Wet Canopy Evaporation Rate of Three Stands in Western Sichuan, China

The wet canopy evaporation rate (Er) wascalculated by Penman-Monteith combination model based on three assumptions and with meteorological variables 2 m above the canopy inthree stands, dominated by spruce (SF), fir (FF) and birch (BF) trees, respectively[(,)( )]in the subalpineforests in western Sichuan, China over a growingseason. The total amount of the E was 44.5 mm forSF, 88.5 mm for FF and 57.8 mm for BF, accounting for 9.2%, 16.6% and 10.2% of the gross rainfall,respectively, in the measuring period. There was the highest average monthly Er and percentage of E togross rainfall for FF compared with SF and BF.Mean Er was 0.097 mm h-1 (ranging from 0.028 to0.487 mm h-1), 0.242 mm h-1 (from 0.068 to 0.711 mm h-1) and 0.149 mm h-1 (from 0.060 to 0.576 mm h-1for SF, FF and BF, respectively. The highest average monthly Er occurred in June was 0.120 mm h-1 forSF, 0.317 mm h-1 for FF and 0.169 mm h-1 for BF, and the lowest value in October was 0.083 mm h-1 for SF, 0.187 mm h-1 for FF and 0.101 mm h-1 for BF,respectively. The averages of Er from 8:00 to 16:00were significantly higher than those from 0:00 to8:00 and from 16:00 to 0:00 for the three stands. The marked daily and monthly differences of Er were contributable to the variations of solar radiation, air temperature and relative humidity above thecanopy.