Regional cotton lint yield, ET c and water value in Arizona and California M.E. Grismer * Department of Biological and Agricultural Engineering, University of California, Davis, CA 95616, USA Accepted 22 August 2001 Abstract Watervalueasagricultureproductionmaybeoverlooked,thoughitisanimportantfactortorational water allocations within a region. An analysis of cotton Upland and Pima) lint yield, lint yield- consumptive use ratio LY:ET c ), water-use ef®ciency WUE) and lint price for Arizona AZ) and California CA) during 1988±1999 is considered as part of an attempt to determine lint water value, or bene®t. It included determination of means and variability of cotton lint production, LY:ET c ratios and associated irrigation water values IWVs) and compared these numbers with published estimates of WUE, forage hay water values and municipal water costs. Available rainfall, reference eva- potranspiration ET o ), lint yields and price data for counties in both states were used. Consumptive use was estimated using a four-stage crop coef®cient function veri®ed by literature values or County Advisor experience. As with dry matter production, cotton lint yields in interior valley regions of CA were weakly correlated with ET c and averaged 1.33 Mg/ha Upland) and 1.08 Mg/ha Pima). Cotton lint yields in desert regions of AZ and CAwere not correlated with ET c . The greatest LY:ET c ratios 1.9±2.1 kg/ha-mm) were in the San Joaquinvalley of CA, were similar to that from WUE type studies and resulted in gross IWVs 3400±3800 US$/ha-m), with relatively moderate variability at a net irrigation water requirement IWR) of approximately 720 mm. While this IWV is 2.5 times greater than water delivery prices below the California Delta, it is less than average municipal water costs of 4200 US$/ha-mforLosAngeles,SanFranciscoandPheonixwhiletheoverallAZ/CAaveragecotton lint IWVis considerably less. However, cotton lint IWVis two to three times greater than that obtained for alfalfa and sudangrass hay crops in all regions. # 2002 M.E. Grismer. Published by Elsevier Science B.V. All rights reserved. Keywords: Water-use ef®ciency; Crop yields; Evapotranspiration; Irrigation; Rainfall 1. Introduction As competition for water resources among municipal, industrial and agricultural sectors of the western USA states intensifies, an estimation of water value i.e. its cash Agricultural Water Management 54 2002) 227±242 * Tel.: 1-530-752-3243; fax: 1-530-752-5262. E-mail address: megrismer@ucdavis.edu M.E. Grismer). 0378-3774/02/$ ± see front matter # 2002 M.E. Grismer. Published by Elsevier Science B.V. All rights reserved. PII:S0378-377401)00174-3