az1194 - Cooperative Extension Turf Irrigation Management...

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Cooperative Extension Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director, Cooperative Extension, College of Agriculture and Life Sciences, The University of Arizona. The University of Arizona College of Agriculture and Life Sciences is an equal opportunity employer authorized to provide research, educational information, and other services only to individuals and institutions that function without regard to sex, religion, color, national origin, age, Vietnam era Veteran’s status, or disability. Basics of Evaporation and Evapotranspiration 12/2000 AZ1194 Turf Irrigation Management Series: I T HE U NIVERSITY OF A RIZONA C OLLEGE OF A GRICULTURE T UCSON , A RIZONA 85721 Paul Brown Biometeorology Specialist This information has been reviewed by university faculty. ag.arizona.edu/pubs/water/az1194.pdf Turf Irrigation Management Series INTRODUCTION Local information on evapotranspiration (ET) is now readily available from on-site weather stations and/or public weather networks to assist turfgrass profession- als with irrigation management decisions. Proper uti- lization of ET information can provide accurate esti- mates of daily water use and thus can assist irrigation managers with the all important decisions of when to apply water and how much water to apply. The con- cept of ET can be confusing and often is presented in a highly technical manner. The objective of this and sub- sequent bulletins in the Turf Irrigation Management Se- ries is to simplify the subject of ET and thereby increase the effective utilization of ET in irrigation management. This bulletin provides some basic background on the related subjects of evaporation and evapotranspiration. EVAPORATION Water can exist in the natural environment in three different forms or states — solid (ice), liquid and gas. The process by which water changes from a liquid to a gas is known as evaporation. We are all familiar with liquid water as we drink, bath and irrigate with it daily. The gaseous form of water, known as water vapor, is less familiar since it exists as an invisible gas. How- ever, we all have a feel for water vapor during the late summer months when it is called by the more common name of humidity. To the irrigation manager, the most important points about evaporation are 1) it is the pro- cess by which most of the liquid water we apply as irrigation leaves vegetation and 2) that evaporation requires energy (Fig. 1). Two common household items — the clothes dryer and the evaporative cooler — clearly show the energy requirement of evaporation. In the case of the dryer, a gas burner or an electric heating element provides the heat energy required to evaporate water from the wet clothes. The evaporative cooler works in a somewhat opposite manner. Energy stored in the hot, dry, outside air is consumed by the evaporation process as the air passes through the wet pads. This energy consump-
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This note was uploaded on 04/04/2008 for the course NATS 101 taught by Professor Allister during the Spring '08 term at Arizona.

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az1194 - Cooperative Extension Turf Irrigation Management...

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