Prediction Accuracy for Projectwide Evapotranspiration Using Crop Coefficients and Reference Evapotranspiration
Publication: Journal of Irrigation and Drainage Engineering
Volume 131, Issue 1
Abstract
The Imperial Irrigation District is a large irrigation project in the western United States having a unique hydrogeologic structure such that only small amounts of deep percolation leave the project directly as subsurface flows. This structure is conducive to relatively accurate application of a surface water balance to the district, enabling the determination of crop evapotranspiration as a residual of inflows and outflows. The ability to calculate from discharge measurements provides the opportunity to assess the accuracy and consistency of an independently applied crop coefficient—reference evapotranspiration procedure integrated over the project. The accuracy of the annual crop evapotranspiration via water balance estimates was at the 95% confidence level. Calculations using and were based on the FAO-56 dual crop coefficient approach and included separate calculation of evaporation from precipitation and irrigation events. Grass reference was computed using the CIMIS Penman equation and was computed for over 30 crop types. On average, -based ET computations exceeded determined by water balance (referred to as ) by 8% on an annual basis over a 7 year period. The 8% overprediction was concluded to stem primarily from use of that represents potential and ideal growing conditions, whereas crops in the study area were not always in full pristine condition due to various water and agronomic stresses. A 6% reduction to calculated -based ET was applied to all crops, and a further 2% reduction was applied to lower value crops to bring the project-wide ET predicted by -based ET into agreement with . The standard error of estimate (SEE) for annual for the entire project based on , following the reduction adjustment, was 3.4% of total annual , which is considered to be quite good. The SEE for the average monthly was 15% of average monthly . A sensitivity analysis of the computational procedure for showed that relaxation from using the FAO-56 dual method to the more simple mean (i.e., single) curve and relaxation of specificity of planting and harvest dates did not substantially increase the projectwide prediction error The use of the mean curves, where effects of evaporation from wet soil are included as general averages, predicted 5% lower than the dual method for monthly estimates and 8% lower on an annual basis, so that no adjustment was required to match annual ET derived from water balance. About one half of the reduction in estimates when applying the single (or mean) method rather than the dual method was caused by the lack of accounting for evaporation from special irrigations during the off season (i.e., in between crops).
Get full access to this article
View all available purchase options and get full access to this article.
Acknowledgments
The Imperial Irrigation District (IID) of southern California provided financial and technical support for this study in addition to vast amounts of cropping and water use data. The project is commended for its long-standing program of water measurement and data reporting.
References
Allen, R. G. (1996). “Assessing integrity of weather data for use in reference evapotranspiration estimation.” J. Irrig. Drain. Eng., 122(2), 97–106.
Allen, R. G., Pereira L. S., Raes, D., and Smith, M. (1998). “Crop evapotranspiration: Guidelines for computing crop water requirements.” United Nations Food and Agriculture Organization, Irrigation and Drainage Paper 56, Rome.
Allen, R. G., Pereira, L. S., Smith, M., Raes, D., and Wright, J. L. (2005). “The FAO-56 dual crop coefficient method for predicting evaporation from soil and application extensions.” J. Irrig. Drain. Eng., 131(1), 2–13.
American Society of Civil Engineers (ASCE). (2002). The ASCE standardized equation for calculating reference evapotranspiration, Environment and Water Resources Institute of ASCE, New York.
Burt, C. M., et al. (1997). “Irrigation performance measures: Efficiency and uniformity.” J. Irrig. Drain. Eng., 123(6), 423–442.
Clemmens, A. J., and Burt, C. M. (1997). “Accuracy of irrigation efficiency estimates.” J. Irrig. Drain. Eng., 123(6), 443–453.
Doorenbos, J., and Kassam, A. H. (1979). “Yield response to water.” United Nations Food and Agriculture Organization Irrigation and Drainage Paper No. 33, Rome.
Doorenbos, J., and Pruitt, W. O. (1977). “Crop water requirements.” United Nations FAO Irrigation and Drainage Paper No. 24, (revised), Rome.
Droogers, P., and Bastiaanssen, W. (2002). “Irrigation performance using hydrological and remote sensing modeling.” J. Irrig. Drain. Eng., 128(1), 11–18.
Gochis, D. J., and Cuenca, R. H. (2000). “Plant water use and crop curves for hybrid poplars.” J. Irrig. Drain. Eng., 126(4), 206–214.
Hawkins, R. H., Hjelmfelt, A. T., and Zevenbergen, A. W. (1985). “Runoff probability, storm depth, and curve numbers.” J. Irrig. Drain. Eng., 111(4), 330–340.
Imperial Irrigation District (IID). (2002). Imperial Irrigation District Conservation and Transfer Project Final Environmental Impact Rep. and Habitat Conservation Plan; State Clearing House No. 9091142, Sacramento, Calif.
Imperial Irrigation District (IID). (2003). “Description of the project.” ⟨http://www.iid.com/water/works-delivery.html, accessed March, 2004.⟩
Jensen, M. E., Burman, R. D., and Allen, R. G., eds. (1990). “Evapotranspiration and irrigation water requirements.” ASCE manuals and reports on engineering practice No. 70, New York, 360 pp.
Loeltz, O. J., Irelan, B., Robison, J. H., and Olmsted, F. H. (1975). “Geohydrologic reconnaissance of the Imperial Valley, California.” U.S. Geol. Surv. Prof. Pap., 486-K, 1–54.
Molden, D., and Sakthivadivel, R. (1999). “Water accounting to assess use and productivity of water.” Water Res. Dev., 15, 55–71.
Pruitt, W. O., Swan, B. D., Held, A., Sutton, B., Matista, A., and Hsiao, T. C. (1987). “Bowen ratio and Penman: Australian-California tests.” Irrig. Systems for the 21st Century, Proc. Irrig. and Drain. Specialist Conf; ASCE, Portland, Ore., 149–158.
Setmire, J. G., Schroder, R. A., Densmore, J. N., Goodbred, S. L., Audet, D. J., and Radke, W. R. (1993). “Detailed study of water quality, bottom sediment and biota associated with irrigation drainage in the Salton Sea area, California, 1988–1990.” U.S. Geological Survey Water Resources Investigation Rep. No. 93-4014, Washington, D.C.
Snyder, R. L., Lanini, B. J., Shaw, D. A., and Pruitt, W. O. (1989a). “Using reference evapotranspiration (ETo) and crop coefficients to estimate crop evapotranspiration (ETc) for agronomic crops, grasses, and vegetable crops.” Leaflet No. 21427, Cooperative Extension, Univ. of California, Berkeley, Calif.
Snyder, R. L., Lanini, B. J., Shaw, D. A., and Pruitt, W. O. (1989b). “Using reference evapotranspiration (ETo) and crop coefficients to estimate crop evapotranspiration (ETc) for trees and vines.” Leaflet No. 21428, Cooperative Extension, Univ. of California, Berkeley, Calif.
Soil Conservation Service (SCS). (1972). National engineering handbook, Sec. 4, Chaps. 7–10, Washington, D.C.
Szilagyi, J., Katul, G. G., and Parlange, M. B. (2001). “Evapotranspiration Intensifies over the Conterminous United States.” J. Water Resour. Plan. Manage., 127(6), 354–362.
Wahlin, B. T., Replogle, J. A., and Clemmens, A. J. (1997). “Measurement accuracy for major surface-water flows entering and leaving the Imperial Valley.” WCL Rep. No. 23, Prepared for U.S. Water Conservation Laboratory, Phoenix, Water Resources Publications, LLC., ⟨http://www.wrpllc.com⟩
Water Study Team (WST). (1998). Imperial Irrigation District water use assessment for the years 1987–1996, Imperial Irrigation District, Imperial, Calif.
Zimmerman, R. P. (1981). Soil survey of Imperial County, California, Imperial Valley area, U.S. Dept. of Agriculture, Soil Conservation Service, Washington, D.C.
Information & Authors
Information
Published In
Copyright
© 2005 ASCE.
History
Received: Feb 27, 2003
Accepted: Jan 8, 2004
Published online: Feb 1, 2005
Published in print: Feb 2005
Authors
Metrics & Citations
Metrics
Citations
Download citation
If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download.