Evapotranspiration (ET) of major aquatic plants in wetland is usually needed to be evaluated in water resources management to provide optimum water for wetland. Reed swamp is a typical underlying type of Zhalong wetland, and is also the critical living condition for aquatic birds, such as crane and swan. In order to study the rules of ET change in wetland, and make scientific prediction for ET water requirement during different periods, a study was performed to investigate the trend of climatic factors in Zhalong wetland. The ET for the period of one hundred years (1961 to 2060) was estimated and predicted. In addition, the effect of climate change on wetland was analyzed.
An empirical model which coupled the maximum temperature (Tmax), the minimum temperature (Tmin), wind speed at 2 meter (U2), and precipitation (P), was used for ET calculation and sensitivity analysis for meteorological variables. The univariate Mann-Kendall (M-K) test was conducted to investigate the trend of meteorological variables on different research sites. During the period of 1961～2000, the meteorological data set at five weather stations around Zhalong wetland was used for ET estimation. During the period of 2001～2060, the climatic scenarios of four General Circulation models (GCMs), HadCM3, CCSRNIES, CSIRO-Mk2 and CGCM1, were utilized to predict future ET.
The M-K test of meteorological variables showed that the predicted data from GCMs could reflect the actual change trend for the study area, and the test results were reasonable. The results showed that the mean ET for the periods of 2001～2020, 2021～2040, and 2041～2060, is larger than the mean value in the past forty years. The Tmax and the T_min were proved to be two dominating factors which influence ET significantly, and the difference in the increase rate between T_max and T_min determined the change trend of ET. The results also showed that the wind speed will decrease about 0.28 percent, and precipitation will increase about 4.7 percent. The influence of wind speed and precipitation on ET will be less than one percent, which is not significant compared to T_max and T_min. Based on the results of GCMs prediction scenarios, the increase of T_max (1.1～3.5℃) and T_min (1.2～3.9℃) will result in additional water consumption of 15%～22% for reed swamp. In the future, the water requirement of ET in wetland will increase evidently, since the wetland surface will become dryer without significant precipitation increment, which could lead to the increase of the ecological water demand in the wetland region.