| Evapotranspiration is a natural process of water in nature,not only an important component of the ecological circle of water circulation,but also an important component in the energy cycle between the terrain system and the atmosphere.It has great significance to measure and model the evapotranspiration for optimizing regional water allocation,water resource planning and management,as well as assessing the impacts of climate and human activities on ecosystems.In this paper,through the use of closed-path laser analyzer,the observation of field high resolution evapotranspiration for two consecutive years in a vegetable farmland in the suburb of Yueyang city,Hunan province was obtained and the temporal characteristics of evapotranspiration in the study area was studied.Based on the observation and investigation of crop growth and argriculture management practices,the effects of agricultural activities and environmental factors on evapotranspiration were studied by numeric modelling and correlation analysis.The actual evapotranspiration,water vapor flux,latent heat flux(LE)were calculated by using high resolution water vapor concentration data and wind speed data from October 2014 to September 2016 by the software of EddyPro.By analyzing the varioution of the actual evapotranspiration in different time scales,the following temporal characteristics of the evapotranspiration in the vegetation field was obtained :it is higher in the spring and in the summer,while lower in the autumn and in the winter;it is also higher in planting season whilelower in non-planting season;it is higher in sunny daywhile lower in rainy days;it reaches peak in noon while is about to zero at night.The results showed that the evapotranspiration was 730 mm in 2015 and the average daily evapotranspiration was 2.0mm/day.The evapotranspiration in2016 was 803 mm and the average daily evapotranspiration was 2.2mm / day.In addition,the effects of various agricultural practices on the actual evapotranspiration wereinvestigated by using high-resolution measured data.In this study,the evapotranspiration was increased by the practice of planting and was decreased by harvesting,and the decrease by harvesting was significantly higher than that the increase of planting.While irrigation also contributes to the promotion ofevapotranspiration,it is however less pronounced.The effect of fertilization on evapotranspiration is not significant by observation data.RZWQM stands for Root Zone Water Quality Model,with six modules,namely physical modules,chemical modules,nutrient modules,pesticide modules,crop modules and management modules.In this study,according to the meteorological factor data,initial data,soil data and field management data of field observation as the driving variables of RZWQM2 model,the RZWQM2 root water quality model was used to simulate the evapotranspiration and compared with the measured data..The results show that the simulated evapotranspiration R2 and RMSE are 0.79 and 0.013 respectively.The simulated groundwater level,soil residual water,leaf area index and crop height R2 were 0.71,0.77,0.98 and 0.97 respectively.In general,the RZWQM2 model has good simulation results for evapotranspiration and environmental factors.In addition,this paper studied the effects of different agricultural activities on plant transpiration through the model.The most influential factors were crop density,followed by irrigation and fertilizer.Finally,in order to further understand the influencing factors of actual evapotranspiration,we do regression analysis about six meteorological factors for the planting season and non-planting season,the study on the influential factors for evapotranspirationobserved that air temperature has the highest correlation following by soil temperature,solar radiation,soil moisture,rainfall,wind speed and relative humidity.All factors are positively correlated except speed and relative humidity with negative correlations.The correlation between plant height and evapotranspiration showed that these two variables were significantly correlated with confidence at 95%;while the correlation in the first half of the planting season was substantially higher than in the second half of the planting season.To some extent,this is due to the weather factors such as air and soil temperature and solar radiation etc.are rising with the growth of the crops in thefirst half of the planting season;while these factors are decreasing with the growth of crops.This study has the following innovations and findings:1,It is the first use of the closed-path laser analyzer to measured the farmand evaporation in China,which solves the problem to measure the evaporation in rainy days that is the bottleneck for the traditional eddy covariance method.2,In this paper,the effects of different agricultural activities on actual evapotranspiration were investigated using high-resolution measured data.3,The effects of agricultural activities such as crop planting density,irrigation amount and fertilization on the evapotranspiration were studied by RZWQM2 numerical model based on the actual high resolution and long term evapotranspiration data. |
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