The UC Davis Center for Watershed Sciences has recently been extensively studying water consumption through evapotranspiration (ET) for the Delta Protection Commission (DPC). Transpiration is a scientific process exhibited by plants where moisture is carried through the roots, to the leaves, and then evaporates into the atmosphere. According to the U.S. Geological Survey, studies show about ten percent of the moisture found in the atmosphere on Earth is released by plants through transpiration, while most of the remaining 90 percent comes from evaporation of oceans, lakes, rivers, and other bodies of water.
ET is a combination of that transpiration from crops, trees, flowers, grass, etc., and the loss of water through evaporation from the earth's ground and waterbodies into the atmosphere. Understanding ET in the Delta is important to determine the overall amount of water consumed by various types of plants and environments.
Senate Bill 88 calls for measurement and reporting requirements of farmers who divert ten acre-feet of water or more annually. Now that farmers have mandatory reporting requirements regarding their consumptive water use, more studies are being conducted to find better monitoring alternatives to reduce the cost and time associated with meeting the requirements.
The UC Davis Center for Watershed Sciences recently studied consumptive water use in crop farming, with a focus on remote sensing using satellites. The study examined eight different crops from a group of islands in the Delta: Lower, Middle, and Upper Roberts Island, Ryer Island, and Back Tract Island. Their findings show that the remote-sensing method used is more accurate, consistent, and less costly.
At a DPC meeting in West Sacramento on November 16, Delta Watermaster Michael George commented about understanding ET in water hyacinth, an aquatic invasive species of plant currently being combated in Delta waters. George said, “One of the things we believe is that understanding the ET of hyacinth should actually draw more money for managing it...One of the things that I would hope will come out of this is a better understanding of the water cost, and therefore, the value of managing water hyacinth.”
UC Davis also conducted the Delta Consumptive Water Use Comparative Study sponsored by the State Water Resources Control Board and the Delta Stewardship Council, which included seven independent research teams that used seven different methods to estimate ET in crops. Part of the study involved collecting data on consumptive use of crops in fallow land below sea level.
Continuing to build the best available science not only serves the academic community, it also enables farmers in the Delta to make calculated decisions and cut costs. The new information on consumptive use is a welcome addition for the responsible management of our shared water supply.