Estimating Diurnal Variation of Soil Heat Flux for Alfalfa and Grass
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Soil heat flux (G) is an important component of evapotranspiration (ET) modeling,
especially for estimating hourly ET values. Meteorological and agronomic measurements were
made at Kimberly, Idaho, with the purpose of establishing relationships to estimate the diurnal
variations of soil heat flux for alfalfa and grass. For alfalfa, the relationship between G and net
radiation (Rn) presented pronounced hysteresis effects, which decreased with increasing plant
cover. Empirical equations to estimate diurnal variation of G from Rn and plant height (h) were
derived. For low cover conditions, including radiometric surface temperature (Tc) improved the
performance of the model. For grass, the hysteresis effects were not as pronounce as for
alfalfa. Acceptable relationships were found between G and Rn, and also between G and Tc (r
2
˜
0.90) for plant heights between 0.1-0.2 m. An improved model (r
2
= 0.94) was obtained by
including both Rn and Tc in the regression model.