Simulating evapotranspiration of Qinghai spruce (Picea crassifolia) forest in the Qilian Mountains, northwestern China

Qinghai spruce (Picea crassifolia) forests play an important role in regulating the regional water balance of the Qilian Mountains in northwestern China. The objective of this study was to estimate evapotranspiration (ET) of the Qinghai spruce forest in the middle section of the Qilian Mountains. A modified Penman–Monteith equation was used to simulate two sub-components of ET: canopy transpiration (Et) and soil evaporation (Es). The third sub-component of ET, canopy interception evaporation (Ei), was directly measured. The results show that the total ET of the Qinghai spruce forest was 313.6 mm during the 2008 growing season (from May 1 to September 30). Ei, Et, and Es were 100.9 mm, 160.8 mm and 51.9 mm, and accounted for 32.2%, 51.3% and 16.5% of the total ET, respectively. The total modeled ET during the 2008 growing season is acceptably consistent with the directly measured ET (298.2 mm) by eddy covariance system. The consistency implies that the modified Penman–Monteith equation is an effective method to estimate ET using conventional meteorological data with additional measurements of net radiation, and the method can thus be applied to similar situations where reliable direct measurements are not practical.

► This study estimated ET of Qinghai spruce forest in the middle section of the Qilian Mountains using a modified Penman–Monteith equation. ► The modeled ET for the 2008 growing season is 313.6 mm, being consistent with the measured ET (298.2 mm) by eddy covariance. ► This implies that the modified Penman–Monteith equation is an effective method to estimate ET using conventional meteorological data with additional measurements of net radiation and it can thus be applied to similar situations where direct measurements are not practical.