Irrigation Efficiency vs. Water Productivity: Uses, limitations and misinterpretations

World Bank – Water Week5 April 2016

Jeremy Bird and Meredith Giordano International Water Management Institute

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

• Appropriate for: o Farm-scale irrigation investment and management decisionso Assessing “losses” in irrigation application, distribution and

conveyance systems; designing systemso “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Defined as: water consumed relative to water applied or withdrawn from a source – input/output measure

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

• Appropriate for: o Informing water allocation negotiations between users

(basin and farm scale)o Assessing measures to intensify water useo Post-season performance assessment of irrigated

agriculture

• Limitations:o Less applicable for operational management

decisionso 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Defined as : Output (kg/$/kcal) in relation to water use (in terms of water withdrawn, applied or consumed)

Application: at different scales, for different purposes and users

Water productivity – being clear on objectives

Cook et al. 2006

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).

Ster

mitz

et a

l. U

SGS

Water productivity: why scale matters

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?

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

Phot

o: D

avid

Bra

zier/

IWM

IPh

oto

:Tom

van

Cak

enbe

rghe

/IW

MI

Phot

o : D

avid

Bra

zier/

IWM

IPh

oto:

Dav

id B

razie

r/IW

MI

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

• 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

Phot

o: D

avid

Bra

zier/

IWM

IPh

oto

:Tom

van

Cak

enbe

rghe

/IW

MI

Phot

o : D

avid

Bra

zier/

IWM

IPh

oto:

Dav

id B

razie

r/IW

MI

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

Zhang He: incentives and pressures to save or reallocate water by ‘user’ and ‘scale’

Adapted from Molden et al. 2007

• 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

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

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

Bastiaanssen et al. 2014

Overcoming data limitations – Water Accounting +

Developments in water accounting, remote sensing, modeling aim to lessen the impact of data limitations.

• 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

‘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…

‘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 – perscommAuthor of the forthcoming World Bank reportBEYOND “MORE CROP PER DROP”: EVOLVING THINKING ON AGRICULTURAL WATER PRODUCTIVITY

Visit our websites

iwmi.orgwle.cgiar.org wateraccounting.org

and the Thrive blog atwle.cgiar.org/blogs

Photo: Jim Holmes / IWMI