Freshwater Quantity Overshoot

Source: SBTN Freshwater Quantity Target v2 (Hogeboom et al.) Year: 2025 Category: Transition risks · Overexploitation Coverage: Global Format: Boundary polygons (sub-catchments) Used in risk analysis: Yes — gates Overexploitation

What it shows

This layer flags sub-catchments where freshwater is being used beyond what the local water system can sustainably provide. It identifies areas of water overuse, which is central to assessing water-related dependencies, transition risk and alignment with science-based water targets.

How it is built

The layer is based on the Science Based Targets Network's Freshwater Quantity Target (version 2), developed by Hogeboom and colleagues (2025). For each sub-catchment, annual blue-water consumption (water drawn from rivers, lakes and aquifers) is compared against a sustainable cap. Where consumption exceeds that cap — an overshoot greater than zero — the sub-catchment is flagged. The assessment is carried out over global sub-catchment units.

How to read it

This is a flag-based layer rather than a graded score: a sub-catchment is either in overshoot (sustainable freshwater use exceeded) or it is not. A site falling within a flagged sub-catchment should be treated as exposed to freshwater-quantity stress and reviewed further.

Class thresholds

The underlying quantity is a physical flux: annual blue-water consumption (water drawn from rivers, lakes and aquifers, in m³/year) compared against a sustainable cap (m³/year). The flag itself is binary — overshoot greater than zero — but the legend grades the overshoot by the water-consumption reduction needed to return within the cap, expressed as a percentage of consumption:

A site is flagged on the Overexploitation dimension when it falls within any overshoot sub-catchment (the layer intersection trigger; template: "Site located in a sub-catchment where blue water consumption exceeds the sustainable cap (SBTN FQT v2)"), provided the entity's matching ENCORE "Volume of water use" pressure is also material.

How these thresholds were set. The overshoot flag and the sustainable cap follow the Science Based Targets Network (SBTN) Freshwater Quantity Target v2 methodology (Hogeboom et al., 2025): a sub-catchment is in overshoot when consumption exceeds the science-based cap. The four reduction-target bands (1–25, 26–50, 51–75, 76–100%) are even 25-percentage-point quartile bins of the required reduction — a Darwin in-house presentation of the SBTN reduction target; the cap derivation itself is set in the SBTN methodology and is not reproduced in Darwin's configuration.

Reference: SBTN Freshwater Quantity Target v2 (2025), Hogeboom, Su, Prunes, Dilks & Townsend.

Source

SBTN Freshwater Quantity Target v2 (2025); Hogeboom, Su, Prunes, Dilks and Townsend (2025). Licensed under CC BY 4.0.

Comparison with the WWF Risk Filter Suite

This contributes to WWF Biodiversity Risk Filter indicator S1_1 Water Availability, specifically its freshwater-quantity dimension. It is aligned with the WWF water-availability family and adds a science-based-targets view of where freshwater use exceeds sustainable limits.

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: Water consumption reduction target

Generated from darwin/layers/layer-freshwater-quantity-overshoot.toml and risk_indicator_pairs.toml (develop).