Estimation of evapotranspiration in Eucalyptus plantation and mixed forests based on air temperature and humidity

Abstract

Soil evaporation, Air temperature and humidity inside and outside the forest and river flows were continually monitored in eucalyptus plantations (EU) and coniferous broadleaved mixed forests (MFs) to investigate the reasons for the decreased runoff recorded in EU. The applicabilities of four estimation methods based on air temperature and humidity were evaluated and verified. Our results show that: (1) the average annual solar radiation penetration rate of the EU canopies was 1.75 times that of the MFs canopies, and temperatures were lower inside the two forests than outside the forests. The daily average temperatures inside the EU and MFs were 20.7 ℃ and 20.8 ℃, respectively, which were 1.5 ℃ and 1.4 ℃ lower than those outside the forests. The daily average relative humidity was 0.8% higher in the MFs than in the EU. (2) The evapotranspiration of EU and MFs accounted for 80.2% and 76.3% of the total rainfall respectively, of which the soil evaporation was 12.8% and 8.9% respectively, and the runoff production coefficients were 0.198 and 0.237 respectively. The main reason for the decrease of the EU production was that soil evaporation in EU was 43.8% higher than that in MFs. (3) The deviation of EU and MFs evapotranspiration (ET0) from the measured values was estimated by the ET0Valian(T, RH) and ET0Alt/rs(T, RH) methods as less than 10%. (4) Using the product of the extraterrestrial solar radiation and the surface solar emissivity of the forest instead of the extraterrestrial solar radiation in these four formulas, the variation trend of the estimated forest soil evaporation was highly similar to the measured value. ET0Valian(T, RH) and ET0Alt/rs(T, RH) had the highest accuracy in soil evaporation estimation (2.0–3.4% lower than the measured values). The results provide a theoretical basis for studying the ecohydrology of subtropical plantations in the Northern Hemisphere.