By Sonia A. Hall
There is a difference between the amount of water diverted from streams and rivers to irrigate crops, and the amount of water consumptively used in those irrigated fields, which includes what the crops actually transpire, plus what evaporates from these fields. The difference is sometimes called return flow, as it percolates through the soil and becomes available for use further downstream (this earlier article has a diagram that reflects that, so take a look).
Decisions about water allocation and water use in the Pacific Northwest are mostly made based on diversions, because that’s what we can measure, using water meters for example. But when we discuss whether more efficient irrigation technology should be used, or ways to reduce conflicts between out-of-stream and instream water needs, consumptive use—the water used by crops and lost to evaporation—is also really important. Check out this article on METRIC, a method using remote sensing to measure water consumption in Idaho. And take a look at the 2016 Columbia River Forecast for a pilot application of METRIC in Washington State, work that is currently being expanded with support from the US Department of Agriculture as part of the Washington State University led Technology for Trade project. What do you think would be the benefits of having this technology available across the Columbia River Basin? Take a minute to comment below. And stay tuned for more on METRIC as this research progresses.