| Summary: | To accurately estimate the magnitude and seasonal dynamics of evapotranspiration (ET) over an important a swamp meadow in the Fenghuoshan permafrost region, we employed the Food and Agriculture Organization- (FAO-) Penman-Monteith (P-M) model. The model was also used to investigate changes in the crop coefficient (kc), which was calculated as the ratio of the measured actual ET (ETa from the eddy covariance (EC) system) to the reference ET (ET0 from the P-M model). The results indicated a reference ET of 900 mm/year from the swamp meadow ecosystem, which was significantly higher than the actual ET (426 mm/year). The reference ET peaked from April to July, while the actual ET was primarily in growing season. The value of kc exhibited significant seasonal variations within the range 0.3–1.0 with a mean kc of 0.55 during the growing season. The daily kc showed a linear increase with Rn and Ta and a linear decrease with the VPD. With respect to the biotic factors, the biomass exhibited a significant positive correlation with kc. Thus, a daily kc model is developed as a function of the VPD, Rn, Ta, and biomass.
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