Wet canopy evaporation rate of three stands in Western Sichuan, China

Abstract

The wet canopy evaporation rate (Er) was calculated by Penman-Monteith combination model based on three assumptions and with meteorological variables 2 m above the canopy in three stands, dominated by spruce (SF), fir (FF) and birch (BF) trees, respectively, in the subalpine forests in western Sichuan, China over a growing season. The total amount of theE was 44.5 mm for SF, 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 monthlyEr and percentage ofE to gross rainfall for FF compared with SF and BF. MeanEr was 0.097 mm h−1 (ranging from 0.028 to 0.487 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−1) for SF, FF and BF, respectively. The highest average monthlyEr occurred in June was 0.120 mm h−1 for SF, 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 ofEr from 8:00 to 16:00 were significantly higher than those from 0:00 to 8:00 and from 16:00 to 0:00 for the three stands. The marked daily and monthly differences ofEr were contributable to the variations of solar radiation, air temperature and relative humidity above the canopy.