基于SHAW模型对农田小气候要素的模拟

Evaluation of SHAW model in simulating energy balance,leaf temperature and micrometeorological variables within a maize canopy

能量平衡是作物冠层水热传输的基础,气象因子(如空气温度、湿度、风速和土壤温度)是影响作物活动的外界条件,而叶温反映作物的整体健康状况。对冠层状况的理解和模拟有利于了解小气候特征并加强农田管理。采用SHAW(theSimultaneousHeatandWater)模型模拟:冠层表面能量平衡,表面辐射温度,冠层中叶温、气象要素和土壤温度廓线,模型的输入数据来源于华北平原禹城综合试验站。模型很好的模拟了表面能量平衡、冠层表面辐射温度、土壤温度、冠层2/3高度以下叶温和2/3高度以上气象要素。模型模拟净辐射(Rn)的效率达到0.97,潜热(LE)和感热通量(Hs)的模拟效率分别为0.81和0.78,模拟的表面辐射温度与实测值吻合较好,其模拟效率为0.91,冠层2/3高度以下的叶温模拟效率为0.76～0.86,但该高度以上的模拟结果不理想。除了2cm深度外,各层土壤温度模拟较好。

Yucheng is a typical city in the North China plain, which is one of the most important growing districts of grain. Research on it will benefit to the agriculture of the whole region. Furthermore, energy balance is the basis for simulating heat and water transfer in crop canopy. Temperature reflects the condition of plant objectively. Meteorological factors such as air temperature, humidity and wind speed as well as soil temperature are the ambient conditions that affect the activity of plants. Canopy temperature reflects the overall plant health. Understanding and simulating canopy conditions can assist in better acknowledgement of microclimate characteristics and management solutions. The Simultaneous Heat and Water （SHAW） model was used in this study to simulate the surface energy balance, profiles of leaf temperature and micrometeorological variables of a maize canopy and underlying soil temperatures using data collected in Yucheng. The results indicated that the model well simulated air temperature, relative humidity and wind speed in the upper layers rather than the lower, with model efficiency falling from about 0.95 to very small. Since poor simulation occurred especially for wind speed, modification was made to the model, and the simulation was improved accordingly. Energy balance of canopy surface was simulated throughout the growing season of maize using the modified model as above. The simulated net radiation mimicked with the measured, with model efficiency equaling 0.97. The simulations of latent and sensible heat flux were reasonable with model efficiency 0.81 and 0.78 respectively. But the bias of ground heat flux was obvious, which may due to the lack of measured energy balance closure. In addition, the simulation discovered that the precipitation influenced measurement significantly. The coefficient of simulated and measured radiometric temperature reached above 0.9, when the temperature was higher than 30C, the simulated temperature was 0. 34C bigger than the measured. The leaf temperature above the 2/3 of plant height was simulated better than the lower layers with model efficiency equaling 0.85. The soil temperatures near surface were simulated well with model efficiency above 0.80. The simulated temperature was higher than measured value near surface but lower in the deep depth. In conclusion, the SHAW model simulated variables above of maize canopy in typical region of the North China Plain reasonably, and some weakness of the model were discovered, which will be the reference of improvement of the SHAW model and the development of others.