Hailstorm Climatology
This layer maps the long-term frequency of hailstorms around the world.
Source: NASA PMHC (TRMM+GPM) Year: 1998-2025 Category: Physical risks · Mitigating services · Climate Acute Risks Coverage: Global Format: Raster grid (~200 km) Used in risk analysis: Yes — gates Mitigating services
What it shows
This layer maps the long-term frequency of hailstorms around the world. It indicates where hail occurs most often, which is relevant for nature- and asset-related risk because hail can damage crops, infrastructure (roofing, vehicles, solar panels) and threaten human safety.
How it is built
The layer is based on NASA's Passive Microwave Hail Climatology, which infers hail occurrence from satellite observations. It combines records from the TRMM mission (1998–2014) and the GPM mission (2014–2025) at a coarse, roughly 200 km grid. The combined observations are normalised into a single hail-density measure, so that each cell expresses relative hailstorm frequency over the multi-decade period rather than an absolute count.
How to read it
Higher values indicate more frequent hailstorm occurrence; lower values indicate areas where hail is rare. Because the grid is coarse, the layer is best read as a broad climatological signal of hail-prone regions rather than a precise local hazard estimate.
Class thresholds
The underlying quantity is a physical hazard measure: normalized hail density from NASA's Passive Microwave Hail Climatology (PMHC) — a dimensionless index of relative hailstorm frequency over 1998–2025. The values are normalised, so they express relative frequency rather than an absolute number of hail days; higher means more frequent hail. The five classes map to the following thresholds on that index:
| Class | Normalized hail density |
|---|---|
| Very low | < 0.05 |
| Low | 0.05 – 0.35 |
| Moderate | 0.35 – 0.8 |
| High | 0.8 – 2.8 |
| Very high | ≥ 2.8 |
A site is flagged on the Mitigating services dimension when the layer value reaches 0.8 or above (the High class).
How these thresholds were set. The hail-density values themselves come unchanged from NASA PMHC (Bang & Cecil 2019). The five-class split (0.05 / 0.35 / 0.8 / 2.8) is a Darwin in-house classification of that surface — graded bins chosen to separate hail-prone from hail-rare regions — not a published NASA threshold set.
Reference: NASA Passive Microwave Hail Climatology — Bang & Cecil (2019).
Source
NASA Passive Microwave Hail Climatology (PMHC) — Bang & Cecil (2019), combining TRMM and GPM satellite observations.
Comparison with the WWF Risk Filter Suite
There is no equivalent indicator in the WWF Risk Filter Suite. Hail is a geophysical / acute-weather hazard rather than a biodiversity or water risk, so it sits outside the WWF methodology. This layer is a Darwin extension that broadens physical-hazard screening.
Risk analysis
A site is flagged on a dimension by combining a proximity trigger (this layer) with an activity trigger (the entity's ENCORE pressure/service). Proximity only → Potentially material; proximity and the matching ENCORE pressure/service is material → Very material; neither → Not material.
| Dimension | ENCORE service / pressure | Proximity trigger (this layer) | Activity trigger (entity) |
|---|---|---|---|
| Mitigating services | Hailstorm | Layer value above 0.8 | — |
Legend
Symbolised field: Hailstorm frequency (NASA PMHC)
| Value (Hailstorm frequency (NASA PMHC)) | Label | Colour |
|---|---|---|
| 0 | 1 - Very low (<0.05) | #ffffcc |
| 0.05 | 2 - Low (0.05–0.35) | #c7e9b4 |
| 0.35 | 3 - Moderate (0.35–0.8) | #7fcdbb |
| 0.8 | 4 - High (0.8–2.8) | #fd8d3c |
| 2.8 | 5 - Very high (>2.8) | #e31a1c |
Generated from darwin/layers/layer-hailstorm-climatology.toml and risk_indicator_pairs.toml (develop).