Aqueous Productivity: An enhanced productivity indicator for water

- Water productivity (WP) is a widely-accepted performance indicator for water.
- The use of WP, while intuitive and appealing, is problematic in certain contexts.
- This research forwards 'aqueous productivity' (AP) as an alternative indicator.
- AP addresses some WP limitations and enhances productivity estimates for water.
- However, AP implementation should keep the method's limitations in consideration.

SummaryIncreasing demand for scarce water supplies is fueling competition between agricultural production and other municipal and environmental demands, and has heightened the need for effective indicators to measure water performance and support water allocation and planning processes. Water productivity (WP), defined as the 'ratio of the net benefits from crop, forestry, fishery, livestock, and mixed agricultural systems to the amount of water required to produce those benefits', is one such indicator that has gained prominence, particularly in research-for-development efforts in the developing world. However, though WP is a framework well-suited to systems where water use is directly attributable, particularly via depletion, to definitive benefits, the suitability of the approach becomes questionable when these conditions are not met, such as in multiple use systems with high re-use and non-depleting uses. These factors furthermore make WP highly scale-dependent, complicating comparative studies across scales and systems. This research forwards 'aqueous productivity' (AP) as an alternative indicator that addresses some inherent limitations in the WP approach and enhances productivity estimates for water in integrated systems. Like WP, AP is expressed as a ratio of benefit to water volume. However, AP uses a systems approach and is based on the concept that elements within a hydrologic system are linked via water flow interactions, and that those elements either 'extract' value from associated water flows or 'infuse' value into them. The AP method therefore calculates the 'aqueous productivity', a ratio indicating the 'dissolved' production-related economic value of all downstream uses of an individual water flow, for each inter-element and cross-boundary flow in the system. The AP conceptual framework and analytical methodology are presented. The method is then applied to two example hydroeconomic systems and compared to equivalent WP analysis. Discussion compares and contrasts the two methods, with a particular focus on how the AP approach addresses limitations in the WP method through its treatment of multiple uses of water and water re-use, seamless integration of depleting and non-depleting water uses, explicit cross-scale linkages, and incorporation of water storage and other temporal aspects in the analysis. Appropriate contexts of application for AP in decision support and in contrast to other water valuation methods are consequently considered.