Baseline Water Stress

Definition:

\(BWS\) is measured as the ratio of human water demand to water availability. The impact to the environment is considered implicitly by setting conservative thresholds of water scarcity. Perhaps, it is a water stress indicator most widely used in water risk assessment platforms, including AQUEDUCT, Water Risk Filter, and many others.

Interpretation:

A higher ratio likely corresponds to higher depletion of surface and groundwater resources and more competition amongst users, as well as the associated impacts on the environment and ecosystem functions.

Calculation:

Temporal accumulation: Long-term annual average from 2008 to 2020

Spatial unit: Basin

The calculation method of the \(BWS\) is updated with each version of AQUEDUCT, and here we followed the definition of the latest version, version 4.0. However, due to differences in the simulation settings of the underlying global water cycle model, the approach used to smooth water resources and water demand differs from that employed by AQUEDUCT.

The Baseline Water Stress of spatial unit \(b\) is calculated as

\begin{align} \ & BWS_{m,b}=\min(1,\max(0,\frac{\overline{WW}_{m,b}}{\overline{WA}_{m,b}})) \\ \ & BWS_b[\%]=\frac{\sum_{m=1}^{12}\overline{WW}_{m,b}BWS_{m,b}}{\overline{WW}_b}\times 100 \\ \end{align}

where \(\overline{WW}_{m,b}\) is the long-term mean monthly human water demand in month \(m\) and \(\overline{WA}_{m,b}\) is the long-term mean monthly water availability of spatial unit \(b\) in month \(m\). The \(\overline{WA}_{m,b}\) includes renewable freshwater resources and desalinated water produced.

The \(BWS\) index provided on the Water Security Compass was calculated using the postprocessed outputs of the H08 Japan version model.

Reference:

Kuzma S. et al., 2023. “Aqueduct 4.0: Updated decision-relevant global water risk indicators.” Technical note. Washington, DC: World Resources Institute. DOI