Water productivity in agriculture: limits and opportunities for improvement

Abstract

Substantially increasing the productivity of water used in agriculture is essential to meet goals of food and environmental security. Achieving these increases requires research that spans scales of analysis and disciplines. In spite of its importance, we do not have a common conceptual framework and language to facilitate research and communication among stakeholders. The objective of this chapter is to propose a common conceptual framework for water productivity. In a broad sense, productivity of water is related to the value or benefit derived from the use of water. Definitions of water productivity differ based on the background of the researcher or stakeholder. For example, obtaining more kilograms per unit of transpiration is an important means of expressing productivity of water when the interest of analysis is crops. At the basin scale, obtaining more value from water used from irrigated and rain-fed crops, forests, fisheries, ecosystems and other uses is of importance. There are several interrelated definitions of water productivity that are important across scales and domains of analyses. We propose in this chapter a set of definitions for water productivity and show how these are related across scales.As the analysis moves from individual plants to fields, farms, irrigation systems and water basins, different processes and means of analysis are important. Understanding how measures of water productivity scale up and scale down provides the key to how a group of people of diverse disciplines can work together on this topic. For example, crop scientists and breeders may focus on obtaining more mass per unit of transpiration, while planners and economists may consider policies to allocate water and land resources between different uses. To capture the full benefits of improved water productivity at farm level, it is necessary to integrate these with system-and basin-level changes. We provide a framework to show the interrelationship of the work of various disciplines. 4 D. Molden et al. Box 1.1. Water-accounting definitions.Gross inflow is the total amount of water flowing into the water-balance domain from precipitation and from surface and subsurface sources.Net inflow is the gross inflow plus any changes in storage.Water depletion is a use or removal of water from a water basin that renders it unavailable for further use. Water depletion is a key concept for water accounting, as interest is focused mostly on the productivity and the derived benefits per unit of water depleted. It is extremely important to distinguish water depletion from water diverted to a service or use, as not all water diverted to a use is depleted. Water is depleted by four generic processes:Evaporation: water is vaporized from surfaces or transpired by plants.Flows to sinks: water flows into a sea, saline groundwater or other location where it is not readily or economically recovered for reuse.Pollution: water quality gets degraded to an extent where it is unfit for certain uses.Incorporation into a product: through an industrial...

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