Zoonotic disease spillover risk (global, Allen et al. 2017)

Source: Allen et al. (2017) Year: 2017 Category: Physical risks · Mitigating services · Biological hazards Coverage: Global (land only) Format: Raster grid (~5 km, aggregated from a ~100 km source) Used in risk analysis: Yes — gates Mitigating services

What it shows

This layer measures the relative risk that new infectious diseases will emerge by jumping from animals to humans (zoonotic spillover). Areas of higher risk tend to be where conditions favour the emergence of diseases such as COVID-type illnesses. It concerns diseases affecting people rather than agricultural pests, and helps flag locations where biological hazard is comparatively elevated.

How it is built

The layer is based on Allen et al. (2017), a published global model that predicts a relative-risk surface for emerging zoonotic diseases at roughly a 100 km grid, adjusted for differences in disease-reporting effort and for human population demographics. Following WWF rules, the underlying risk is summarised per river-basin unit (HydroBASINS Level 7 catchments), taking the maximum value within each, and basins are then grouped into five classes by their relative ranking. The classified result is presented as a finer global grid; oceans carry no value. It is intended as a screening layer.

How to read it

The layer uses a five-class scale: very low, low, moderate, high and very high. Higher classes indicate areas where the modelled likelihood of a new animal-to-human disease emerging is greater; lower classes indicate comparatively low risk. A site is assessed by the class of the area it falls within.

Class thresholds

The underlying quantity is a dimensionless relative-risk index for emerging zoonotic disease (Allen et al. 2017), modelled at ~100 km resolution and adjusted for disease-reporting effort and human population demographics. The index is summarised as the maximum value within each HydroBASINS Level 7 catchment, then binned into five relative (quantile-based) classes across the global set of catchments — so the class breaks are percentiles of the global distribution rather than absolute index cut-offs:

A site is flagged on the Mitigating services dimension when the layer reaches class 4 (High) or above (template: "High zoonotic-spillover risk zone (WWF class >= 4, Allen et al. 2017 EID surface)").

How these thresholds were set. The five-class split follows the WWF Biodiversity Risk Filter (BRF) methodology for the Disease indicator (S3_3): the per-catchment maxima of the Allen et al. (2017) relative-risk surface are ranked into WWF quantile classes (<50th / 50–75th / 75–90th / 90–95th / >95th). The breaks are therefore percentiles of the global distribution, set by the WWF BRF rule, and not absolute index values.

Reference: WWF Biodiversity Risk Filter — riskfilter.org/biodiversity.

Source

Allen, T. et al. (2017), "Global hotspots and correlates of emerging zoonotic diseases", Nature Communications 8:1124, doi.org/10.1038/s41467-017-00923-8. Aggregation units from HydroBASINS / HydroSHEDS (Lehner & Grill 2013, CC-BY).

Comparison with the WWF Risk Filter Suite

This layer maps to BRF S3_3 Disease and is aligned: it uses the same Allen et al. (2017) zoonotic-spillover surface that WWF references for this indicator.

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.

Legend

Symbolised field: Zoonotic spillover risk

Generated from darwin/layers/layer-zoonotic-spillover-global.toml and risk_indicator_pairs.toml (develop).