Effects of climatic extremes on ground water in western Utah, 1930-2005

Climatic extremes affect ground-water levels and quality in the basins of western Utah. The five droughts since 1930: 1930-36, 1953-65, 1974-78, 1988-93, and 1999-2004—resulted in much-less-than-average recharge, and the pronounced wet period of 1982-86 resulted in much-greater-than-average recharge. Decreased recharge lowered the ground-water level, and increased recharge raised it. These changes were largest in recharge areas—in discharge areas the water level is relatively constant and the primary effect is a change in the discharge area—smaller during a drought and larger during a pronounced wet period.

The largest part of water-level change during climatic extremes, however, is not a result of changes in recharge but is related to changes in ground-water withdrawal. During a drought withdrawals increase to satisfy increased demand for ground water, especially in irrigated areas, and water levels decline. During a pronounced wet period, withdrawals decrease because of less demand and water levels rise. The amount of water-level change in representative observation wells in a basin is generally proportional to the basin’s withdrawal. In undeveloped Tule Valley, water-level changes related to climatic extremes during 1981-2005 are less than 2 feet. In Snake Valley (small withdrawal), Tooele Valley (moderate withdrawal), and Pahvant Valley (large withdrawal), water-level declines in representative wells from 1985-86 to 2005 were 13.4, 23.8, and 63.8 feet, respectively.

Ground-water quality is also affected by climatic extremes. In six irrigated areas in western Utah, water-level decline during drought has induced flow of water with large dissolved-solids concentrations toward areas of pumping, increasing the dissolved-solids concentrations in water sampled from observation wells. During the 1982-86 wet period, increased recharge resulted in a later decrease in dissolved-solids concentrations in three basins.