To whom it may concern
The report is quite an impressive work. However, I agree with previous comments, that it is trying to cover everything at the expense of covering the details as well as providing a consistent report.
I will focus my comments on the environmental assessment and footprint of water consumption for ensuring food security.
Especially the chapter 2.5.1 is very biased and does not account for international consensus finding and discussions around the water footprint concept. For instance the new ISO norm on water footprint is in contradiction to the concepts described here (ISO 14046). This reflects the discussion in scientific community that provide more insights into water footprint assessment, that are relevant for assessing environmental issues of water consumption. Some studies are:
Pfister S, Ridoutt BG (2013) Water Footprint: Pitfalls on Common Ground. Environmental Science & Technology 48:4-4 doi:10.1021/es405340a
- Pfister, S. and Hellweg, S. (2009). The water "shoesize" vs. footprint of bioenergy (Letter). Proceedings of the National Academy of Sciences of the USA, 106:E93-E94; doi:10.1073/pnas.0908069106
- Ridoutt, BG. and Pfister, S. (2010). A revised approach to water footprinting to make transparent the impacts of consumption and production on global freshwater scarcity. Global Environmental Change, 2010, 20(1), 113–120
- Pfister, S.; Bayer, P.; Koehler, A.; Hellweg, S. (2011). Environmental impacts of water use in global crop production: hotspots and trade-offs with land use. Environmental Science and Technology, 2011, 45(13), 5761–5768
These papers discuss the relevance of the location of water use, since water used in arid places is more relevant than that used in water-abundant places. Furthermore, combination of green and blue water is not making sense from a water resource perspective, but rather within the virtual water concept (showing how much water can be saved by imports). However, Water footprint tries to account for impacts.
Furthermore the combination with grey water is very strange, since dilution volumes without physical meaning are combined with water volumes. This text should be revised to account for the shortcomings of the presented method and provide solutions to this provided in scientific literature.
Furthermore, the temporal timing of water consumption is a key issue too, which has been accounted for by Mekonnen and Hoekstra 2011 in the blue water scarcity index and further elaborated in Pfister and Bayer 2013 (monthly water stress).
Due to the above mentioned critical issues, the presented numbers for water footprint are not indicating the pressure on water resources. Beef produced in Swiss alpine grassland is almost free of any water (could be ~100 liter per kg) consumption and therefore of much lower water footprint than protein from irrigated crops! The presented numbers must be put in context and also the uncertainty and spatial variability must be mentioned (compare above references).
Beyond this, more holistic approaches such as LCA, combining different environmental aspects might be added to avoid trade-offs between water consumption and pollution with more advanced methods for pollution assessment.
Kind regards
Dr. Stephan Pfister
Senior Research Associate
ETH Zurich, Switzerland
Stephan Pfister