Evapotranspiration: An Essential Observation for Climate Understanding and Efficient Water Management.
Department of the Interior Bureau of Reclamation A General Overview
Mission Statement The Bureau of Reclamation manages, develops, and protects water and related resources in an environmentally and economically sound manner in the interest of the American public.
Reclamation: • Is the nation’s largest wholesaler of water, operating 348 reservoirs with a combined total storage capacity of 245 million acre-feet. • Provides 140,000 western farmers with water, supplying 10 million acres. • Through 58 hydroelectric facilities generating an annual average of 40 billion Kilowatt-hours, is second largest hydropower producer in the United States. • Delivers 10 trillion gallons of water to greater than 31 million people each year. • Participates in managing 289 recreation sites with 90 million visitors each year.
Colorado River Compact • Agreement between 7 basin states negotiated in 1922. • Current allotment established in 1928. • Divides the Colorado River basin into an upper and lower division. • Upper Basin states demanded the allocation agreement before they would support any large dams on the river. • 1.5 million acre-feet allocated to Mexico in 1944.
ET Estimation/Calculation • Colorado River Basin Consumptive Uses & Losses (CU&L) • Lower Colorado River Accounting System (LCRAS)
Consumptive Uses & Losses Public Law 90-537 “…make reports as to the annual consumptive uses and losses of water from the Colorado River System after each successive 5-year period, beginning with the 5-year period starting October 1, 1970 … Such reports will be prepared in consultation with the States of the Lower Basin individually and with the Upper Colorado River Commission and will be transmitted to the President, the Congress, and the Governors of each State signatory to the Colorado River Compact."
Consumptive Uses & Losses • Agriculture (irrigated crops & livestock water use). • Reservoir evaporation. • Stockpond evaporation. • Thermal electric power. • Municipal. • Industrial (including mining operations). • Trans-basin diversions.
Consumptive Uses & Losses • Irrigated Agriculture • Monthly time-step. • Average monthly temperature and total precipitation from the western regional Climate Center. • Cropping data from crop maps (generated by the states and Reclamation), USDA Census of Agriculture, USDA National Agriculture Statistics Service. • Blaney-Criddle selected in the 1970’s. • Potential improvements • Better cropping data. • Meteorological data on a large-scale basis that could drive a more robust ET model (ie: Penman-Monteith). • Methods to help determine shortage areas.
Consumptive Uses & Losses • Stockpond Evaporation • Rainfall measurements required to calculate net evaporation. • Calculated a single pond with aggregate surface area equal to the sum of the individual ponds. • Potential improvements • Maps of actual stockpond locations and estimations of stockpond surface areas.
Lower Colorado River Accounting System Consolidated decree of the United States Supreme Court in Arizona v California, 547 U.S. 150 “The United States shall prepare and maintain … complete, detailed and accurate records of: Diversions of water from the mainstream, return flow of such water to the stream as is available for consumptive use in the United States or in satisfaction of the Mexican treaty obligation, and consumptive use of such water.”
Lower Colorado River Accounting System • Maintained by the Lower Colorado Region’s Water Conservation and Verification Group. • Provides estimates of irrigation and riparian ET as well as open water evaporation. • Et calculated using ASCE Penman-Monteith equation. • Acreage estimates from Thematic Mapper and ASTER sensors on Landsat 5 & 7, and Terra satellites. • Ground reference surveys used to verify and further define map products.
Lower Colorado River Accounting System • Potential improvements • Desire to be able to measure changes in ET of Tamarisk stands in the southwest as foliage is lost as a response to biological control efforts.
Metric & ReSet ET Tools • Reclamation has been recently investigating the Metric and ReSet energy balance models • Crop mapping is not required. • Potential for accurate mapping of ET in fields that do not receive full water allocations.
Additional Potential Needs • Climate change • Both long-term general trends and shorter-term cyclical variability. • High mountain meadows • Remote sensing of irrigation water application. • Multiple plantings in a given year • Current tools have difficulty in determining growth parameters (multiple alfalfa cuttings for instance). • Native vegetation versus irrigated crops • Stressed/shorted growth conditions versus abundant (relatively) water growth conditions.