Yang Fulin, Zhang Qiang, Wang Runyuan, Zhou Jing
Key Laboratory of Arid Climatic Change and Reducing Disaster of Gansu Province, Key Open Laboratory of Arid Climatic Change and Disaster Reduction of China Meteorological Administration (CMA), Institute of Arid Meteorology, CMA, Lanzhou, China.
State Key Laboratory of Grassland Agro-ecosystems, College of Pastoral Agriculture Science and Technology, Lanzhou University, Lanzhou, China.
PLoS One. 2014 Jun 18;9(6):e100031. doi: 10.1371/journal.pone.0100031. eCollection 2014.
Evapotranspiration (ET) is an important component of the surface energy balance and hydrological cycle. In this study, the eddy covariance technique was used to measure ET of the semi-arid farmland ecosystem in the Loess Plateau during 2010 growing season (April to September). The characteristics and environmental regulations of ET and crop coefficient (Kc) were investigated. The results showed that the diurnal variation of latent heat flux (LE) was similar to single-peak shape for each month, with the largest peak value of LE occurring in August (151.4 W m(-2)). The daily ET rate of the semi-arid farmland in the Loess Plateau also showed clear seasonal variation, with the maximum daily ET rate of 4.69 mm day(-1). Cumulative ET during 2010 growing season was 252.4 mm, and lower than precipitation. Radiation was the main driver of farmland ET in the Loess Plateau, which explained 88% of the variances in daily ET (p<0.001). The farmland Kc values showed the obvious seasonal fluctuation, with the average of 0.46. The correlation analysis between daily Kc and its major environmental factors indicated that wind speed (Ws), relative humidity (RH), soil water content (SWC), and atmospheric vapor pressure deficit (VPD) were the major environmental regulations of daily Kc. The regression analysis results showed that Kc exponentially decreased with Ws increase, an exponentially increased with RH, SWC increase, and a linearly decreased with VPD increase. An experiential Kc model for the semi-arid farmland in the Loess Plateau, driven by Ws, RH, SWC and VPD, was developed, showing a good consistency between the simulated and the measured Kc values.
蒸散（ET）是地表能量平衡和水文循环的重要组成部分。本研究采用涡度相关技术测量了黄土高原半干旱农田生态系统2010年生长季（4月至9月）的蒸散量。研究了蒸散量和作物系数（Kc）的特征及其环境调控因素。结果表明，各月潜热通量（LE）的日变化均呈单峰型，其中8月LE峰值最大（151.4 W m(-2)）。黄土高原半干旱农田的日蒸散速率也呈现明显的季节变化，最大日蒸散速率为4.69 mm d(-1)。2010年生长季的累积蒸散量为252.4 mm，低于降水量。辐射是黄土高原农田蒸散的主要驱动因素，解释了日蒸散量88%的变化（p<0.001）。农田Kc值呈现明显的季节波动，平均值为0.46。日Kc与其主要环境因子的相关分析表明，风速（Ws）、相对湿度（RH）、土壤含水量（SWC）和大气水汽压差（VPD）是日Kc的主要环境调控因子。回归分析结果表明，Kc随Ws的增加呈指数下降，随RH、SWC的增加呈指数上升，随VPD的增加呈线性下降。建立了由Ws、RH、SWC和VPD驱动的黄土高原半干旱农田经验Kc模型，模拟值与实测值具有较好的一致性。
