Revised Approach to Water Footprinting

A revised water footprint method devised by Ridoutt and Pfister takes into consideration the type of water source and different usages during stages of production to determine how much Dolmio® pasta sauce and Peanut M&M’s® contribute to water scarcity (2009).  Existing water footprint calculations use the volumetric summation of all water content in the product at all stage of production and consumption. Under the existing method, the products Dolmio® pasta sauce and Peanut M&M’s® have water footprints of 202 and 1153, but the revised water footprints offer a drastically different relationship. The stress-weighted water footprints of Dolmio® pasta sauce and Peanut M&M’s® are 141 and 131. Winnie Wong

Ridoutt, B., 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 20, 113-120.

Bradley G. Ridoutt of the Australian Commonwealth Scientific and Research Organization and Stephan Pfister of the Swiss Federal Institute of Technology Zurich demonstrated a revised water footprint calculation method using brand products, Dolmio® pasta sauce and Peanut M&M’s®. Ridoutt disaggregates water according to the different sources: blue water which is surface and groundwater sources, and green water which is rainwater that is consumed through crop evapotranspiration. Because some places have a higher degree of water scarcity than others, location and level of stress imposed by different activities are considered in calculating a product’s water footprint. Therefore, the water consumption at specific locations at each point in the product life cycle and the water stress index (WSI) by Pfister (2009) were used to determine the level of contribution to water scarcity of both products.

In both cases of Dolmio® pasta sauce and Peanut M&M’s®, the agricultural stage of production contributed the greatest, followed by operations, ingredients processing and packaging. The study found that blue water sources are typically directly consumed at rates exceeding short-term replacement therefore processes heavily using blue water sources contributes significantly to stress-weighted water footprints. A main ingredient of Dolmio® pasta sauce is tomato. Due to the stress-heavy consumption of blue water in agriculture, tomatoes contributed more than 95% of stress-weighted water footprint. Therefore, efforts to reduce water footprint should focus on stress-heavy processes and not necessarily processes that use more water.

The study argues that the simplistic existing volumetric method is unequipped to accurately depict how production impacts water scarcity. This method is misleading and confusing as these water footprints do not accurately reflect a product’s impact on the water supply. A revised water footprint method would allow quantitative comparisons between products in terms of potential to contribute to water scarcity. Water footprint assessment methods need to accurately reflect the impact of consumption and this requires a revised approach that considers the incorporation of water stress characterization factors. The revised method will help corporations direct optimal actions to reduce negative impact of water supply and help consumers to make more informed purchases. 

Ecosystem model predicted water availability

Species distribution models typically use four common proxies for water in order to predict how water availability will impact future species distribution. However,  the affects of changes in vegetation structure and functioning on the water balance of terrestrial ecosystems are not accounted for. Hickler sought to assess whether the water availability measure commonly used in species distribution models properly account for hydrological effects of changes in vegetation structure and functioning (2009). In his study, ecosystem models LPJ- GUESS and LPF- DGVM which took into account soil water content along with variables based on climate. The projections for future water availability from four common proxies for water and the soil water content predicted by ecosystem models differ substantially. Winnie Wong
Hickler, T., Stepan F., Miguel B. A., Oliver S., Wilfried T., and Martin T. S., 2009. An ecosystem model-based estimate of changes in water availability differs from water proxies that are commonly used in species distribution models. Global Ecology and Biogeography 18, 304-313.

The paper focused on water availability in Europe. The LPJ-GUESS model includes a number of factors that influence water availability not account for in common proxies for water. LPJ- DGVM is a simplified ecosystem model that was also assessed. The four commonly used proxies for water availability used were total annual precipitation, total precipitation during water scarce periods (June, July and August), annual water deficit, sum of actual evapotranspiration divided by equilibrium evapotranspiration. Water stress experienced by plants are a function of water availability and both soil after and atmospheric variables are biologically meaningful. For tree species, the water content of soil is a more direct measure of water availability than variables purely based on climate.
The changes projected by the four proxies correlated with each other white these variable showed no or very weak correlations with the two ecosystem models. Projected changes in the four proxies for water availability indicate a net effect of increasing temperate  and annual rainfall in many areas will be drying over most of Europe. In contrast the ecosystem models the sign of change (positive or negative) differs in 32% of the total study area. These significant differences in results are important because results from species distribution models has been used for guiding policies for adaptation to climate change.