Abstract
An empirical model for estimating the daytime (07-16h) mean Bowen ratio, of which independent variables were air temperature (T), relative humidity (RH) and soil moisture tension at 15cm depth (PF), was made using measured data from a sugar beet field. The estimate error of the model was determined by the data measured in another sugar beet field. The standard estimate error of daytime evapotranspiration (E) was also investigated. Calculation from the model showed that an increase in T of 5°C, a decrease in RH of 9% and a decrease in PF of 0.3 induce an increase in E of about 5%, when the Bowen ratio is about 0.3. It is also indicated that the influence of climatic change on evapotranspiration is larger in regions where the soil moisture content is higher.
