Evapotranspiration and energy balance analysis for Tamarix ramosissima stands under extreme arid conditions

Given the increasing threat of water shortages in the extremely arid regions(rainfall 50 mm yr-1) of northwestern China,growing season evapotranspiration(ET) associated with native species such as Tamarix ramosissima is of particular interest.Consequently,this study sought to evaluate the accuracy of daily ET estimates using Bowen ratio data,as well as measuring seasonal ET and development of an energy balance for a stand of T.ramosissima.Bowen ratio apparatus measurements of ET were carried out on a stand of T.ramosissima in a 2.04 km2 field,which are all covered with T.ramosissima near Erdaoqiao,Ejina Province,Inner Mongolia Autonomous Region,China.Soil moisture content and green area index were also monitored.Daily ET could be accurately estimated from Bowen ratio data on a continuous basis over the 153-day growing season.The mean daily T.ramosissima ET over this period was 1.62 mm d-1,for a seasonal total of 248.2mm.In this extremely arid locale,the great majority of available energy dissipated over the growing season was a result of sensible rather than latent heat fluxes.While the heat storage term was the main source of energy at night and a considerable sink of energy during the daytime,the magnitude of the daily mean soil heat flux was small.Such a determination of temporal and ecosystem specific ET patterns allows an improved prediction of ET in the desert riparian zone.