The global livestock sector currently consumes about 33% of global water withdrawals, primarily for irrigation of feed crops. To understand how the livestock sector can potentially mitigate the impacts of its water use, two factors are critical. First, there are different types of water resources available in the landscape and each have markedly different impacts on the social-ecological landscapes in which they are consumed. Second, increased use of crops for animal feed causes greater competition for water use between the production of feed for animals and food for humans.
This thesis aims to improve our understanding of the effects of consumptive blue water (i.e. ground or surface water) and green water (i.e. soil moisture) in a landscape, and to develop and apply a method to better assess such effects of consumptive water use (CWU) associated with livestock production. We first identified differences in existing methods and developed a conceptual framework for assessing CWU of livestock that aim to address the aforementioned critical factors. This framework was subsequently applied to beef production systems in Brazil and Uruguay. We focused on CWU for animal feed production as this constitutes the vast majority of water demand in livestock systems and choose beef production since beef cattle can be fed entirely on pastures or on a mixture of pastures and crops.
Results from this thesis confirm the importance of considering both blue and green water resources separately. Moreover, it argues that green water should be considered in regard to the land on which the water resources are used, e.g. cropland or grassland. We showed that the traditional measures of water use efficiency (i.e. litres of CWU per kg of beef produced) is lowest in extensive systems where cattle are fed on natural pastures, and increases if cattle are fed on improved pastures and with feed crops. Our newly developed water use ratio (WUR), however, showed that beef production systems that use high opportunity cost feeds, such as feed crops, can potentially contribute more human digestible proteins by growing food crops than by producing beef. Similarly, it was shown that by using low opportunity cost feeds, such as grass and by-products, livestock systems can have an important contribution to food and nutrition security while avoiding feed-food competition over land- and water resources. This thesis illustrates that there are multiple pathways to increase beef production without significantly increasing feed-food competition, and that low-opportunity cost feeds can effectively contribute to a sustainable development of the food sector in areas where resources are scarce.
It was concluded that estimates of water use in livestock value chains should distinguish between the different types of water, i.e. green and blue water and that the water use should be considered in a local context in order to identify potential impacts of CWU in the landscape. To address the impacts resulting from green CWU, green water use should always be categorised according to the land area and land use where it is consumed, for example on cropland or grasslands. This allows for an identification of alternative uses of that land and corresponding water resources and can contribute to more sustainable use of green water resources and the development of a sustainable food sector.