Priestley-Taylor model coefficient in a typical Artemisia ordosica shrubland in Mu Us Sandy Land of northwestern China
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摘要:
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。 -
关键词:
- Priestley-Taylor模型系数 /
- 蒸散发 /
- 涡度相关法 /
- 半干旱区 /
- 油蒿
Abstract:ObjectiveEstimating 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. MethodThis 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. ResultThe 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, R2 was 0.57. ConclusionTherefore, the modified PT model can be used to accurately estimate evapotranspiration in arid and semi-arid regions. -
图 1 环境因子的季节变化
SWC30. 30 cm处土壤含水量；SWC10. 10 cm处土壤含水量。
Figure 1. Seasonal variations in environmental factors
SWC30, soil water content at 30 cm belowground; SWC10, soil water content at 10 cm belowground.
图 2 不同物候期内油蒿灌丛PT模型α系数季节变化
Figure 2. Seasonal changes of α coefficient of PT model in Artemisia ordosica shrubland during different phenological phases
图 3 白天(08:00—17:00)时段PT模型系数与相关因子在整个生长季内的相关关系
Figure 3. Correlations between the PT model coefficient and the related factors during the whole growing season in daytime (08:00-17:00)
图 4 PT模型系数常规值分别为1.26(a、b)和0.50(c、d)时蒸散发模拟值和实测值的比较与拟合
ET.实测值; ET1.26.系数为1.26的模拟值; ET0.50.系数为0.50的模拟值。图中虚线表示y=x。下同。
Figure 4. Comparison and relationship between measured evapotranspiration and the modelled one by the conventional PT model coefficients of 1.26 (a, b) and 0.50 (c, d)
ET, measured evapotranspiration; ET1.26, modelled evapotranspiration by coefficient of 1.26; ET0.50, modelled evapotranspiration by coefficient of 0.50. The dash line represents y=x in (b) and (d). The same below.
图 5 PT模型系数修正后蒸散发模拟值和实测值的比较(a)与拟合(b)
ET0.23.系数为0.23的模拟值。
Figure 5. Comparison and relationship between measured evapotranspiration and modelled one by corrected PT model coefficients
ET0.23, modelled evapotranspiration by coefficient of 0.23.
表 1 2014年油蒿物候期
Table 1. Phenophases of Artemisia ordosica in 2014
物候期
Phenophases日序
Day of year (DOY)展叶期
Leaf expansion period102~134 完全展叶期
Full leaf expansion period135~234 叶变色期
Leaf coloration period235~291 注：数据表示2014年中的第几天。Note: data is the ordinal date in a year. 
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