Characteristics and Law Analysis of Energy Flux in Southern Water-saving Irrigation Paddy Field

Liu Xiaoyin;Yang Shihong;Li Jiwen;Xu Junzeng;Liu Ming;State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering,Hohai University;College of Water Conservancy and Hydropower Engineering,Hohai Univerbity;

Water-saving irrigation paddy field Energy flux Eddy covariance method Energy;;balance

Based on the observation data,including net radiation flux,latent heat flux,sensible heat flux,soil heat flux,etc.,which were surveyed at the stage of rice growth in 2013 at Kunshan Irrigation and Drainage Experiment Station with eddy covariance method,this article analyzes the features and distribution characteristics of energy balance components in the typical sunny day and cloudy day,as well as the diurnal and monthly variations of energy fluxes in rice season. The ratios of energy balance components to the net radiation and the energy closure degree of paddy field in different temporal scales were also discussed. The results illustrated that the monthly averaged diurnal variations of energy balance components,which were observed in typical sunny day in southern subtropical monsoon region at the stage of rice growth,obviously presented as the singlet trend of inverted "U"shape. The daily mean value and peak value of energy balance components in typical sunny day were smaller than that in cloudy day,but it also presented as the trend of singlet variation. The difference between latent heat flux and sensible heat flux appeared apparently. The ratios of the above two to the net radiation were anticonnected and the values were 86. 2% and 0. 8%,respectively. The ratio of the soil heat flux to the netradiation was 1. 3%. As a result,the latent heat flux was the main component of net radiation in different temporal scales. Due to out-sync of energy transformation, turbulent fluxes lagged behind the net radiation about 0. 5 h,and the hysteresis of surface soil heat flux was about 1. 5 ~ 2. 5 h. Energy balance components in different time spots were corresponding incompletely as to the impact to the short-term energy closure rate. But compared with other ecosystems,there was a better energy balance closure in water-saving irrigation paddy field,which suggested the flux data measured by eddy covariance method was capable to act as an effective judgment for evaluating the availability of energy flux features.