Water for food is one of the main global issues and irrigation is a limiting factor in agricultural production. Food supply is a vital human need and insufficient nutrition accounts for ~3% of overall global health impacts (WHO 2014) and further contributes to impacts form other diseases. While many factors contribute to this issue, reduced water availability caused by water consumption leads to reduced availability for food production and consequent yield losses.
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.
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.
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.
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.
The equation for calculating the characterisation factor (CF) is:
where CFMN,i [DALY/m3consumed] is the expected specific damage per unit of water consumed in watershed i (as specified in the LCI-phase), WDFi is the water deprivation factor [m3/m3], EFi is the effect factor [cases·yr/m3], WSIi is the water stress index[-], WU%A,i is the share of water used in agriculture[-], HDFi is the human development factor [-], WRMN is the minimum water requirements for personal food provision [m3/(cases·yr)] and DFMN the damage factor [DALY/(yr·case)].