Priestley-Taylor Model-based Evapotranspiration In Artemisia Ordosica Ecosystem

Evapotranspiration is an important component of the global hydrological cycle and energy budget,and its response to climate change plays an important role in regional precipitation and dry-wet changes.The Priestley-Taylor(P-T)model is widely used in estimating evapotranspiration because of simple parameters required.The core method here was to determine the a parameter in the PT model using eddy covariance measurements of water and energy flux from 2014-2016 in Artemisia ordosica in the south edge of Mu Us desert,and then estimate the evapotranspiration using optimized a value in this region.(1)There were obvious seasonal changes in the actual a coefficient in the period of 2014-2016.During the leafing period,the a coefficient showed a unimodal change trend and the daily mean maximum occurred in leaf extension period.The a coefficient in the expanded leaf period was relatively stable and showed a increasing trend.The a coefficient in the period of leaf color change period showed a decreasing trend.(2)Saturated vapor pressure deficit(VPD),soil water content at 30 cm depth(SWC30),canopy conductance(gs),and leaf area index(LAI)all have a certain regulation effect on αcoefficient.During the observation period,the canopy conductance(gs)and the saturated vapor pressure deficit(VPD)had obvious threshold on the control of the a coefficient.When gs was less than the threshold(3.5±0.5 mm/s),the a coefficient increased with increasing gs.When it was greater than the threshold,the changing trend of the a coefficient was not obvious.When VPD was less than the threshold(2±0.5)kPa,the a coefficient increased with increasing VPD,and when VPD was greater than the threshold,the a coefficient was almost unchanged.Soil water content(30 cm)and leaf area index and a coefficient showed a positive correlation.(3)The evapotranspiration(ETi.26)estimated by the conventional coefficient a=1.26 of the P-T model and that estimated by the P-T model coefficient a=0.50 from the daily temperature and the wind speed data at the height of 2 m(ET0.50)were significantly larger than the measured ones.The localization of the improved P-T model coefficients here was recommended to be 0.23,and the corresponding estimates of ET had a good agreement with the measured ones.In conclusion,the modified P-T model significantly improves the estimation accuracy of evapotranspiration in semi-arid region,heping with accurately quantifying hydrological process and providing a reliable scientific basis for the scientific management of ecosystems in the region.