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<br />84
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<br />CONGRESO GEOLOGICO INTERNA(;IONAL
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<br />movement, rainfall, length of growing season, and day time hours. Of these,
<br />temperature exerts the grelitest effect. It controls the length of the period dur,
<br />ing which water is consumed -the growing season and also the rate of use
<br />during that period, Studies of the< use water by saltecedar on the Gila River
<br />in the so.uthwestern United States revealed 'that transpiration began in the
<br />spring when the monthly meron of the daily maximum air temperature rose
<br />above 730F, and ceased in the fall when it fell below 730F (Gatewood, Robin,
<br />son, Colby, Hem, and others, 1950, p. 11'5). It was found also that during
<br />the growing season the use of water closely paralleled the seasonal changes
<br />in temperature, increasing as the air temperatures increased and decreasing
<br />as they decreased,
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<br />Evapotranspiration at water table
<br />depths of 3ft., 2ft.} 1ft.
<br />Carlsbad 70/l~
<br />Owens Valley 68<1
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<br />Los Griegos G2b
<br />Santa A.na 610~
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<br />San Luis Valley 54.0
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<br />Evapotranspiration, het
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<br />Fig. 3-Relation ~f evapotranspir.ation by saltgfBSS, grown in tanks, to depth to water
<br />table and to the average temperature during the growing season.
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<br />The extent to which temperature affects the seasonal use of water by salt.
<br />are based on experimental data obtained at the "five locations in the western
<br />United States shown in figure 3 A, where the average temperature during the
<br />growing season ranged from 540 to 70oF. They show for depths of 1, 2, and
<br />3 feet a rapid increase in use with temperature. The curves indicate- that, for
<br />a 160F increase in air temperature during the growing season, the water
<br />requirement increaS€5 about 100 percent. In other words, the water require-
<br />ment of saltgrass at 700F is about twice that at 540F.
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