A Study of Fitting a Swamp Meadow Ecosystem Evapotranspiration to a Model Based on the Penman-Monteith Equation

Feng Li,Bin Wang

doi:10.1155/2015/315708

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 (kc), which was calculated as the ratio of the measured actual ET (ETafrom the eddy covariance (EC) system) to the reference ET (ET0from 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 ofkcexhibited significant seasonal variations within the range 0.3–1.0 with a meankcof 0.55 during the growing season. The dailykcshowed a linear increase withRnandTaand a linear decrease with the VPD. With respect to the biotic factors, the biomass exhibited a significant positive correlation withkc. Thus, a dailykcmodel is developed as a function of the VPD,Rn,Ta, and biomass.

Highlights

The hydrologic balance of terrestrial ecosystems is an important determinant of ecosystem structure, function, and productivity [1]
This study aimed to achieve the following objectives: (1) use the Food and Agriculture Organization- (FAO-)P-M model and eddy covariance system to explore the dynamics of the actual ET and reference ET changes in the swamp meadow ecosystem of the Sanjiangyuan Region and (2) derive a suitable kc-based model of the swamp meadow ecosystem by determining how kc values vary with changes in meadow climate and vegetation and by establishing the relationships between kc and the factors
The annual reference ET of the examined swamp meadow was 900.2 mm, which was significantly higher than the actual ET of 425.8 mm

Summary

Introduction

The hydrologic balance of terrestrial ecosystems is an important determinant of ecosystem structure, function, and productivity [1]. Evapotranspiration (ET), which is the second largest water flux in the terrestrial hydrologic cycle, plays an important role in the maintenance of the water and energy balance of the ground surface [2]. Accurate ET estimation is significant to the regulation and management of hydrologic cycles in ecosystems and to scientific decisions regarding local ecological construction and production activities in agriculture and animal husbandry [3,4,5]. The Penman equation, which utilizes conventional meteorological data, is the most influential fitting equation for predicting ET. This equation was proposed in 1948 when Penman proposed a formula for calculating ET from a water surface, which considers radiant energy, air saturation deficit, wind speed, and other ETinfluencing factors. In 1990s, the Food and Agriculture Organization (FAO) of the United Nations amended the P-M model for the estimation of actual ET from farmland and grassland and recommended this modified model as a standard method for calculating ET [10]

Objectives

Methods

Results

Conclusion