Measurement of evapotranspiration of mixed bush and grass in headwater region of North China Plain

摘要

Bowen ratio and energy balance (BREB) method is used to measure the evapotranspiration of mixed bush and grass in headwater region of North China Plain. The results show that it is hard to observe the long-term data by BREB. To analyze the diurnal variation in the energy balance, three days (DOY 225, clear day; DOY 228, cloudy, fog in the morning, and 0.2mm of precipitation; DOY 236, cloudy) in 2001 are selected from the growing period of vegetation. Actual evapotranspiration is -4.13, 0.95, and 3.38 mm/day, with mean value of 2.82 mm/day. Peak hourly ET is 0.66 mm/hour. Bowen ratio is 0.28, 0.30, and 0.35 on DOY 225, 228, and 236, respectively. The daily ET0 calculated by hourly Penmen-Monteith mothod on DOY 225, 228, and 236 is 4.68, 1.04, and 3.54 mm/day. Crop coefficient (Kc) is 0.88, 0.92, and 0.96, respectively. The variation of Kc is in agreement with the ET in clear day.