Verisk Severe Thunderstorm Model for the United States

Enhancements to the Verisk Severe Thunderstorm Model for the United States

Scope

The Verisk Severe Thunderstorm Model for the United States has been updated to incorporate new data, and research innovations as well as framework enhancements and adjustments to the interpretation of observational data. This includes updates to the hazard and vulnerability modules as well as changes to the stochastic event set definitions.

General model updates

Hazard

  • The updated hazard model represents present-day climate conditions.
    • Trends in hail frequency and intensity
    • Incorporates latest data (2018-2023)
  • All sub-perils
    • New observational data through 2023
  • Hail
    • Improved physical representation of hail events, including hail frequency and improvements to hail swath placement in areas of sharp elevation transitions.

Vulnerability

  • All sub-perils
    • New support for solar farms (Touchstone)
    • Updated building damage functions, including
      • Unknown year built, based on updated age distributions
      • Unknown primary features, based on the updated Industry Exposure Database
    • Updated infrastructure damage functions
  • Hail
    • Enhancements to roof aging based on recent research, including roof covering-specific aging and deterioration impacts
    • Updates to the hail performance of hurricane wind-rated roof covering feature, resulting in smoother hail loss cost across states
    • Updated building damage functions across all supported risk types
  • Wind and tornado
    • Yearly adjustments that account for roof aging and deterioration
    • 10-year roof aging bins updated, current as of 2025
    • Updated manufactured homes damage functions for commercial risks
    • Updated large industrial facilities damage functions (Touchstone)
Catalogs and event sets
  • Stochastic catalog(s)
    • Redefined catalogs (Baseline, Expanded Events)
      • The Baseline catalog includes significant loss events defined using both country-wide and state-specific loss criteria. The Baseline catalog is the smaller of the two catalogs.
      • The Expanded Events catalog includes all events from the Baseline catalog and additional events that do not exceed the Baseline loss thresholds but do meet the meteorological criteria defined for this model. This catalog is the larger of the two catalogs.
    • New catalogs (events regenerated)
      • Touchstone
        • 10,000-year Baseline
        • 10,000-year Expanded Events
        • 50,000-year Baseline
        • 50,000-year Expanded Events
        • 100,000-year Baseline
        • 100,000-year Expanded Events
      • Touchstone Re
        • 10,000-year Baseline
      • All event IDs are new.
  • The U.S. historical event catalog has been updated to include two new historical events: Ida 2021 (event ID 123) and Ian 2022 (event ID 124).

Touchstone-specific updates

  • Support for additional construction and occupancy codes
    • Construction: Updated to 168 classes (including 20 marine asset and 8 solar classes)
    • Occupancy: Updated to 130 classes (including 62 large industrial facility, 12 marine storage, and 6 solar)
  • New solar farm construction and occupancy codes are the first of several enhancements that will ultimately provide support for renewable energy assets for U.S. models. Currently available only for the Verisk Severe Thunderstorm Model for the United States.
    • New construction and occupancy classes
      Table 1. New construction codes for solar exposures
      Construction code Category Description
      500 Solar, Rooftop (unknown anchorage) Panels on flat or pitched roof, unknown mount.
      501 Solar, Rooftop, Anchored Panels attached to the roof using anchors. Typically these are mounted on a pitched roof at the same angle as the pitch of the roof.
      502 Solar, Rooftop, Ballasted Panels mounted on flat roof using ballasts. Typically these are mounted at a fixed angle.
      510 Solar Ground Mounted (on tracker or fixed) Panels on unknown mount type.
      511 Solar Ground Mounted, Single Axis Panels move on one axis, typically to track sun east to west.
      512 Solar Ground Mounted, Dual Axis Panels move on two axes, typically to track sun east to west at a range of altitudes.
      513 Solar Ground Mounted, Fixed Tilt Panels on a ground-level racking system at a fixed angle.
      514 BESS (Battery Energy Storage System) Battery system for ground-mounted solar installations, any occupancy.
      Table 2. New occupancy codes for solar exposures
      Occupation code Category Description
      3001 Residential Solar Energy Risk Residential assets
      3011 Commercial Solar Energy Risk Commercial assets
      3020 Utility Solar Unknown Utility-scale assets with capacity unknown
      3021 Utility Solar Small Energy Risk Utility-scale assets with capacity under 5 megawatts (MW)
      3022 Utility Solar Medium Energy Risk Utility-scale assets with capacity between five MW and 25 MW
      3023 Utility Solar Large Energy Risk Utility-scale assets with capacity above 25 MW
    • Over 70 damage functions (coverages A and D combined) for all U.S. severe thunderstorm sub-perils (hail, straight-line wind, and tornado) for solar construction/occupancy classes.
    • Note: Solar support does not include height and age characteristics.
  • Updated large industrial facility damage functions
  • Updated marine damage functions
  • Updated Secondary Risk Characteristics
    • All perils: Updated impacts for aging and deterioration for both building and roof
    • Hail: Updates to
      • Roof covering
      • Roof year built

Touchstone Re-specific updates

  • Industry losses are included for baseline events in the Touchstone Re ILF. The additional events in the expanded catalog will produce company losses in Touchstone Re if a CLF or CLA from detailed loss analysis in Touchstone produces loss for them.