2.3 Meteorological data collection
All meteorological variables needed to calculate ET0
using the various models were obtained or estimated from the weather
station at Haibei Station, and included relative humidity (RH), wind
speed (WS), net radiation (Rn), total radiation
(Rs), extraterrestrial solar radiation
(Ra), soil heat flux (G), maximum air temperature
(Tmax), vapor pressure deficit (VPD), minimum air
temperature (Tmin) and mean air temperature (T). The
radiation were measured by four radiometers (CNR4, Kipp&Zonen,
Netherlands) at 1.5 m height; relative humidity, wind speed and mean air
temperature were measured at 1.5 m height (HMP45C, Vaisala, Finland),
and wind speed was converted to 2 m height for calculating
ET0. The soil heat flux (G) was measured by three heat
flux plates (HFT-3, Campbell, USA), which were separately buried 5 cm
beneath the surface. Half-hourly means of meteorological data were
stored by a data logger (9210 XLITE, Sutron, USA).