A study of fitting a swamp meadow ecosystem evapotranspiration to a model based on the Penman-Monteith equation

Abstract

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 (k c), which was calculated as the ratio of the measured actual ET (ET a from the eddy covariance (EC) system) to the reference ET (ET 0 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 k c exhibited significant seasonal variations within the range 0.3-1.0 with a mean k c of 0.55 during the growing season. The daily k c showed a linear increase with R n and T a and a linear decrease with the VPD. With respect to the biotic factors, the biomass exhibited a significant positive correlation with k c. Thus, a daily k c model is developed as a function of the VPD, R n, T a, and biomass.