Monday, April 19, 2010
When Irrigation Efficiency Saves Water
Another example that comes to mind is in a groundwater situation where there is a shallow, unusable aquifer perched above the irrigation water source, AND, all deep aquifer recharge is from lateral sources not connected to the perched aquifer. In other words, the inefficient water use collects in the shallow, unused, perched aquifer and never returns to the original source. Again, irrigation efficiency improvements under these conditions will clearly save water within the deep source aquifer. But again, no one can be using (have rights to) the shallow water supply because the efficiency improvements, if taken far enough, are eventually going to eliminate its source.
In both of the cases just discussed, it should be noted that the consumptive crop water use does not change after the improvements - the crops continue to consume the same amount of water as before. The savings come from the elimination of the inefficient water application that was not returning to the original source. This is all water that, after the improvements, no longer needs to be pumped. These situations extend the life of the original water source - which even I can define as conservation.
Other than these specific conditions, irrigation efficiency improvements do not conserve water much at all - certainly not enough to spend the amount of money folks are suggesting. There are other benefits to increased irrigation efficiencies - like reduced energy and reduced crop inputs and a better farm operation bottom line. Let's do it for these reasons, but be aware that consumptive water use is not being affected and it's the consumptive water use that changes aquifer storage volumes. The fact that most argue these improvements also increase production per unit of pumped water probably tells us right off the bat that consumptive water use is increasing as a result - regardless of what pumped water is doing.
Before you buy into irrigation efficiency improvements, make sure you understand what problem it is you're trying to impact, what benefits these efforts will have, and at what cost.