A water budget for Great Salt Lake, Utah, was computed with 1-month intervals for the 46-year period of 1931-76. This budget updates previous computations for 1931-73, The updating was made on the basis of additional data collected during 1974-76. The storage change (ΔS) during each month was computed from a budget of surface inflow (Is), ground-water inflow (Ig), precipitation on the lake surface (Ip), a calibration parameter (Ium) representing the net deficit between the estimated net inflows and the observed net inflows as computed from the observed altitude hydrograph, and outflow from evaporation (Oe), where ΔS= Is + Ig + Ip+ Ium - Oe.
Based on additional pan-evaporation data collected at six sites around the perimeter of the lake, estimates of evaporation rates were reduced about 8 percent. The annual evaporation ranged from about 2.1 to 3.9 million acre-feet (2,600 to 4,800 cubic hectometers) and averaged 2.9 million acre-feet (3,576 cubic hectometers).
Based on addie6nal surface-inflow data collected during 1974-76, the annual surface inflow to the lake for 1931-76 ranged from 705,200 (1934) to 3,767,000 (1971) acre-feet (870 to 4,645 cubic hectometers) and averaged 1,926,000 acre-feet (2,375 cubic hectometers).
No changes were made to the 1931-73 estimates of precipitation (Ip) on the lake surface or to the estimate of ground-water inflow (Ig). These averaged 870,000 and 75,000 acre-feet (1,072 and 92.5 cubic hectometers) per year, respectively.
The total annual inflow to Great Salt Lake during 1931-76 (Is + Ig + Ip+ Ium) ranged from about 1.3 (1961) to 5.0 (1971 and 1975) million acre-feet (1,603 to 6,165 cubic hectometers) and averaged 2.9 million acre-feet (3,575 cubic hectometers).
Some minor revisions were made to the digital-computer model used to compute the water and salt balance for the Great Salt Lake. Most revisions involved adaption to the longer base period of 1931-76 and revision of the water budget as a result of changes in estimates of evaporation and surface inflow.
