Precipitation of driest month — 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 how much rainfall falls in the driest month of a typical year, averaged over the 1981-2010 reference period. It is a bioclimatic indicator describing the depth of the seasonal dry period, which shapes water availability, vegetation stress and the suitability of land for different crops and ecosystems.

How it is built

The layer comes from CHELSA-CMIP6 v2.1, a high-resolution global climatology developed by Karger and colleagues. The measured variable is the precipitation total of the driest calendar month, derived from the 1981-2010 baseline climate record. It is presented as a reference climatology on a fine global grid of roughly 2 km, making it considerably more detailed than typical coarse climate datasets.

How to read it

Higher values indicate wetter conditions even in the driest month — a milder dry season; lower values indicate more pronounced seasonal drought, with the driest month receiving very little rain. As a baseline layer it describes recent historical climate and is best read alongside the matching future-projection variant.

Class thresholds

The underlying layer models a physical flux: precipitation of the driest month, in millimetres (mm) — the rainfall total of the driest calendar month of a typical year. It is rendered as a continuous colour ramp over the range 0 to 200 mm rather than as discrete risk classes, so there is no break table and the layer carries no proximity trigger (it is contextual and does not raise a risk flag on its own).

How these thresholds were set. There are no risk-class breaks: the quantity is a raw CHELSA bioclimatic variable shown on a continuous scale. The 0–200 mm display range is a Darwin in-house rendering choice, not a published CHELSA classification.

Reference: CHELSA-CMIP6 v2.1 (Karger et al.) — chelsa-climate.org.

Source

CHELSA-CMIP6 v2.1 (Karger et al.), 1981-2010 reference climatology; open licence.

Comparison with the WWF Risk Filter Suite

The WWF Risk Filter Suite does not publish standalone bioclimatic precipitation variables of this kind. This baseline CHELSA layer is a climate-descriptor extension rather than a WWF risk indicator, so it has no direct equivalent in the WWF methodology.

Legend

Symbolised field: Precipitation of driest month

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