Radiation Balance and Soil Water Evaporation of Bare Pullman Clay Loam Soil

by T. A. Howell,
J. L. Steiner,
S. R. Evett,
A. D. Schneider,
K. S. Copeland,
D. A. Dusek,
A. Tunick,



Document Type: Proceeding Paper

Part of: Management of Irrigation and Drainage Systems: Integrated Perspectives

Abstract:

Radiation and energy balance components and soil water evaporation were measured for a bare Pullman clay loam soil at Bushland, TX during the 1992 spring and summer as the soil dried following irrigation and rain. Bare soil albedo for the Pullman soil varied from 0.11 to 0.13 for wet to drying conditions in May. However, during the July measurement period following a rain event, soil albedo increased to 0.18 upon drying due to the formation of a surface crust and smoothing of the surface by the rain. Measured net radiation agreed with the measured short- and long-wave radiation components. Emitted ground long-wave radiation measured by a pyrgeometer was slightly greater than computed emitted radiation using surface temperature and the Stefan-Boltzmann equation. Sky emissivity was influenced by clouds; however, for clear sky conditions, a Brunt type emissivity equation based on screen-level vapor pressure was more representative than equations based on screen-level air temperature. For wet conditions, the latent heat flux accounted for over 80% of net radiation while for the drying soil latent heat flux was less than 25% of net radiation. Three models of soil evaporation all estimated daily evaporation accurately for these conditions. A mechanistic soil water-energy simulation model, ENWATBAL, accurately estimated net radiation and soil water evaporation.

Subject Headings: Soil water | Evaporation | Radiation | Computer models | Clays | Model accuracy | Solar radiation

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