Diurnal Variation Of Evapotranspiration Of Populus Euphratica And Its Relationship With Environmental Factors In Extremely Arid Area

Studying the variation law of regional evapotranspiration is helpful for understanding the water balance of desert riparian forest in extreme arid areas and determining the actual ecological water demand,which is of great significance for the rational utilization of water resources,maintaining the balance and stability of desert riparian forest ecosystem and the ecological hydrological process in arid areas.The actual evapotranspiration(ET)of Populus euphratica was analyzed based on the measured data of eddy-covariance method in Ejin Oasis,Inner Mongolia Autonomous Region.The changes of ET day and phenological period of P.euphratica and the influence of various environmental factors on ET were discussed,in order to further grasp the law of ET of P.euphratica,to ensure the matching of supply and demand of ecological water transfer of P.euphratica in the lower reaches of the Heihe River,provide scientific basis for rational development and utilization of water resources in arid areas,and predict environmental changes in the future.The main conclusions of this paper are as follows:(1)On the whole,the daily ET of P.euphratica shows a wave-like trend of increasing first and then decreasing,with a daily variation range of 2?8 mm and a daily average value of 5 mm.In general,the ET of P.euphratica increased first and then decreased during the growing season and the total ET in 2016 growth season is 794 mm,cumulative ET in fruit period and seed spreading period is the main part of total ET in growth season.(2)Air temperature plays a decisive role in the ET of P.euphratica forests,and its variation law is basically the same as that of ET,and its daily variation has the same peak pattern.(3)The influence degree of environmental factors on ET is as follows:air temperature(0.497)>net radiation(0.472)>soil heat flux(0.270)>wind speed(-0.071)>relative humidity(-0.357).The environmental factors are fitted by multiple stepwise regression,and the equation obtained as follows:ET=1.644+0.116 Ta+0.004 Rn-0.023RH-0.025 G.