Evapotranspiration in a desert environment

Abstract

The natural evapotranspiration rate in a desert environment was studied at a site near Silverbell, Arizona, as part of the Desert Biome Program. Evapotranspiration rates were measured directly using a monolith weighing lysimeter. Indirect determination of evapotranspiration rates by a water-balance analysis was made using two different methods to measure soil moisture. The soil moisture data were initially gathered directly using neutron probes, but during 1977 soil-water potential data measured with thermocouple psychrometers were translated into soil moisture information using a soil characteristic curve developed for the soil. The annual evapotranspiration rate that was measured or calculated was equivalent to the natural evaporation rate from bare soils. The annual precipitation was approximately equal to the water loss due to the annual evapotranspiration with little or no change in soil moisture storage between years. Peak evapotranspiration rates of 3-5 mm/day occurred only after rainfall events, while during dry periods the evapotranspiration rate approached zero.