a spatially differentiated life cycle impact assessment method

# Water stress

#### Ecosystem Quality

###### Water stress

Water use is crucial for food production, industrial processes and other human needs. At the same time can a lack of water damage natural aquatic and terrestrial ecosystems.

#### Cause-effect pathway

The impact model for impacts of a loss of wetland habitat area is addressing the impacts of a lack of water that leads to a change in available water volumes and hence habitat areas. The definition of wetlands used is the definition of the Ramsar Convention, which defines wetlands as waterbodies that are “areas of marsh, fen, peatland, or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish, or salt, including areas of marine water the depth of which at low tide does not exceed six metres” (Ramsar Convention 1994), however, we excluded the marine wetlands.

The impact model for terrestrial vascular plant species outside wetlands takes into account that it needs a certain land area to generate a volume of freshwater from precipitation for maintaining vegetation. A lack of this land will thus lead to a damage on the vascular plant species.

Both impact pathways are only relevant for the Area of protection ‘Ecosystem Quality’ caused by water consumption.

Cause-effect chain for modelling the potential loss of species due to water consumption in aquatic and riparian habitat.

Cause-effect chain for modelling the potential loss of species due to water consumption in terrestrial habitat.

#### Modeling approach

Only marginal CFs are available for both model pathways. The approach based on wetland biodiversity takes animal species into account, who are then harmonized to one final factor, as described in the framework chapter. We take vulnerability scores of the species into account, highlighting the fact that not all species show the same resilience towards anthropogenic impacts.

#### Value choices

There are no value choices regarding the time horizon. For core assessments, it is recommended to only use the values based on surface water consumption, since these are less uncertain. For extended CFs, both surface and groundwater consumption is taken into account.

#### Spatial variability

All characterization factors are available in a spatially differentiated manner, on a sub-watershed level with a resolution of 0.05° x 0.05°. Country-average CFs are available too. A global average is not considered meaningful but provided for background processes.

#### Characterisation factors

The equation for calculating the characterisation factor (CF) for wetlands and riparian habitats is:

$$\mathsf{CF_{end,i,t}=\frac{\sum_{i,k=1}^n {FF_{k,t}\cdot EF_{k,t}}}{S_t\cdot VS_t}}$$

where FFk,t is the fate factor of wetland k and taxonomic group t and EFk,t is the effect factor of wetland k and taxonomic group t. S and VS are the species richness and vulnerability score of taxonomic group t, respectively and are used to transform the species-equivalents to PDF again. Keep in mind that these are global extinctions.

The equation for calculating the characterisation factor (CF) for terrestrial habitats is:

$$\mathsf{CF_{end,w}=\frac{{FF_w\cdot EF_w}}{S_{plants}}}$$

where FFw is the average fate factor on a watershed basis and EFw is the effect factor on a watershed basis for vascular plants. S is the global species number of vascular plants. Due to unavailability of data VS was assumed to be 1 for plants.

###### References

Ramsar Convention. 1994. Convention on Wetlands of International Importance especially as Waterfowl Habitat. The Convention on Wetlands text, as amended in 1982 and 1987. Paris, Director, Office of International Standards and Legal Affairs; United Nations Educational, Scientific and Cultural Organization (UNESCO).