Estimation of Evapotranspiration in the Desert–Oasis Transition Zone Using the Water Balance Method and Groundwater Level Fluctuation Method—Taking the Haloxylon ammodendron Forest at the Edge of the Gurbantunggut Desert as an Example

Shallow groundwater is an important water source for Haloxylon ammodendron (H. ammodendron). The accurate estimation of evapotranspiration (ETg) from great significance the cycle and maintenance ecological stability. Using a combination balance method level fluctuation (WTF), components (precipitation, soil moisture, depth, Bowen ratio meteorological data) in desert–oasis transition zone were continuously monitored 2015 to 2018 ETg was estimated results showed that closed degree specific energy after data screening higher, annual actual (ETa) value could be reliably calculated at 260.87 mm. As main contributor consumption growing season, latent heat accounted 70.16~91.86% balance. Precipitation had no significant impact on H. vegetation growth, precipitation season 59.44% ETa. depth study area decreased yearly growth vegetation. Although greater than 9 m, ETg, as part balance, found participate process brought about by due strong root system supporting capillary soil. ETa 244.32 mm, contribution rate high 74.78% or approximately 182.35 After verified using WTF, R 0.96, RMSE range 1.5931~4.5706, bias −0.15~0.11, IOA 0.95. accuracy model high, relatively accurate. can applied obtain estimations provide theoretical guidance scientific basis local resource management protection.