Estimation Of Vineyard Evapotranspiration Based On Bowen Ratio In Semi-humid Regions

Grape is a characteristic economic fruit which is developing vigorously in guanzhong area of shaanxi province.However,guanzhong region is located in the semi-arid and semi-humid region of China,which has a shortage of water resources and uneven spatial and temporal distribution of precipitation.The rainfall is mainly concentrated in summer and less in spring,which has caused serious obstacles to the healthy operation of the ecosystem and the improvement of grape yield and quality during the growth period.Therefore,it is of great significance to accurately master the soil water condition and water demand of the grape garden,so as to determine a reasonable irrigation system,provide a theoretical basis for the water management of the vineyard in the semi-humid area,and to maintain a good growing environment for grapes and improve the yield and quality of grapes.This study was carried out on April 1,2018,solstice,August 23,2018,in jundu weier grape manor,yangling district,xianyang city,shaanxi province.Based on the BREB method,this study explored the method of evapotranspiration measurement and simulation applicable to vineyards in sub-humid areas of China,and the following main results were obtained:?1?According to the directional constraints between different components in the hydrothermal balance and the accuracy of the temperature and humidity sensor in the bowen ratio measurement system,the selection range of the data collected by bowen ratio is determined and the data is screened.Taking the evapotranspiration results of water balance method as a reference and comparing the estimation results of bowen ratio and energy balance method,it is found that the bowen ratio method can better reflect the change law of evapotranspiration of vineyards,and the monitoring results are of high accuracy.?2?The distribution characteristics of the water heat flux under different growth stages and under typical weather conditions and the response of the latent heat flux to the relevant meteorological factors were analyzed.The diurnal variation of the water heat flux is shown as the unimodal conic,which increases from around 7:00 am and decreases after reaching the peak at around 12:30 PM,and remains basically unchanged at night.The sensible heat flux accounted for most of the surface energy in the whole growth period,and the latent heat flux was small.The proportion of the latent heat flux gradually increased with the growth period,and began to decrease after the fruit growth period reached its maximum.In rainy days,each component of the hydrothermal balance is smaller than that in sunny days,and the latent heat flux is slightly larger than the sensible heat flux.The diurnal fluctuation of latent heat flux in cloudy days is obviously greater than that in other weather conditions.The latent heat flux simulated by BP neural network based on meteorological factors has a high correlation with the calculated value of bowen ratio method.Meanwhile,the change of latent heat flux is the most sensitive to the change of net radiation and soil heat flux,while the sensitivity to the change of wind speed u is relatively low.?3?To explore the rule of the growth period of grape transpiration evaporation,and then adopt the method of single crop coefficient?K_c?,dual crop coefficient method(K_cb)estimate semi-arid sub-humid regions grape ET,compare the bowen ratio-energy balance method analysis of single and double crop coefficient in sub-humid climate area,the applicability of the vineyard.The change of evapotranspiration of grape in the whole growth period is characterized by obvious seasonal changes.The average daily evapotranspiration is 1.32mm/d and 1.25 mm/d respectively in the germination period and the new shoot growth period.The average daily evapotranspiration of grape in flowering period was 1.22 mm/d.The total cumulative evapotranspiration was 91.56 mm/d after fruit growth.During the period of colouring and ripening,the average daily evapotranspiration of grapes increased continuously with the increasing temperature,and the average daily evapotranspiration reached 2.34 mm/d.The basic crop coefficient of grapes,K_cb,was at a low level at the early stage of growth,with an average value of 0.13.At the middle stage of growth,it increased significantly and remained at a relatively high level.K_cbini,at 0.34,gradually decreased to0.32 at the later stage.On the whole,the soil evaporation coefficient K_e was relatively large at the early stage of development,with the mean value of 0.72 at the initial stage,the minimum value of 0.34 at the middle stage and 0.39 at the later stage.The actual evapotranspiration of grapes calculated by the single and double crop coefficient method is in good agreement with the measurement results of bowen ratio energy balance method,and the estimation results of the double crop coefficient method are more reliable than the single crop coefficient method.Therefore,the double crop coefficient method can provide a more accurate reference for the water demand of grape crops in this region.?4?In this paper,the evapotranspiration of grapes in sub-humid regions was simulated by P-M model and S-W model,and the values of the estimated values and the measured values were compared by the bowen ratio-energy balance method,and the applicability of P-M model and S-W model in the estimation of evapotranspiration of grapes in sub-humid regions of China was analyzed.The average value of evapotranspiration in the whole growth period was 1.69 mm/d,and the simulated mean value of P-M model was 2.65 mm/d.The evapotranspiration in the vineyard in 2018 was overestimated to some extent.The determination coefficient R² of the two was 0.68,the average absolute error MAE was 0.63,and the root mean square error was 0.53 mm/d.The estimated mean value of S-W model is1.79,R² is 0.73,MAE is 0.51,and the root-mean-square error is 0.61 mm/d.On the whole,the S-W model has a better estimation effect and a relatively small deviation,but it overestimates the evapotranspiration of grapes during the growth period.