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2-16 I I I I I I I I I I I I I I I I I I I woodlands occupy another 26.3 million acres. Forest and woodland and pasture and range acreages are expected to decline slightly during the next quarter century, contributing to a moderate overall decline in total agricultural lands. Dryland farming is the second largest type of agricultural land use in the basin, exceeded only by pasture and rangelands. These nonirrigated croplands are projected to increase over the next 25 years by some 2 percent from their current level of nearly 90 million acres, while pasture and rangeland acreage may decline substantially. Irrigated cropland, estimated at 11.4 million acres in 1975, constitutes about 4 percent of the present agricultural total. Irrigation is projected to be applied to an additional 2.8 million acres by 1985 and to 5.9 million acres by 2000, covering more than 17 million acres by the year 2000. The basin's urban and transportation lands are expected to expand from the present 7.4 million acres by 10 percent by 1985, and by 23 percent by the year 2000. Estimates of Missouri Basin land and water acreage for 1975, 1985, and 2000 are summarized in table 2-2. WATER RESOURCES CHARACTERISTICS The Missouri River Basin is, in general, well endowed with surface and ground water resources. However, the occurrence and availability of water is highly variable, subjecting portions of the basin to recurrent local and seasonal shortages. Surface Water Availability Precipitation annually provides more than 500 million acre-feet of water. Infiltration and evaporation deplete a large amount of this naturally occurring moisture. Runoff entering the streams varies widely across the basin, ranging annually from less than an inch in parts of the plains to more than 12 inches in the mountains and the humid southeast. This runoff would account for an