Irrigation Efficiency vs. Water Productivity: Uses, limitations and misinterpretations
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1) The document discusses the concepts of irrigation efficiency and water productivity, noting important distinctions in their definitions, scales of analysis, and limitations. 2) It provides an example from Zhanghe Irrigation District in China where improvements to both on-farm water management and water allocation policies led to increased water productivity while maintaining agricultural output. 3) Key lessons are that strategies to improve water management need to consider perspectives of different water user groups and potential impacts at broader basin scales, and that multiple indicators of water productivity are needed to fully understand complex agricultural systems and trade-offs.
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Irrigation Efficiency vs. Water Productivity: Uses, limitations and misinterpretations
- 1. Irrigation Efficiency vs. Water Productivity: Uses, limitations and misinterpretations World Bank – Water Week 5 April 2016 Jeremy Bird and Meredith Giordano International Water Management Institute
- 2. What scale?: Farm, project, basin, national, … Whose perspective?: • Farmer’s costs; • Scheme manager’s performance; • Planning processes - water balance; • SDG monitoring • Other? What objectives are we trying to address? Shah 2009
- 3. • Appropriate for: o Farm-scale irrigation investment and management decisions o Assessing “losses” in irrigation application, distribution and conveyance systems; designing systems o “real-time” M&E of irrigation system operational performance • Limitations: o Does not account for the capture and re-use of water within broader hydrologic systems (e.g., basins) o Can lead to incorrect water allocation and investment decisions, ‘faulty’ public policy at the basin scale Irrigation efficiency: uses and limitations Defined as: water consumed relative to water applied or withdrawn from a source – input/output measure
- 4. Egypt’s Nile Valley: Classical View: ~ 40% efficient, suggesting considerable opportunity to reduce water losses Taking into account water reuse, ~84% of water available is depleted (or consumed) by crops, municipal, industrial and navigational purposes. Irrigation efficiency: example of limitations Molden et al. 1998a
- 5. • Appropriate for: o Informing water allocation negotiations between users (basin and farm scale) o Assessing measures to intensify water use o Post-season performance assessment of irrigated agriculture • Limitations: o Less applicable for operational management decisions o More complex to evaluate Molden 1997 Water productivity as an alternative measure Defined as : Output (kg/$/kcal) in relation to water use (in terms of water withdrawn, applied or consumed)
- 6. Application: at different scales, for different purposes and users Water productivity – being clear on objectives Cook et al. 2006
- 7. Water productivity interventions must consider farmer adaptation strategies, their impacts at basin scales, and institutional arrangements to address possible trade- offs. At global scale, maybe also considerations of virtual water? To promote “wet” water savings, surface water users in the Arkansas River Basin have been required to return water savings arising from more efficient irrigation technology adoption to the river. Harvey 2014 Upstream Wyoming implements water saving technologies; downstream Montana no longer gets its share (Supreme Court Op 137). Stermitzetal.USGS Water productivity: why scale matters
- 8. Molden 1997 Water productivity – the importance of taking a broader perspective Water Accounting: How much water is actually depleted, where and for what use, compared to that available and the portion diverted?
- 9. Economic water productivity by crop, Indus-Ganges basin. Useful for crop comparison, but doesn’t include other economic uses which may be important for setting policy Cai et al. 2011 Water productivity – comparison by crop over time and space
- 10. Photo:DavidBrazier/IWMIPhoto:TomvanCakenberghe/IWMIPhoto:DavidBrazier/IWMIPhoto:DavidBrazier/IWMI Water supplied by the Zhanghe Reservoir and Rice Production in the Zhanghe Irrigation District (1965-2005) Reallocation accomplished with only a modest decline in total rice production and increased agricultural water productivity Zhange He case study: policy of reallocation Loeve et al. 2007
- 11. • Rehabilitation and construction of new farm ponds • Water conservation practices (alternate wetting and drying and use of recycled water) • Introduction of volumetric pricing • Introduction of new rice varieties and the use of chemical fertilizers (improving rice yields) Zhang He: factors affecting the change
- 12. Photo:DavidBrazier/IWMIPhoto:TomvanCakenberghe/IWMIPhoto:DavidBrazier/IWMIPhoto:DavidBrazier/IWMI Zhang He: disaggregated contributions from agriculture improvement and water management Note: Water Productivity here is measured using crop output per cubic meter of water withdrawn – the classic ‘crop per drop’ case. If a basin perspective is required, then measuring crop output per unit of water consumed is more appropriate. Loeve et al. 2007
- 13. Zhang He: incentives and pressures to save or reallocate water by ‘user’ and ‘scale’ Adapted from Molden et al. 2007
- 14. • Reallocation from the reservoir made possible due to a range of technical, managerial and policy interventions that supported both water conservation at the farm level, access to new water sources (ponds) and new rice varieties • Aligning the policies and strategies for changing water use and management across user groups/scales supported the objective of reallocating water • Need to be clear about the definition and interpretation of water productivity gains. o In this case water productivity measured in terms of irrigation water supplied from the reservoir (not water consumed/depleted): relevant for field and project level comparison over time, but not basin-wide Lessons from Zhang He study
- 15. Increase the productivity per unit of water consumed/withdrawn (e.g., change crop varieties or type, improve timing/application of water, non-water inputs) Reduce non-beneficial depletion (e.g., non-beneficial evaporation, flows to sinks) Reallocate water among users (e.g., from lower to higher value uses) Tap uncommitted flows (e.g., storage, water reuse) Being clear on you objectives related to water productivity
- 16. Emerging discussion on SDG 6 indicators 6.4.1: Percentage change in water use efficiency over time • Intent is to measure relationship between economic output of water for different uses in relation to volume of water withdrawn 6.4.2: Level of water stress: freshwater withdrawal as proportion of freshwater available • An estimate of pressure from economic activities on the resource
- 17. Bastiaanssen et al. 2014 Overcoming data limitations – Water Accounting + Developments in water accounting, remote sensing, modeling aim to lessen the impact of data limitations.
- 18. • A focus on agricultural water productivity has brought greater attention to critical water scarcity issues and possible strategies to address them. • Tools such as water accounting are fundamental to understand how water is used and re-used within and across sectors at different scales. • However, reliance on single factor metrics in multi-factor and multi-output production processes can mask the complexity of agricultural systems and the trade-offs required to achieve desired outcomes • Important to consider water productivity as one of many indicators to be monitored (rather than a variable to be maximized) Consequences for investment in water management
- 19. ‘More crop per drop’ is only one aspect – and often not the most important. Using a set of complementary water productivity indicators (physical/economic; field level/basin level) can be matched to the intended objective: • Returns to farmer • Project level performance • Basin planning and trade off decisions • Achievement of SDGs • Etc. Segway to next presentation – broader economic considerations…
- 20. ‘A key lesson is that policies and strategies for changing water use and management need to consider the often different perspectives, objectives and incentives across user groups and the potential impacts at broader (basin) scales’. Some reflections Meredith Giordano – perscomm Author of the forthcoming World Bank report BEYOND “MORE CROP PER DROP”: EVOLVING THINKING ON AGRICULTURAL WATER PRODUCTIVITY
- 21. Visit our websites iwmi.org wle.cgiar.org wateraccounting.org and the Thrive blog at wle.cgiar.org/blogs
Hinweis der Redaktion
- Shah 2009
- “The classical concepts of irrigation efficiency have been appropriate for farmers making irrigation management decisions and for planners designing irrigation conveyance and application systems. But applying classical efficiency concepts to water basins as a whole leads to incorrect decisions and, therefore, to faulty public policy.” (Keller and Keller 1995) A common perception is that increasing efficiency in agriculture is the solution to the perceived water crisis. Technically defined, efficiency estimates how much diverted water reaches the crop, and how much is wasted "down the drain". However real "wastage" is due the result of not being as productive as possible with the water that is consumed in agriculture. For the Chistian Irrigated area, in Punjab Pakistan, IWMI calculated the water accounts for the 1993/94 agricultural year showing 740 million cubic meters (MCM) of water entered the area from irrigation deliveries, rain and groundwater. Agriculture consumed 90% of the supplies, evidently quite efficient and showing, from a larger basin perspective, farmers are very effective in converting water into crop production. However, with excessive groundwater abstraction very little water was available for flushing salts or for ecosystem sustenance. Farmers in the Christian area are, if anything, too efficient! Certainly increasing the efficiency, and leaving even less for other uses, is not recommended. While efficiency is very high, productivity is very low with Wheat yields of the order of 2.0 t ha-1 and rice yields of about 1.4 t ha-1. Water productivity of wheat at 0.6 kg m-3 was towards the low end of the spectrum when compared to global range 0.5 go 1.5 kg m-3. Increasing water productivity in these conditions will require improved field agronomy and crop management. Why is getting more crop per drop so important? The answer is simple -- growing more food with less water alleviates scarcity, contributes to achieving food security, and puts less strain on nature.
- This example illustrates a case where a large proportion of depleted water (84%) is used for intended (“process”) purposes (crop production, municipal, industrial and navigational uses). Converting the non-beneficial portion of the remaining, non-process depletion (e.g., non beneficial drainage or drainage in excess of environmental requirements) could allow for some improvements in the productivity of water (Molden et al. 1998a). Sources: Keller, A.; Keller, J.; Seckler, D. 1996. Integrated water resource systems: Theory and policy implications. Colombo, Sri Lanka: International Irrigation Management Institute (IIMI). 18p. (IIMI Research Report 3). Keller, A. A.; Keller, J. 1995. Effective efficiency: A water use efficiency concept for allocating freshwater resources. Arlington, VA, USA: Winrock International. Center for Economic Policy Studies. 19p. (Winrock International Discussion Paper Series 22) Molden, D.J.; El Kady, M.; Zhu, Z. 1998. Use and productivity of Egypt's Nile water. In: Contemporary challenges for irrigation and drainage: Proceedings from the USCID 14th Technical Conference on Irrigation, Drainage and Flood Control, Phoenix, Arizona, June 3-6, 1998, eds., Burns, J.I.; Anderson, S.S. Denver, CO, USA: USCID. Pp. 99-116.
- Water productivity can be applied at different scales—such as crop, field, farm, irrigation system or the basin-level—depending on the purpose and user of the analysis (Table 1). Source: Adapted from Molden 1997; Molden et al. 2003; Cook et al. 2006b; Molden et al. 2007b. Molden, D. 1997. Accounting for water use and productivity. Colombo, Sri Lanka: International Irrigation Management Institute (IIMI). 25p. (SWIM Paper 1). Molden, D.; Oweis, T.Y.; Pasquale, S.; Kijne, J.W.; Hanjra, M.A.; Bindraban, P.S.; Bouman, B.A.M.; Cook, S.; Erenstein, O.; Farahani, H.; Hachum, A.; Hoogeveen, J.; Mahoo, H.; Nangia, V.; Peden, D.; Sikka, A.; Silva, P.; Turral, H.; Upadhyaya, A.; Zwart, S. 2007b. Pathways for increasing agricultural water productivity. In: Water for food, water for life: A comprehensive assessment of water management in agriculture, ed., Molden, D. London, UK: Earthscan; Colombo, Sri Lanka: International Water Management Institute (IWMI). Pp. 279-310. Molden, D. Murray-Rust, H., Sakthivadivel R., and Makin I. 2003. A Water productivity Framework for understanding and action. In: Water productivity in agriculture: Limits and opportunities for improvement, eds., Kijne, J.W.; Barker, R.; Molden. D. Wallingford, UK: CABI; Colombo, Sri Lanka: International Water Management Institute (IWMI). Pp. 273-287. (Comprehensive Assessment of Water Management in Agriculture Series 1). Cook, S.; Gichuki, F.; Turral, H. 2006b. Agricultural water productivity: Issues, concepts and approaches. Colombo, Sri Lanka: International Water Management Institute (IWMI). Challenge Program Secretariat. 17p. (Challenge Program on Water and Food, Basin Focal Project Working Paper 1).
- Harvey N, 2014. The efficiency dilemma. Colorado Foundation for Water Education. https://www.yourwatercolorado.org/cfwe-education/headwaters-magazine/archive/305-headwaters-magazine/headwaters-fall-2014-eastern-plains/702-efficiency
- The water accounting framework was developed as a means to demonstrate how much water is actually depleted in a given domain, where and for what use, compared to what is available. Water accounting uses a ‘water balance’ approach to quantify the amount of water entering a system (through precipitation and river and groundwater flows) and the amount leaving a system (through evaporation, plant transpiration and river and groundwater flows). The amounts depleted within the basin are then classified according to use, whether or not the use is intended and whether or not it is beneficial. The amount of unused water flowing out of the system is classified according to whether or not it is committed for downstream use. Non-committed outflows are further subdivided into water that is currently utilizable and water that is not utilizable without additional infrastructure (Molden and Sakthivadivel. 1999). This approach has evolved into Water Accounting Plus (WA+), Box 6. The International Commission on Irrigation and Drainage (ICID) proposed that water use is the application of water to any particular purpose – fisheries, hydropower, irrigation, factories, etc Perry C J. 2012. Future of Irrigation and Drainage Design and Development, Asian Irrigation Forum. In addition: http://www.agwaterconservation.colostate.edu/FAQs_AGWATERCONSERVATIONPRACTICES.aspx provides a good compilation of answers to frequently asked questions about water conservation practices. The source of water includes withdrawals (surface diversion and/or groundwater abstraction) and/or rainfall.
- Zhanghe system. In this case, a number of interventions (agronomic, managerial and policy interventions) were introduced to accommodate a reallocation of irrigation water from the main reservoir to other sectors (hydropower, industry, domestic use). Factors affecting the reallocation included: a) improvement in existing ponds/building new farm ponds; b) adoption of water conservation practices, such as alternate wetting and drying, and recycling of water; c) volumetric water pricing; and d) the introduction of new rice varieties/use of chemical fertilizers. Water productivity improved per unit of water supplied from the reservoir (even when adjusting for the influence of improved rice yields). However, farmers were able to compensate for some of the reduced supply by accessing other sources of water (e.g., local storage through on farm ponds) so the basin-level impacts are not completely clear. Over a period of ~ 30 years a steady decline in water releases for agriculture from the Zhanghe Reservoir Water from the reservoir was reallocated to other sectors including hydropower, industry and domestic use.
- NOTES: Water productivity = yield per unit of water released from the Zhanghe reservoir Water productivity figures are adjusted in the final column to eliminate influence of yield increases
- Figure shows the trend in water productivity per unit of irrigation water (from Zhanghe reservoir, small reservoirs and other sources) due to both yields and other factors. Here water productivity is measured related to water withdrawn not water consumed. The large year to year variation in water productivity per unit of irrigation water can be attributed to variation in climatological factors; mainly the amount and distribution of rainfall during the rice growing season. A second (counterfactual) trend line shows the growth in irrigation water productivity assuming that yields had been constant at 1966–1974 levels. This reveals that irrigation water productivity rose due to increased yield improved water management practices until the 1990s (Loeve et al. 2004). Increase in rice yields has been the most important single factor contributing to the reasonably stable level of rice production over the period despite the sharp drop in rice acreage (Table 2). Volumetric pricing at the village level was introduced in the late 1980s (Mao and Li 1999; Li 2006). Several authors (Mao and Li 1999; Li et al. 2003; Li and Barker 2004) state that the introduction of volumetric pricing in ZIS provided an incentive on the part of farmers to save water. However, others like Yang et al. (2003) in a study in Northern China state clearly that volumetric pricing of irrigation alone is not a valid means of encouraging water conservation under current irrigation management institutions and Liao et al. (2007) in a study in three irrigation systems in China come to the same conclusions. In Zhanghe it was found that even though farmers pay a water fee per area they are quite aware of the link between the volume of water used and the price they pay for water (Loeve et al. 2001).