Mono Basin: Evaporation

Vorster describes "pan" studies to learn the average evaporation rate in the Mono Basin. By placing a pan of fresh water in the field, scientists observe the loss of water and infer the rate of evaporation over the course of a year. (Sometimes the pan loses water from high winds, but the scientists would not publish these results). Vorster lists 15 different studies in the Mono Basin. The estimates range from around 39 to 51 inches/year. His own estimate is 45 inches/yr.

You have read in chapter 4 that the saline waters of Mono Lake evaporate more slowly than fresh water. With 1980 conditions, for example, Mono Lake contained around 90,000 parts per million of disolved solids. The lake's specific gravity was 1.075. Based on studies of the Great Salt Lake, Vorster believes that the dissolved solids would lower the rate of evaporation by 5.4%. under these conditions. Vorster incorporates the salinity effect on evaporation based on studies by Lee (1934) and Loeffler (1977). He uses the specific gravity of the water in Mono Lake as the measure of the lake's salinity, and he estimates the specific gravity based on the assumption that 230 million tons of solids are dissolved in the lake.

Evaporation is one of the largest flows in the basin. Suppose the surface area were 39 thousand acres; the fresh water evaporation rate were 45 inches/yr (3.75 feet/yr); and salinity lowered the evaporation rate by around 5%,. Under these conditions, we would expect 139 KAF/yr to leave the basin through evaporation:

139 KAF/yr = 39 Kacres * (3.75 ft/yr) * (95%)