The Energy Balance of Non-Uniform Soil Surfaces

Abstract

A ?fluxometer? has been developed for estimating the fluxes of latent and sensible heat from bare soil and short grass in any type of terrain. The fluxometer consists of two polyethylene-covered tunnels 50 cm long, 30 cm wide, and 6 to 12 cm high. The floor of one is exposed to the soil surface; the floor of the other is covered with plastic, as a control. The latent and sensible heat fluxes can be determined from the wet-and dry-bulb temperatures of the air entering and leaving the exposed tunnel at a known rate. A comparison of hourly evaporation rates measured simultaneously with the fluxometer and with three precision weighing-type lysimeters at Tempe, Ariz., showed that the fluxometer usually gave lower evaporation rates than the lysimeters. A second experiment was conducted in a dry river channel in southeastern Arizona. Evaporation rates were measured during 18 days and agree well with estimates by other investigators. For 33 hourly periods, during which all energy balance components were measured, the average absolute error was 2.4 ly hr?1; the average relative error was 11.0 per cent.