X-band SAR downlink, S-band TT&C) co-located with national meteorological and seismological network nodes to minimise new infrastructure cost; SatNOGS-compatible UHF/VHF backup for housekeeping telemetry. Direct injection into the national emergency operations centre data bus via fibre.
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References

UNDRR — Sendai Framework and Multi-Hazard Risk Assessment Guidance — The Sendai Framework explicitly calls for multi-hazard risk assessment as the foundation of national disaster risk reduction strategies. UNDRR guidance defines cascading events as a distinct category requiring dedicated modelling approaches beyond single-hazard methods.
ESA — Sentinel-1 SAR for Disaster Response — Sentinel-1's C-band SAR provides all-weather, day-night imaging used operationally for flood mapping, landslide detection and ground deformation monitoring. ESA's Copernicus Emergency Management Service activates Sentinel-1 rapid mapping within hours of major events.
USGS — Landslide Hazards Program: Post-Wildfire and Post-Earthquake Debris Flow Research — USGS documents how post-wildfire and post-earthquake landscapes exhibit dramatically elevated debris-flow susceptibility, a canonical cascading hazard chain. The programme provides empirical trigger thresholds used in operational cascading risk models.
NASA — ARIA Project: Advanced Rapid Imaging and Analysis for Disasters — NASA JPL's ARIA team demonstrates automated production of damage proxy maps and flood extent products from SAR data within 12–24 hours of major events. The pipeline architecture is openly documented and adaptable to sovereign constellation operations.
ICEYE — Persistent Monitoring and Rapid Tasking for Disaster Response — ICEYE's SAR constellation illustrates the commercial state-of-the-art for rapid flood and damage mapping, with sub-hourly revisit in some geometries. Its commercial pricing and export-control status make it a reference benchmark rather than a strategic dependency for sovereign cascading risk programmes.