基于蒸渗仪的冬小麦-夏玉米ET估算模型特征参数研究

为快速准确估算农田蒸散量,利用24个群集式蒸渗仪,在国家节水灌溉北京工程技术研究中心大兴节水灌溉试验站进行了两年的灌溉试验,获得冬小麦-夏玉米生育期的日内冠气温差和实际日蒸散量(ET_a)等数据,对不同水分处理下的S-I蒸散量估算模型进行率定及验证,并分析模型特征参数a、b的变化规律及两者的差异。结果表明:冬小麦的S-I模型特征参数a在日间随时间变化先增大、后减小,在严重水分胁迫处理时a为负值、且数值较小,其余灌溉处理时参数a由正值逐渐变化至负值;不同灌水处理b均为负值,充分灌溉处理时b在日间随时间变化逐渐增大,严重水分胁迫处理时b相对较大,日间变化趋势不稳定。水分胁迫对夏玉米模型参数的影响程度低于冬小麦,特征参数a均为正值,参数b均为负值,且随时间变化逐渐增大;水分胁迫处理时b变化范围明显小于其他两个处理,干旱处理特征参数日间变化较大。冬小麦与夏玉米不同处理之间模型参数a、b变化差异较大,但冠层温度和空气温度差T_c-T_a与日蒸散量和日净辐射量差ET_d-Rn_d间拟合精度都在13:00时最高,此时充分灌溉冬小麦和夏玉米的模型参数a、b分别为1.082、-1.127和1.588、-1.363。利用率定的S-I模型计算冬小麦和夏玉米主要生育期ET_d与实测ET_a之间的决定系数R~2均在0.7以上,均方根误差RMSE均小于0.89 mm/d,一致性系数d均在0.9以上。尤其是充分灌溉处理的数据间R~2和d均较高,RMSE小于其他处理,说明水分胁迫影响模型的估算精度,S-I模型能够更准确地估算水分胁迫较少农田的蒸散量。

Feature Parameters of Evapotranspiration Estimation Model for Winter Wheat and Summer Maize Based on Lysimeter Monitoring System

Accurate and rapid estimation of evapotranspiration in farmland is significant for precise irrigation management and optimal allocation of water resources.Based on 24 cluster lysimeters,irrigation experiments of winter wheat and summer maize were carried out in 2019—2020,in Daxing Water-saving Irrigation Experimental Station of IWHR,Beijing.Daily data of crop canopy temperatures(T c)and air temperatures(T a),and daily evapotranspiration measured by lysimeter(ET a)were observed,to calibrate and validate the named S I model,which was simple and valid to estimate field crops ET.Then the changes and values of feature parameters of S I model,a and b,were analyzed and concluded for winter wheat and summer maize,respectively.Results showed that for winter wheat,the characteristic parameter a of the S I model was increased firstly and decreased subsequently with time change in day.In the case of severe water stress,a was negative and the value was small,and in the case of other irrigation treatments,a was positive and gradually changed to negative.The characteristic parameter b in different irrigation treatment was negative.The parameter b of adequate irrigation treatment was gradually increased with time changes in the day,while the value of severe water stress treatment was relatively large,and the trend in day was unstable.For summer maize,the effect of water stress on model parameters was lower than that of winter wheat.The characteristic parameter a was positive,while the parameter b was negative,which was gradually increased with time.The variation range of parameter b under water stress treatment was significantly smaller than that under other two treatments.The characteristic parameters of drought treatment was changed greatly within days.Model parameters a and b varied greatly between winter wheat and summer maize under different treatments,but the fitting accuracy of(canopy temperature T c-air temperature T a)and(daily evapotranspiration ET d-daily net radiation Rn d)was the highest at 13:00.At this time,model parameters a and b of full irrigation were 1.082 and-1.127 for winter wheat,1.588 and-1.363 for summer maize,respectively.The determination coefficient(R 2)and consistency coefficient d were above 0.7 and 0.9 between the model ET d and measured ET a during the growth period of winter wheat and summer maize,while the values of root mean square error(RMSE)were less than 0.89 mm/d.As a contrast,the values of R 2 and d in the full irrigation treatment were both higher,and the RMSE was lower than that in other treatments,indicating that water stress affected the estimation accuracy of the model,and the S I model could be better to estimate the crop evapotranspiration under less water stress.