ARI · Climatology

Aridity Index

UNEP P/PET aridity index from the drought v2 climate chain (Thornthwaite PET) · v0.1 · 2026-07

The UNEP aridity index (P/PET) from 85 years of ERA5 climatology — hyper-arid through humid on one dimensionless scale, with a per-pixel confidence interval. A byproduct of the drought v2 hazard chain, shipped at honest ERA5-native resolution. The whole bundle is ~2 MB.

Global P/PET aridity index — 85-year ERA5 climatology, native 0.25°

What ships in the bundle

3 global ~0.25° (~28 km, ERA5 native) GeoTIFFs (~2 MB total) plus the full documentation set. All files are Cloud-Optimized GeoTIFFs with internal tiling and overviews — fast for both bulk download and windowed reads.

FileDtypeUnitsDescription

aridity_index_0p25deg_90m.tifuint16 (SCALE)P/PETUNEP aridity index (dimensionless)

aridity_class_0p25deg_90m.tifuint8class 1–6UNEP class: hyper-arid → humid

aridity_index_ci_0p25deg_90m.tifuint16 (SCALE)P/PET90% confidence-interval half-width

Note: filenames carry a legacy _90m suffix; the native grid resolution for this Layer is ~0.25° (~28 km, ERA5 native).

Method

Inputs · ERA5 monthly precipitation + 2m temperature 1940-2024 (85-year climatology)

Training labels · —

Method · UNEP P/PET aridity index from the drought v2 climate chain (Thornthwaite PET)

Documentation

Download

Free for non-commercial use. Account required.

# $PETREL_API_KEY = your API key (tlk.…) from the dashboard — free tier works.

# 1. Fetch 1-hour signed URLs for every file in the bundle:
curl -s -H "X-API-Key: $PETREL_API_KEY" \
  https://api.petreldata.io/v1/layer/aridity/v0.1/bundle > bundle.json

# 2. Download the full layer (~2 MB):
mkdir -p aridity_v0.1
jq -r '.files[] | [.url, .name] | @tsv' bundle.json | \
  while IFS=$'\t' read -r url name; do
    curl -s "$url" -o "aridity_v0.1/$name"
  done

License & citation

License: CC-BY-NC-4.0. Free for academic, research, and other non-commercial use. For commercial licensing, contact licensing@petreldata.io.

Citation:

Petrel (2026). Petrel Aridity Index v0.1.
https://petreldata.io/layers/aridity
CC-BY-NC-4.0