The “Water Productivity” (WP) term describes the ratio between the quantity of an (agricultural) product (biomass, yield) and the amount of water depleted or diverted. Until 2050, human population is projected to increase to 9 billion people and it is estimated that 70 per cent of additional food will have to be produced in order to feed the humanity over the next 40 years. Meeting this challenge, the “Water Productivity term” plays a crucial role in modern agriculture which aims to increase yield production per hectare per unit of water used. Bearing in mind the consequences of climate change, an increase in water productivity helps to cope with predicted water scarcity in agriculture and serves as an indicator for sustainable agricultural intensification (FAO 2012). Expert survey participants in the World Water Scenarios Project of the United Nations World Water Assessment Programme (WWAP) ranked increases in water productivity in agriculture as the most important development affecting water (WWAP 2012).
More Crop per Drop
The concept of WP developed from separate fields, for example crop physiologists defined water – use efficiency as carbon assimilated and crop yield per unit of transpiration or as the amount of biomass per unit of Evapotranspiration. The current understanding of water productivity developed including the benefits and costs of water used for agriculture.
The concept of water productivity in agricultural production systems focuses on ‘”producing more food with the same water resources” or “producing the same'amount of food with less water resources”. Water productivity measures how a system converts water into goods and services, it is a measure of the beneficial output in relation to the water actually consumed, the ratio of the net benefits from crop, forestry, fishery, livestock and other mixed agricultural systems to the amount of water used in its production process. In a simple way, water productivity is defined as “crop production” per unit “amount of water used'”.
The basic equation to calculate WP is: WP = Output derived from water use/ Water Input The Water Input can be expressed by a set of choices according to the aim of the investigation. For example
- Irrigation diversion
- Gross/net inflow
The Water output or the benefits can also be measured with various terms, for example with
- Economic value (monetary)
- Physical mass (kilogram)
- Nutritional value (calories)
Therefore the calculated Indicator “Water Productivity” is expressed in different ways according to specific interests to examine water-use performances.
- WP expressed inkg/ might be of interest to an irrigation manager, while
- kg/m3 ET (Evapotranspiration) could be a key issue for plant breeders and agronomic scientists.
- WP in US$/m3 of ET is more interesting to a basin development agency that is concerned with overall water consumption and the outputs generated.
- A water resources planner might look at the difference between kg/m3 irrigation diversion and kg/m3 ET to assess how well irrigation water is managed.
The “water footprint”, the concept of water accounting by product, is also a way of expressing the WP of a given product or service, for example of the manufacturing industries (Cai et al. 2011, Singh 2005). Subsuming, the concept of water productivity describes various aspects of water management such as production, utilization and economy at different scales. These possible variations ensure the flexibility and robustness of the tool to measure efficiency of water use. Thus a conceptual framework for different stakeholders and researchers is provided.
Potential Measures to achieve higher WP
The objective of higher water use productivity can for example be pursued by
- increasing the marketable yield of the crops for each unit of water transpired
- reducing the outflows and the atmospheric water depletion
- enhancing the effective use of rainfall, of the water stored in the soil, and of the marginal quality water
To achieve these goals, a wide range of measures may be adopted, for example
In smallholder livestock systems, feeding animals crop residues can provide a severalfold increase in water productivity. Higher water productivity can also be achieved through virtual water trade. By growing crops in places where climate enables high water productivity at lower cost and trading them to places with lower water productivity, virtual water trade is already a reality for many water-scarce countries, and is expected to increase in the future (FAO 2012, Fader 2010).
Concerns about the scope and ease of achieving water productivity gains
Several publications show that there is considerable scope for improving crop water productivity through water harvesting, supplemental irrigation, deficit irrigation, precision irrigation techniques, and soil-water conservation practices.
But according to Molden (2010) and de Fraiture (2009), the scope and ease of achieving physical water productivity gains should not be assumed unfounded. They state that in most agricultural productive regions the WP is already quite high and perceived losses and inefficiencies might be lower than generally assumed. The re-use and recycling of water may be high too, and large gains through improvements in crop genetics are not foreseen in future. In other words, the enabling conditions for farmers and water managers are not in place to enhance water productivity. Some priority areas are defined where essential increases in WP are possible. These include areas where
- poverty is high and water productivity is low
- areas of physical water scarcity where competition for water is high
- areas with little water resources development
- areas of water-driven ecosystem degradation (falling groundwater tables, river desiccation) (Molden et al. 2010)
There is greater reason to be optimistic about increasing economic water productivity by switching to higher value agricultural uses and by reducing costs pf production.
GIZ Project Example - Agricultural Water Productivity as Adaptation to Climate Change (AWP-ACC)
Egypt’s climate can be categorized as hot arid desert climate with variable rainfall and recurrent droughts particularly in the northern Nile Delta. The natural resources, especially the limited water resources, are under great pressure. The Government of Egypt has responded to the pressing threat of climate change by forming an Climate Change Committee and developing various general and sector-specific strategies. The priority sectors water, agriculture, coastal zones, tourism, housing, roads, health were identified along with potential and priority mitigation and adaptation measures.
The Objective of the programme is to improve Agricultural Water Productivity as a means to adapt to climate change by optimizing fertilizer practices and pesticides, crop rotation and the planting calendar.
Adapted farming and improved irrigation-methods increase water productivity while protecting soil and water resources. Reuse of treated drainage and wastewater lead to a diversification of water resources, thus making farmers and other water users less vulnerable to unstable water supply. Ensuring and improving agricultural production provides food and income security.
Increased energy efficiency in water supply also increases water productivity while reducing the energy demand, thus contributing to both adaptation to and mitigation of climate change.
References and further information
- Cai, X. et al. (2011): Producing more food with less water in a changing world: assessment of water productivity in 10 major river basins. In: Water International, 36:1, 42-62
- Fader, M. (2010): Virtual water content of temperate cereals and maize: Present and potential future patterns. Journal of Hydrology 384, (3–4) 175-306
- FAO (2012): Coping with water scarcity. An action framework for agriculture and food security. Food and Agriculture Organization of the United Nations, Rome, 2012
- GIZ 2013: Agricultural Water Productivity as Adaptationto Climate Change (AWP-ACC)
- Halsema, van G.E. and Vincent, L. (2012): Efficiency and productivity terms for water management: A matter of contextual relativism versus general absolutism. In: Agricultural Water Management 108 9– 15
- Molden, D., et al., 2010. Improving agricultural water productivity: between optimism and caution. Agricultural Water Management, 97 (4), 528–535.
- Pereiraa, L. S., Corderyb, I., Iacovidesc, I. (2012): Improved indicators of water use performance and productivity for sustainable water conservation and saving. In: Agricultural Water Management 108, 39– 51
- Singh, R. 2005. Water productivity analysis from field to regional scale: integration of crop and soil modelling, remote sensing and geographical information. Doctoral thesis, Wageningen University, Wageningen, The Netherlands.
- WASAMED 2005: Water Use Efficiency and Water Productivity - Proceedings of 4th WASAMED (WAter SAving in MEDiterranean agriculture) Workshop. Amman (Jordan), 30 Sept. - 4 Oct. 2005. In: Options Méditerranéennes, Séries B n. 57
- WWAP (World Water Assessment Programme). 2012. The United Nations World Water Development Report 4: Managing Water under Uncertainty and Risk. Paris, UNESCO