黄土高原春小麦农田蒸散及其影响因素

Evapotranspiration and factors influencing evapotranspiration in the spring wheat farmland of China's Loess Plateau

蒸散与水循环、能量平衡密切相关,是黄土高原雨养农田生态系统最重要的水通量之一。准确测定半干旱区农田生态系统蒸散,对增强陆气相互作用的理解以及科学应对气候变化有重要意义。采用涡度相关技术对黄土高原春小麦农田生态系统蒸散进行了观测,利用气象梯度系统进行环境因子观测;分析了春小麦农田生态系统蒸散日、季动态及其环境影响因子。结果表明,黄土高原半干旱区春小麦农田生态系统蒸散呈早晚低、中午高的"单峰型"日变化特征;最大日峰值出现在8月(0.22mm/h)。生长季蒸散日峰值高于非生长季。春小麦农田最大日蒸散率值相对较低,这可能与该地区干旱少雨的气候特征有关。农田蒸散且具有明显的季节动态,与降水季节分布密切相关。7、8月份降水较多,月蒸散量较高。全年蒸散量(318.0 mm)略低于年降水量(332.3 mm);蒸散量与降水量比值为95.7%。非生长季蒸散量显著低于生长季(4—9月);二者之比为0.26。农田蒸散随土壤含水量和空气温度(低于26℃)增大呈指数增长趋势;随空气相对湿度、太阳辐射、风速增大呈先增大后降低的二次曲线变化趋势。净辐射是黄土高原半干旱区农田生态系统蒸散主要环境控制因子,土壤含水量次之。

Abstract： Evapotranspiration （ET） links water and energy cycles, and is one of the most important water fluxes in the rain- fed agroecosystem of the Loess Plateau, China. Accurate measurements of ET in this semi-arid agroecosystem are critical to gaining a better understanding the interactions between terrestrial ecosystems and atmosphere, and tackling climate change scientifically. This study was conducted at the Dingxi Arid Meteorology and Ecological Environment Experimental Station （DAMES） in 2010. The eddy covarianee system and microclimate gradient system were used to observe ET and environmental conditions, respectively. We analyzed the diurnal and seasonal dynamics of ET and environmental factors influencing ET throughout the spring wheat agroecosystem in the semi-arid Loess Plateau. The results showed that the diurnal variation of ET in this agroecosystem can be graphed as a line with a single-peak which occurs around noon with lower ET rates observed in the morning and evening; also, seasonal ET peaked in August （ 0.22 mm/h）. Daily peak ET values in the growing season were larger than those in non-growing season. During the observation period, the maximum daily ET rate of spring wheat farmland was relatively low, which may be related to the dry climatic conditions with low levels of precipitation typical of the semi-arid area of the Loess Plateau. ET varied significantly from season to season in the spring wheat agroecosystem and ET dynamics were closely related to the seasonal distribution of precipitation. Monthly ET peaked during July and August because relatively more rain was received during these two months. Annual ET （318.0 mm） in 2010 was slightly lower than annual precipitation （332.3 mm） ; the ratio of ET to precipitation was 95.7%. ET during the non- growing season was significantly lower than that during the growing season （ April to September）, with a ratio of non- growing season to growing season ET of 0.26. Total ET in the spring wheat agroecosystem increased exponentially with increases in either soil water content and/or air temperature （lower than 26 ℃ ）. ET responded to changes in relative humidity, solar radiation, and wind speed in a quadratic curve manner with a pattern of first increasing and then decreasing. Net radiation was the major environmental factor controlling ET in the semi-arid agroecosystem of the Loess Plateau, followed by soil water content.