A new report warns that conversion from flood or sprinkler irrigation to agricultural drip irrigation keeps water from replenishing aquifers, and can reduce locally available water.
It's always a bit disheartening when an environmental sacred cow is discovered to be made of fool's gold. But that's what the authors of a new report on agricultural irrigation are saying. The report is fairly dense to read, but the bottom line of the analysis is as follows:
"Our findings also suggest that where return flows are an important source of downstream water supply, reduced deliveries from the adoption of more efficient irrigation measures will
redistribute the basin’s water supply, which could impair existing water right holders who depend on that return flow. Our results indicate that water conservation subsidies will not provide
farmers with economic incentives to reduce water depletions and therefore are unlikely to make new water available for alterna- tive uses. In fact, depletions are likely to increase as a result of subsidies."
The report acknowledges real solutions to water needs are "elusive," but the authors argue that technological tools that increase irrigation efficiency will not necessarily reduce scarcity.
What approaches would be more effective at achieving balance between water needs and uses?
Measure More Accurately. A first step could be accurate accounting of basinwide water use. Water accounting analyzes use, depletion, and productivity of water at the basin
Switch Crops. Other measures include reducing or converting nonbeneficial evaporation from soil or supply sources to beneficial crop ET, restricting acreage or water use expansion in cropped areas, switching to lower water-consuming crops, or irrigating current crops at a deficit.
Close Water Rights Loopholes. Careful definition and administration of water rights can play a role. Water rights, water markets, water transfers, and water accounting need to be defined in terms of water depleted, not just water applied. Without defining water use in terms of depletions, individual farmers who invest in more efficient irrigation systems recognize that they apply less water per acre. They may believe their water right is no longer fully used and may claim that the unused water is available for beneficial use—Indeed, where hydrologic realities of a river basin are implemented into law, the right to acreage farmed and to water applied will be reduced after measures are taken to increase irrigation efficiency
That last recommendation, ending the misconception by farmers that any water they save is still theirs to use, is the one the researchers emphasized most strongly. But they know also, it's not one likely to be accepted easily by farmers. It will take some serious policy struggle to make it happen.