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<br />2-11 <br /> <br /> <br />OO:ZD5'Z <br />'.' ~'.""_ ,~A, -'''.;i <br /> <br />Wind <br /> <br />Although this study looked mainly at wind effects on evapo- <br /> <br />ration and erosion, wind also affects human comfort and safety, <br /> <br />particularly in the use of open water for hunting, swimming, and <br /> <br />boating. Winds in the basin are generally from a southerly di- <br /> <br />rection in the warmer seasons and from a northerly direction in <br /> <br />winter. Winds of high velocity normally are of short duration <br /> <br />and associated with severe thunderstorms, but persistent winds <br /> <br />strong enough to cause soil blowing and to adversely affect out- <br /> <br />door activities are common. <br /> <br />Evaporation and Transpiration <br /> <br />Moisture moves to the atmosphere by evaporation from water <br /> <br />surfaces and the soil, and from plants by transpiration. The <br /> <br />combined action of both phenomona is termed evapotranspiration. <br /> <br />In the Platte Basin the average annual rate ranges from 2.1 feet <br /> <br />in the eastern portion, 2.4 in the central portion and 2.3 in the <br /> <br />west. <br /> <br />Evaporation from free water surfaces occurs from lakes, <br /> <br />storage reservoirs, streams, and canals. The average annual <br /> <br />gross and net lake evaporation across the basin is shown in <br /> <br />figure 2-8. Average precipitation is the difference between gross <br />and net evaporation. The rate of evaporation is dependent largely <br /> <br />on wind velocity, temperature, and relative humidity. Many reser- <br /> <br />voirs and ponds in the basin are comparatively shallow and the re- <br /> <br />sulting large surface area combined with the high evaporation rates <br /> <br />common to the Great Plains causes considerable water loss. <br />