Measurement and estimation of the summertime daily evapotranspiration on alpine meadow in the Qilian Mountains, northwest China

Research on mountain evapotranspiration (ET) is important to help understand water cycling and predict streamflow in cold regions in China. Actual daily ET was measured in two types of micro-lysimeters with depth 40 cm and diameter 31.5 cm (A) and depth 27 cm and diameter 27 cm (B), from 1 July 2007 to 10 September 2007, on an alpine meadow in the Qilian Mountains in northwest China, where Bowen ratio measuring instrument and eddy covariance system are too costly and difficult to be built in the region. The results of micro-lysimeters were used as a way to calibrate and test a number of energy balance methods and determine the pan coefficient (K (p)) for a mountainous site. The results indicate that the FAO-56 Penman-Monteith offers the best performance, with RMSE of 0.61 mm day(-1), MAD of 0.46 mm day(-1), and the index of agreement near 1, followed by ASCE Penman-Monteith, Priestley-Taylor and Hargreaves-Samani, and the K (p) is estimated as 0.7 for the summertime.