3.1 Seasonal variation of measured ET and environmental variables
The measured ET showed a clear seasonal pattern, the growing season ET was significantly higher than that in the non-growing season (P <0.05) (Fig.2a). The average measured daily ET during the study period was 2.62±0.12 mm d-1, with average daily measured ET of 4.17±0.13 mm and 0.65 ± 0.06 mm d-1 (here and throughout the remainder of the paper, values are expressed as mean ± 1 SD) during the growing season and non-growing season, respectively (Fig.2a). Environmental variables showed a similar seasonal pattern, except for VPD, with the maximum and minimum values in the growing season and non-growing season. The average daily Rn, Rs and Ta during the growing season were 11.07 ± 0.27 MJ m-2, 20.80 ± 0.38 MJ m-2 and 10.18±0.23 ℃, respectively (Fig.2b,c and d). The relative humidity peaked in August (80%), with an average of 62.91% over the whole study period (Fig.2f). The average daily VPD peaked in May (0.65 kPa), with an average of 0.45 kPa over the whole study period (Fig.2e).