Water Scarcity - Blue Water Scarcity

Blue Water Scarcity estimates how much of the available freshwater in a region is used and not returned to the environment (consumption). Water consumption is not solely modelled, but based on historical national water footprint data.

Overview

Data Type	Modelled based on historic water footprint data and observed and modelled water balance data
Source	Mekonnen & Hoekstra (2016)
Spatial Resolution	Spatially explicit to river basins (HydroBASINS level 6)
Temporal Resolution	Based on data for the years 1996-2005. Official updates to be confirmed.
Interpretation	The Blue Water Scarcity score translates the raw values (%) into a 0-10 risk categorization based thresholds established by scientific literature.
Concern Level	Very Low = Score 0 - 2 Low = Score 2 - 4 Moderate = Score 4 - 6 High = Score 6 - 8 Very High = 8 - 10
Framework Relevance	Blue Water Scarcity is relevant under CSRD (ESRS E2 and ESRS E3) as well as under TNFD and SBTN.

Detailed Specifications

Explanation

Analogously to the Water Depletion indicator, Blue Water Scarcity measures the ratio of the consumption of fresh surface water and groundwater (blue water footprint) to total blue water availability. Blue water refers to the water available in rivers, lakes and aquifers (green water = the water in soil and plants; grey water = human-caused waste water). The blue water footprints for this indicator are based on historic data on monthly national water footprint accounts from Mekonnen & Hoekstra (2011). The blue water availability is calculated as the sum of the runoff (i.e. the movement of water from rain, snowmelt, or other sources across the land surface) generated within an area plus remaining runoff generated in upstream areas.

Transformation & Interpretation

The raw Blue Water Scarcity values are expressed as percentages. The following thresholds are used to convert raw values into scores and concern levels analogously to Camargo et al. (2023):

Raw Values (%)	Score	Concern Level
≤ 20%	0 - 2	Very Low
20% - 100%	2 - 4	Low
100% -200%	4 - 6	Moderate
200% - 500%	6 - 8	High
> 500%	8 - 10	Very High

Source

The Blue Water Scarcity value provided as part of SBTN’s Water Availability Risk layer is sourced from Mekonnen & Hoekstra (2016).

Date of publication

2023 (2016)

Confidence & Accuracy

Medium (best available at global scale). The Blue Water Scarcity indicator is based on historic water footprint data and global hydrological modeling. The indicator might thus fail to accurately estimate water depletion levels at a local scale and representing current condition. However, the Blue Water Scarcity Indicator is science-based, peer-reviewed and explicitly required for science-based target setting under SBTN.

Relevance for CSRD

CSRD requires companies to identify operational sites situated in areas of water risk, incl. areas of high-water stress. The Blue Water Scarcity indicator is relevant under:

ESRS Article	Disclosure or application requirement
ESRS E2 AR 23 (c)	percentage of emissions of pollutants to water and soil occurring in areas at water risk, including areas of high-water stress
ESRS E3 DR 12 (c)	commitment to reduce material water consumption in areas at water risk
ESRS E3 DR 13	policy for sites located in an area of high-water stress
ESRS E3 DR 19	actions and resources in relation to areas at water risk, including areas of high-water stress
ESRS E3 DR 23 (a)	impacts, risks and opportunities related to areas at water risk, including improvement of the water quality
ESRS E3 DR 23 (c)	reduction targets for water consumption, in areas at water risk, including areas of high water-stress
ESRS E3 DR 28 (b)	total water consumption in m3 in areas at water risk, including areas of high-water stress
ESRS E3 AR 5 (b)	sites located in areas at water risk, including areas of high-water stress
ESRS E3 AR 13 (b)	risks including water quantity (water scarcity, water stress), water quality (...)

CSRD requires companies to consider and describe the data used in their analysis (ESRS E4 AR 27). For convenience, here a description of for the relevant criteria:

ESRS Data Criteria	Comment
(a) methodology, reason for selection, assumptions, limitations & uncertainties	Methodology: Blue Water Scarcity is estimated based on a global hydrological model including historic data on monthly national water footprint accounts. Reason for selection: The indicator has been selected to assess the level of water scarcity. The selected metric is science-based, peer-reviewed, widely used and specifically endorsed by SBTN guidelines. Assumptions: The indicator is model based and incorporates several assumptions detailed in Mekonnen & Hoekstra (2016). Limitations & uncertainties: The Blue Water Scarcity indicator is based based on historic water footprint data and global hydrological modeling. The indicator might thus fail to accurately estimate water depletion levels at a local scale and representing current condition.
(b) scope of metric	The Blue Water Scarcity indicator is applied at site level.
(c) biodiversity component of metric	The Blue Water Scarcity is an ecosystem-level nature indicator. It assesses ecosystem structure by providing an indicator for the physical state of the ecosystem.
(d) covered geographies	The Blue Water Scarcity indicator has global coverage.
(e) integration of ecological thresholds	The Blue Water Scarcity indicator relates to the planetary boundaries of freshwater change.
(f) frequency of monitoring, baseline condition and period	The Blue Water Scarcity indicator is based on data for the years 1996-2005. Official updates of the indicator remain to be confirmed.
(g) data type (primary, secondary, modelled, expert judgement	The Blue Water Scarcity indicator relies on modelled data.

Relevance for TNFD

The Blue Water Scarcity indicator is a suitable indicator to estimate water availability under the criteria of Physical Water Risk within TNFD’s LOCATE step.

Relevance for SBTN

The Blue Water Scarcity indicator represents one out of three water availability indicators explicitly required to use as a pressure-sensitive State of Nature indicator in SBTN Step1: Assess and Step 2: Interpret & Prioritize.

SBTN Data & Tool Criteria	Evaluation	Comment
Relevance	✅	Blue Water Scarcity contributes to the pressure-sensitive state of nature metric water availability required by SBTN methodology.
Representative	✅	Blue Water Scarcitydata represents a close fit with the SBTN characterization of the water availability issue and is appropriate to be applied under Step 1 & 2.
Spatial and Temporal Resolution	✅	The Blue Water Scarcityindicator is provided at the spatial resolution of 30-arc-minutes (~55km x 55km at equator). The indicator is based on blue water footprint data for the years 1996-2005.
Stability and Preservation	✅	Blue Water Scarcity data sets are likely to be maintained and preserved long-term as they are provided by SBTN.
Accessibility	✅	The Blue Water Scarcity is accessible upon request to the authors.
Interpretability	✅	The Blue Water Scarcity indicator is sufficiently interpretable and generates an appropriate input for the SBTN methodology.
Coverage	✅	Blue Water Scarcity has global coverage.
Authoritative and Accurate	✅	Blue Water Scarcity data is science-based, peer-reviewed and explicitly required by SBTN.