干旱区人工枣林蒸散及植株蒸腾的模型模拟

Model Simulation of Evapotranspiration and Plant Transpiration in Planted Jujube Forests in Arid Zones

【目的】选择适合的模型模拟干旱区枣林蒸散量及植株蒸腾量,为干旱区枣林制定合理灌溉制度、灌溉决策提供理论依据。【方法】SIMDual_Kc模型以双作物系数法为基础,引入作物密度系数K_(d),适用于稀疏冠层的果树或高频灌溉的作物。利用干旱区人工枣林2年涡度协方差(Eddy covariance,EC)技术实测蒸散量、热脉冲法实测植株蒸腾量,验证SIMDual_Kc模型的适用性和率定模型参数,并根据实测数据预设灌溉频率,模拟不同灌溉频率对蒸散的影响。【结果】SIMDual_Kc模型模拟干旱区人工枣林生育期内的蒸散量、植株蒸腾量精度较高,蒸散量模拟精度:决定系数R^(2)=0.57-0.60,模型一致性指数d=0.86-0.87,模型有效性NSE=0.51-0.55;植株蒸腾量模拟精度:R^(2)=0.73-0.77,d=0.91-0.92,NSE=0.62-0.64;蒸散量、植株蒸腾量的实测值和模拟值有较好的一致性。适用于干旱区人工枣林的SIMDual_Kc模型参数:基础作物系数K_(cb ini)=0.18,K_(cb mid)=0.7,K_(cb end)=0.7;蒸发层深度Z_(e)=0.15 m,总蒸发水量TEW=18 mm,易蒸发水量REW=9 mm,土壤水分消耗比率p=0.5。情景预测显示,在总灌溉量相同时,不同的灌溉频率对土壤蒸发量影响较大,对植株蒸腾量影响较小;土壤蒸发量随着灌溉频率的增大而变大,土壤表层含水率对土壤蒸发量的影响较大。【结论】SIMDual_Kc模型模拟干旱区人工枣林蒸散量、植株蒸腾量的精度较高,选择合适的滴灌频率对节水很重要。

【Objective】Ziziphus jujuba is a tree species with both ecological and economic benefits and has been successfully introduced to Xinjiang,China over the last two decades.Management of forest water consumption in arid zones requires estimations of evapotranspiration,which this study aimed to address through the use of the SIMDual-Kc model.【Method】The model was parameterized and its applicability to dryland plantation economic forests was verified through measures of evapotranspiration and plant transpiration rate by two-year eddy covariance and a pin-stem flow meter,respectively.Evapotranspiration and plant transpiration were simulated under different irrigation frequencies,preset according to the 2-year measured data.【Result】The SIMDual_Kc model was able to provide estimates of evapotranspiration and plant transpiration during the reproductive period that showed good consistency with measured data.When compared against measured data,the model simulations of evapotranspiration obtained determination coefficient(R^(2)),index of agreement(d),Nash Sutcliffe Efficiency(NSE),and Standard Deviation Ratio(RSR)goodness-of-fit values of 0.57–0.60,0.86–0.87,0.51–0.55,and 0.67–0.70,respectively,whereas those of simulated plant transpiration were 0.73–0.77,0.91–0.92,0.62–0.64,and 0.60–0.61,respectively.The parameters of the SIMDual-Kc model were:Basalt crop coefficient K_( cb ini)=0.18,K_( cb mid)=0.7,K_( cb end)=0.7,Depth of evaporation layer Z _(e)=0.15 m,Total evaporation water TEW=18 mm,Readily evaporable water REW=19 mm,and Soil water consumption ratio P=0.5.Model scenario analysis showed that under a constant total irrigation depth,different irrigation frequencies had greater and smaller effects on soil evaporation and plant transpiration,respectively and soil evapotranspiration increased with increasing irrigation frequency,indicating that soil surface water content had a greater effect on soil evapotranspiration.【Conclusion】The SIMDual-Kc model provided accurate estimates of evapotranspiration and plant transpiration of planted Jujube forests in arid zones.The result of this study can provide a theoretical basis for formulating reasonable drip irrigation systems,irrigation decisions,and for agricultural water conservation in arid zones.