Abstract:

The “Three temperatures (3T) model” is a recently proposed method to estimate evapotranspiration and evaluate environmental quality. Because the key components for this model are three temperature variables, it is referred to as the “3T model”. This study discusses the procedures used to estimate evaporation, and model is verified based on a theoretical analysis and experimental data.

By introducing a reference dry soil (a soil without evaporation), soil evaporation (E) can be calculated by:

LE=R_n-G-(R_nd-G_d) \frac{T_s-T_a}{T_{\mathit{sd}}-T_a}

where L is latent heat of vaporization, R_n and R_nd are the net radiations of drying and dry soil, respectively. G and G_d are soil heat fluxes in drying soil and dry soil, respectively. T_s and T_sd are the surface temperatures of drying soil and dry soil, respectively. T_a is the air temperature. Results of the experimental work indicated that the energy fluxes over drying and dry soil were significantly different. Soil heat flux and net radiation on the dry soil are smaller than that on the drying soil, whereas the heat flux of the dry soil is higher than that of the drying soil. Typically, the dry soil surface temperature was higher than that of the drying soil surface temperature and the drying soil surface temperature was higher than the air temperature. Results of a field experiment showed that the measured E (using of a weighing lysimeter) and the calculated E using the 3T model agreed with each other and the mean absolute error (MAE) between them was 0.17 mm·d^-1 with a regression coefficient of r²=0.88. Furthermore, by using the temperature measured by infrared thermometers, the MAE between measured and estimated evaporation was 0.15 mm·d^-1 with a regression coefficient of r²=0.94. These results showed that evaporation as estimated by 3T model is accurate. The main advantage of the 3T model is that only a few parameters (temperature, net radiation and soil heat flux) are required. Soil surface resistance, aerodynamic resistance, and other empirical parameters are not necessary.

Key words: 3T Model, Dry soil, Drying soil, Soil evaporation