Assessing water footprint and associated water scarcity indicators at different spatial scales : a case study of concrete manufacture in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master in Environmental Management, Massey University, Manawatu Campus, New Zealand

Abstract

Water scarcity is a growing issue of concern across the globe. In recent times a complex suite of water footprint impact assessment tools and concepts have supplemented traditional management approaches. There are several methods proposed in the literature to both quantify water use and assess its environmental impacts at defined spatial scales. In New Zealand, case studies in the water footprinting space are sparse, and are for the majority focused on the agricultural industry. This thesis focused on evaluation of different water footprint methods and their associated water scarcity indicators to assess water use impacts for the building and construction sector of New Zealand. The water footprints of 1 m³ ready mix concrete manufactured at 27 concrete batching plants throughout New Zealand were calculated at three distinct spatial scales: the freshwater management zone scale, catchment scale, and regional scale. Four water footprint characterisation factors (blue water scarcity (WSblue) (Hoekstra et al., 2011), water stress index (WSI) (Pfister et al., 2009), water depletion index (WDI) (Berger et al., 2014), and available water minus demand (AMD) (Boulay et al., 2016)) were used to assess the environmental impact of water use for 1 m³ ready mix concrete at the three spatial scales. The average volumetric blue water footprint of the 27 ready mix batching plants was quantified at 0.18 m3 (180 litres) of water per m³ of concrete, and ranged from 0.15 (150 litres) to 0.29 m³ (290 litres) of freshwater per m³ of concrete. For three of the four water footprint methods used (WDI, WSI and WSblue), and across the three spatial, the Ashburton boundary ranked highest in terms of the environmental impacts of a specified quantity of water use. In contrast, the AMD method ranked the Palmerston North boundary highest across the three spatial scales. At the freshwater management zone and catchment scales, the WDI, WSI and WSblue methods ranked the Wanganui area lowest, and the AMD method ranked the Greymouth area lowest. At the regional scale, all the four water footprint methods ranked the West Coast region lowest in terms of the environmental impact of water use, due mainly to the fact that the West Coast has more available water and a lower allocation demand than other regions studied. The analysis indicated that volumetric water use varied by a factor of two across the different plants (per m3 concrete). For three of the four WF methods (WDI, WSI and WSblue), the WF results were similar in their rankings of the different plants at all the geographical scales; however, the AMD method resulted in different rankings at all the geographical scales. Overall, the WDI and WSI water scarcity indices calculated by Berger et al. (2014) and Pfister et al. (2009) were less readily adaptable to the finer resolution in New Zealand. The WSblue and AMD calculated by Hoekstra et al. (2011) and Boulay et al. (2016) however, were found to be more readily adaptable. It is recommended that these methods be explored further with respect to their potential use at the finer resolution in New Zealand.