Analysis of effects of climate change on evapotranspiration in Zhalong wetland in recent 40 years

By using the meteorological data from 1961 to 2000, the change trends of four meteorological factors, the maximum temperature (θmax), the minimum temperature (θmin), wind speed at 2 meters (U2) and precipitation (P) were detected, and the effects of climate change on evapotranspiration (.E) from reed swamp of Zhalong wetland were analyzed. The trend analyses are performed by univariate Mann-Kendall test, a well-performed experiential model is introduced for E calculating. The results show that significant increasing trend is found of θmin in recent 40 years in Zhalong wetland region, the climatic tendency is 0.74°C/10 a, however, no significant increasing trend is found of θmax, the climatic tendency is 0.15°C/10 a, the U2 shows significant degressive trend, and no evident change of P in the region studied is detected, the annual E on reed swamp shows degressive tendency, the decrease in recent 40 years is 92 mm. The trend analysis and sensitivity analysis of meteorological factors illuminate that θmax and θmin are two key factors which influence E markedly, the difference of the change speed between them results in the decrease of E, the records of θmax and θmin mean the augment of greenhouse gas and aerosol in the atmosphere, these substances serve as a screen to prevent the heat transferring to outer space and at the same time reduce extraterrestrial radiation, consequently, decrease net radiation, the most correlative variable to E.