Annual precipitation — 1981-2010 (CHELSA)

Source: CHELSA-CMIP6 v2.1 (Karger et al.) Year: 1981-2010 Category: Physical risks · Mitigating services · Climate Chronic Risks · 1981-2010 Coverage: Global Format: Raster grid (~2 km) Used in risk analysis: No (contextual layer; not used in materiality scoring)

What it shows

This layer maps the average total annual precipitation for the 1981–2010 reference period. It provides a baseline picture of how wet or dry different areas have been across recent decades. Rainfall availability is a core determinant of ecosystem type, water resources and agricultural viability, so this baseline underpins water-related and chronic-climate risk screening.

How it is built

The source is the CHELSA high-resolution climatology (version 2.1), one of its standard bioclimatic measures. It describes total annual precipitation averaged over the 1981–2010 reference window, derived from globally downscaled climate data at roughly a 2 km grid. As a reference climatology, it represents observed historical conditions rather than a forecast.

How to read it

Values are precipitation totals: higher values mark wetter areas and lower values drier ones. The layer is best used as a baseline reference to interpret the matching future-projection layer and to characterise the moisture regime of a site.

Class thresholds

The underlying quantity is a physical variable: total annual precipitation, in millimetres per year (mm/yr), averaged over the 1981–2010 reference period. This is a continuous-gradient layer with no discrete risk classes — pixel values are the rainfall total itself, rendered on a smooth colour ramp spanning 0 to 3 000 mm/yr (the display range; wetter sites exceed the upper end and the underlying data is not clipped to it). There is no risk-flag threshold: the layer is contextual and is not used in materiality scoring.

How these thresholds were set. There are no class breaks to set — the colour ramp is a Darwin in-house display choice (a linear stretch over the 0–3 000 mm/yr range that covers most land), not a classification. The precipitation values themselves come unchanged from the CHELSA-CMIP6 v2.1 bioclimatic climatology.

Source

CHELSA-CMIP6 version 2.1 (Karger et al.), open licence.

Comparison with the WWF Risk Filter Suite

There is no equivalent indicator in the WWF Risk Filter Suite. The WWF Suite publishes present-day risk indicators rather than baseline bioclimatic precipitation surfaces, so this is a Darwin reference-climatology layer supporting the chronic-climate theme and comparison with forward-looking projections.

Legend

Symbolised field: Annual precipitation

Generated from darwin/layers/layer-chelsa-precip_annual-historical.toml and risk_indicator_pairs.toml (develop).