Irrigation efficiency and water-policy implications for river basin resilience

摘要

Rising demand for food, fiber, and biofuels drivesexpanding irrigation withdrawals from surface water and groundwater. Irrigationefficiency and water savings have become watchwords in response toclimate-induced hydrological variability, increasing freshwater demand forother uses including ecosystem water needs, and low economic productivity ofirrigation compared to most other uses. We identify three classes ofunintended consequences, presented here as paradoxes. Ever-tighter cyclingof water has been shown to increase resource use, an example of theefficiency paradox. In the absence of effective policy toconstrain irrigated-area expansion using "saved water", efficiency canaggravate scarcity, deteriorate resource quality, and impair river basinresilience through loss of flexibility and redundancy. Water scarcity andsalinity effects in the lower reaches of basins (symptomatic of thescale paradox) may partly be offset over the short-term throughgroundwater pumping or increasing surface water storage capacity. However,declining ecological flows and increasing salinity have importantimplications for riparian and estuarine ecosystems and for non-irrigationhuman uses of water including urban supply and energy generation, examplesof the sectoral paradox. This paper briefly considers threeregional contexts with broadly similar climatic and water-resourceconditions – central Chile, southwestern US, and south-centralSpain – where irrigation efficiency directly influences basin resilience.The comparison leads to more generic insights on water policy in relation toirrigation efficiency and emerging or overdue needs for environmental protection.