Cause-effect pathway

The impact model is addressing lack of water for agricultural food production and consequent effects on the Area of protection ‘Human Health ’ caused by water consumption.

Modeling approach

Two different methods are available: (1) marginal CFs, which are typically used in LCA to address impacts of additional water consumption (marginal change in water consumption rate) and (2) average CFs, which are used to assess total impacts of water consumption within a region and to characterize the impact of an activity proportionally to the impact of total water consumption.

Value choices

A number of choices have been made for the calculation of the characterization factors, namely:

• Time Horizon:The time horizon is infinite, assuming steady-state conditions. The effect of water consumption is described through competition for a renewable resource on annual level.

The choice of discounting:no discounting to future effects is applied

Excluded impact pathways:

• potential human health effects due to lack of water for drinking water purpose and hygiene are excluded due to low level of evidence of a cause-effect relation to water consumptio
• effect of decreased food production on international markets and consequent effects in other countries through increased prices in globalized markets are excluded due to low level of robustness and moderate level of evidence.

Spatial variability

The method was applied to >11'000 watersheds with varying sizes, with global coverage. Country-average characterisation factors 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) is:

CFMN,i= WSIi·WU%A,i·HDFi·WRMN-1·DFMN
WDFi= WSIi·WU%A,i
EFi= HDFi·WRMN-1

where CFMN,_i [DALY/m³_consumed] is the expected specific damage per unit of water consumed in watershed i (as specified in the LCI-phase), WDF_i is the water deprivation factor [m³/m³], EF_i is the effect factor [cases·yr/m3], WSI_i is the water stress index[-], WU_%A,i is the share of water used in agriculture[-], WDF_i is the human development factor [-], WR_MN is the minimum water requirements for personal food provision [m³/(cases·yr)] and DF_MN the damage factor [DALY/(yr·case)].