毛乌素沙地油蒿灌丛Priestley-Taylor模型系数研究

Priestley-Taylor model coefficient in a typical Artemisia ordosica shrubland in Mu Us Sandy Land of northwestern China

【目的】基于半经验半理论的Priestly-Taylor模型(PT)估算蒸散发(ET)时,主要依赖于精确确定该模型系数α在特定研究区内的适宜值,本研究就该模型系数α的适用性进行了本地化研究,以便更准确地估算干旱半干旱区的蒸散发。【方法】在中国西北干旱地区毛乌素沙地的一个生长季内,采用涡度协方差技术并结合气象数据信息,监测研究区典型油蒿灌丛地的水、热交换传输过程,以分析PT模型系数α的季节变化特征并确定其本地化估算参考值。【结果】在季节变化过程中,实际PT模型系数α整体变化较明显,展叶期内α系数呈单峰型变化趋势,完全展叶期和叶变色期内的α系数变化不明显;日均α系数最大值为0. 66,最小值为0. 03,全生长季α系数均值为0. 23。油蒿生长季内α系数与冠层导度和饱和水汽压差呈对数正相关;土壤含水量(30 cm处)以及叶面积指数与α系数均为正相关关系。在季节变化过程中,PT模型常规系数α=1. 26确定的蒸散量(ET1. 26)估算值以及根据逐日温度和2 m高度处风速资料计算的PT模型系数α=0. 50确定的蒸散量(ET0. 50)估算值均显著大于实测蒸散发。改进的PT模型系数的本地化推荐适宜值为0. 23,并且通过修正后的PT模型估算ET与实测值之间存在较好的一致性,线性斜率为0. 72,R2为0. 57。【结论】因此,修正的PT模型显著提高干旱半干旱区植被蒸散发估算精度,为区域植被水文过程模型提供支持。

[Objective] Estimating evapotranspiration (ET) based on the semi-empirical and semi-theoretical Priestly-Taylor model (PT) mainly relies on accurately determining the appropriate value of the model coefficient α in a specific study area. This study expored the applicability of the model coefficient α. Localization studies have been conducted to more accurately estimate evapotranspiration in arid and semi-arid regions.[Method] This paper used the eddy covariance technique combined with micro-meteorological data to monitor the water and heat transfer processes of a typical Artemisia ordosica shrubland in growing season in Mu Us Sandy Land of northwestern China to quantify the seasonal variations in α coefficients.[Result] The results showed that the actual α coefficient had significant seasonal variations, peaking during the leafing period, and remaining relatively plateau during expanded leaf period and the leaf discoloration period. The maximum α coefficient was 0.66 and the minimum value was 0.03, averaging 0.23 in growing season. There was a logarithmic positive correlation between α coefficient and canopy conductance and saturated vapor pressure difference in the growing season. Soil water content (30 cm belowground) and leaf area index were positively correlated with α coefficient. Evapotranspiration estimated from the PT model with α=1.26 and with α=0.50, which was calculated from the wind speed data at 2 m height, was significantly larger than the measured evapotranspiration. The recommended localization value of the improved PT model coefficient α was 0.23, which gave better estimation of ET, linear gradient was 0.72, R^2 was 0.57.[Conclusion] Therefore, the modified PT model can be used to accurately estimate evapotranspiration in arid and semi-arid regions.