cff-version: 1.2.0
title: "Petrel Aridity Index Layer v0.1 Global ML"
message: "If you use this dataset, please cite it as below."
type: dataset
authors:
  - name: "Petrel"
    website: "https://petreldata.io"
date-released: "2026-07-10"
version: "v0.1-global-ml"
license: "CC-BY-NC-4.0"
url: "https://petreldata.io/layers/aridity/v0.1"
keywords:
  - "aridity"
  - "aridity index"
  - "P/PET"
  - "potential evapotranspiration"
  - "drought"
  - "desertification"
  - "UNEP"
  - "climate classification"
  - "global"
abstract: >
  Global long-term aridity dataset at native ~28 km (0.25°) resolution, in
  three rasters: the continuous aridity index P/PET (long-term mean
  precipitation over Thornthwaite potential evapotranspiration, ERA5
  1940-2024); the UNEP five-class classification (hyper-arid, arid,
  semi-arid, dry-subhumid, humid; Middleton & Thomas 1997 thresholds);
  and a 90% block-bootstrap confidence-interval half-width on the index.
  Coast-clipped to the GSHHG full-resolution shoreline; Antarctica
  excluded. A byproduct of the Petrel drought v2 ERA5 pipeline. v0.1 uses
  temperature-only Thornthwaite PET to span the full 85-year record and is
  qualitatively checked against the CGIAR-CSI Global Aridity Index;
  quantitative validation and a Penman-Monteith variant are scheduled for
  v0.2.
references:
  - type: article
    authors:
      - family-names: "Hersbach"
        given-names: "Hans"
    title: "The ERA5 global reanalysis"
    year: 2020
    doi: "10.1002/qj.3803"
  - type: book
    authors:
      - family-names: "Middleton"
        given-names: "Nick"
      - family-names: "Thomas"
        given-names: "David"
    title: "World Atlas of Desertification, 2nd ed."
    year: 1997
  - type: article
    authors:
      - family-names: "Thornthwaite"
        given-names: "C. W."
    title: "An approach toward a rational classification of climate"
    year: 1948
    doi: "10.2307/210739"