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<br /> <br /> <br />.. <br /> <br />The quantity and seasonal distribl.\tion of the water supply will <br />usually affect consumptive use by crops and native vegetation. Where <br />water is plentiful, there is tendency to over~irrigate in frequency and <br />depth of application. If the soil surface is frequently wet and the re~ <br />sulting evaporation high, consumptive use will increase. Native plants <br />adapted to extreme economy of water in dry years produce more vigorous <br />gr,owth and have greater consumptive use rates in wet years. <br /> <br />. Consumptive use may be determined by soil moiSture studies, lysi~ <br />metet or tank measurements, analysis of irrigation and cli:ma.tological <br />data, .empirical formulas, inD.ow-outfl.ow measurements and other methods. <br />Measurements of consumptive use have been made in a few areas in the <br />Colorado River Basin, but additional data and research are necessary <br />before accurate determination can be made of evaporation andtr~nspira. <br />tion throughout the Basin. No data are available in many areas, so it has <br />been ;riecessary to compute consumptive use by formulas based 'on climatic <br />factors. Neglecting unmeasured factors, consumptive use varies with <br />temperature, daytime hours, and available moisture (precipitation, <br />irriga~ion and/or ground water). The procedure is to correlate exiSting <br />consumptive use data with these factors, and thus develop coefficient.s for <br />different crops that may then be applied in other areas wh.ere only cUmato- <br />logical data are available. By mUltiplying mean. mOnthly tempe.ra.ture (t) <br />by monthly percent of daytime hours of the year Ip), a monthly consumptive <br />use factor (f) is obtained. It is assumed that consumptive use varies <br />directly as this factor wh.en ample water is available. Mathematically, <br />U .. KF . sum of kf where - <br /> <br />" <br /> <br />. <br /> <br />. <br /> <br />U " Consumptive use of crop (or evaporation) in inches <br />for any period. <br />F " Sum of the monthly consumptive use factor s for the <br />period (sum of the products of mean monthly tem~ <br />perature and monthly percent of annual daytime <br />hours) (x pl. <br />K . Empirical cO.efficient (annual or irrigation season). <br />t .. Mean monthly temperature in degrees Fahre.nheit. <br />p .. Monthly percent of daytime hours of the year. <br />f " t x p Monthly consumptive use factor. <br />100 <br />k " Monthly coefficient. <br />u Ii kf Monthly consumptive use in inches. <br /> <br />. <br /> <br />Knowing the consumptive use requirement of water by a particular crop in <br />some locality, an estimate of the use by the same crop in s.ome other area <br />may be made by the form1:ll.a U .. KF. <br /> <br />The Division of Irrigation and the .Arizona Agricultural Experiment <br />Station conducted water use and irrigation studies in Salt River Valley <br />and other areas of Arizona. Use of water was determined by soil moisture <br />depletion method for various crops. Unit values of consumptive use were . <br />correlated with climatological data. and seasonal coefficients dete.rmined <br />for transfer of unit values to other areas. , Results are published in <br />"Consumptive Use and Irrigation Requirements of Crops in Arizona." The <br />Division of Irrigation made measurements of consumptive use, irrigatipn <br />requirements and evaporation in California in cooperation with State and <br /> <br />" <br /> <br />-13- <br />