Estimation Of Actual Evapotranspiration From Rice Field Using Dual Source Model

Evapotranspiration (ET) is the important component of the terrestrial hydrological cycle. It is also a complicated and crucial process controlling the energy and water exchange among soil-plant-atmosphere continuum. It has two parts, soil evaporation and plant transpiration. Water is the most important factor witch restrict the rice production in south of china. As we know, the consumption of agricultural water resources in this area is primarily of field evapotranspiration. It is necessary to developing high-efficient and water-saving agriculture and implementing accurate determination of irrigation water supply and irrigation time. Therefore, the more accurate measurement and assessment of field evapotraspiration is especially indispensable.Based on the paddy field test data, soil evaporation surface resistance between rice plants and the estimating model of canopy resistance for paddy field has been built. Combinating the above model, a dual source evapotranspiration model which is suitable for the climate conditions of paddy field has been applied. Based on the Eddy covariance measurements during 2006 entire late rice growing season, the performance of hourly and daily evapotranspiration (ET) was estimated by both the doul-resource model and the Penman-Monteith model. Respectively, the sensitivity analysis about the five resistances has also been studied.(1) The diurnal change of stomatal resistance are same in different growing stages. The variation in the whole growing season exhibits a relationship of same curve. The stomatal resistance is small between the 9:00-15:00, but then it increases sharply after 15:00. Base on field experimental data, the minimum canopy resistances of japonica and hsien rice have been determined. The estimating model of canopy resistance for paddy field has been made using Jarvis model. It is shown by the analysis and the verification that this model is reasonable. (2) The dual source evapotranspiration model which is suitable for the climate conditions of paddy field has been determined. The linear correlation coefficient of dual source model is higher than PM model's, and the RMSE of dual source model is lower.(3) Respectively, the sensitivity analysis showed the dual source model wasmost sensitive tor_s~c, thenr_s~s, relatively large sensitive to r_a~a and r_a~s, and not sensitiveto r_a~c. It is much important to determine those resistance parameters when usingempirical resistance formula.