Report on the Platte River Basin, Nebraska Level B Study

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Droughts have severely affected most of the basin at one time or another. The periods of 1887- 1896, 1924 -1927, 1934 -1941, and 1952 -1956 were particularly severe. However, droughts are not re- stricted to years with low annual rainfall. They have occurred in years with average total annual precipitation where the monthly distribution of rain- fall throughout the year did not follow the normal pattern. Figure 10 shows the normal monthly distribution of precipitation at Scottsbluff, North Platte, and Lincoln. s 4 w 3 c 2 0 - 0 c ° m n m c r n ° o w -�i ii 4 t 4, 4 U) 0 Z 0 SCOTTSBLUFF Figure 10 NORMAL MONTHLY PRECIPITATION c d L T N 1 W u p d 1i 2 4 `t 13 4 y 0 2 O NORTH PLATTE About 70 percent of the average annual precip- itation normally falls during the crop growing season from April through September. In some years, however, rainfall in the summer months is negligible and in other years it is several times the normal amount. Two dry months in summer will likely result in dryland crop failure, and one wet month in fall may prevent or seriously delay crop harvest. TEMPERATURE Air temperatures in the basin may vary widely from day to day; however, mean temperatures on a monthly basis vary only five to ten degrees be- tween widely separated areas. During the period 1921 to 1965, the frost -free period between the last spring and first fall temper- ature of 32 degrees ranged from a low of about 130 days in the west to a high of about 170 days in the eastern part of the basin. WIND c a r a . ii 2 4 y -7i Q m 0 Z LINCOLN College View Although this study looked mainly at wind effects on evaporation and erosion, wind also affects human comfort and safety, particularly in the use of open water for hunting, swimming, and boating. Winds in the basin are generally from a southerly direction in the warmer seasons and from a northerly direction in winter. Winds of high velocity normally are of short duration and asso- ciated with severe thunderstorms, but persistent winds strong enough to cause soil blowing and to adversely affect outdoor activities are common. , EVAPORATION AND TRANSPIRATION Moisture moves to the atmosphere by evapora- tion from water surfaces and the soil, and from plants by transpiration. The combined action of , both phenomona is termed evapotranspiration. In the Platte Basin the average annual rate ranges from 2.1 feet in eastern portion to 2.4 in the central portion and 2.3 in the west. , s , 4 Vi d t 3 c 2 1 , 0 i Although this study looked mainly at wind effects on evaporation and erosion, wind also affects human comfort and safety, particularly in the use of open water for hunting, swimming, and boating. Winds in the basin are generally from a southerly direction in the warmer seasons and from a northerly direction in winter. Winds of high velocity normally are of short duration and asso- ciated with severe thunderstorms, but persistent winds strong enough to cause soil blowing and to adversely affect outdoor activities are common. , EVAPORATION AND TRANSPIRATION Moisture moves to the atmosphere by evapora- tion from water surfaces and the soil, and from plants by transpiration. The combined action of , both phenomona is termed evapotranspiration. In the Platte Basin the average annual rate ranges from 2.1 feet in eastern portion to 2.4 in the central portion and 2.3 in the west. ,