以气象观测资料为基础,采用波文比能量平衡法(BREB)对低湿草地的蒸散进行了估算。结果表明,在一个完整年度内,试验地蒸散量(ET)为611.5mm,日均1.67mm。在牧草不同生长季节,ET变化剧烈,非生长期、生长初期、生长中期、生长末期分别为0.57mm/d、2.01mm/d、3.82mm/d和1.49mm/d,蒸散量分别占全年蒸散总量的18.26%、9.20%、61.83%和10.71%。ET月变化显示,从3月开始草地蒸散量有所增大,6月牧草进入生长中期后蒸散量迅速增大,到7月蒸散量达到最大,9月牧草进入生长末期,蒸散急剧减小;随着牧草生长终结和土壤冻结,蒸散量逐步减小,在11月中旬到次年2月蒸散基本停止。蒸散的日内变化规律显示,草地蒸散开始于早晨7:00～8:00,13:00左右达到最大,19:00～20:00蒸散趋于0。晴天蒸散强度远大于阴天。 更多还原
 

Low-lying wet-grasslands characterized both as grasslands and wetlands possess irreplaceable ecological functions in the inner river basins of Northwest China.Bowen-Ratio Energy Balance(BREB)method was used to calculate evapotranspiration(ET)based on meteorological data from low-lying wet-grassland in the middle reach of the Heihe River basin in Hexi Corridor.Results reveal that ET rate for the period 2003 to 2004 for the wet-grassland is 611.5mm/a and 1.67mm/d.ET varies with different growth stages,with 0.57mm/d in No Growth Stage(NGS),2.01mm/d in Initial Growth Stage(IGS),3.82mm/d in Middle Growth Stage(MGS) and 1.49mm/d in End Growth Stage(EGS).ET for the four growth stages mentioned above respectively accounts for 18.26%,9.20%,61.83% and 10.71% of the total annual ET.In March,ET begins to increase,and with the growth of grass in June,it increases sharply,reaching its maximum in July.After July,ET decreases gradually.In Sept.,ET decreases rapidly and stops at EGS in mid Nov.,which happens at the freezing of the soil until Feb.of the following year.Hourly ET analysis shows that evapotranspiration begins at 7:00(for MGS) or 8:00(for EGS),and rises to a maximum value at 13:00,then finally ends at 19:00(for EGS) or 20:00(for MGS).ET intensity on sunny days is always much higher than that on cloudy days for the same growth stage.