Characteristics Of Water Vapor Flux And Evapotranspiration Of Urban Lawn

With the area of urban lawn increasing, the lawn ET has become one of the water balance important factor on maintaining the global ecosystem, long-term observations, statistics and analysis the water vapor flux of the turf in large-scale range play an important role on urbanization and global climate change. The test by the eddy covariance method and lysimeter method, comparative studies water vapor flux, photosynthetic indicators of plants in two scales and under different irrigation, and correlation analysis combinated with meteorological factors. The results showed that:(1) Water vapor flux and heat flux trends are inverted "U" shape, during the day is positive, night is negative, which is contrary to the CO2flux curve; except for March, other water vapor flux curve and the latent heat flux is almost coincident, and both curves is far higher than the sensible heat flux; hours throughout the day transpiration is reduced with the shorter sunshine hours, the basic performance is the summer maximum, spring and autumn, winter minimum; annual intermediate periods Bowen ratioβ smaller, winter and spring larger; the combined effect of the CO2flux and vapor flux causes WUE day dynamic curve up and down, the change is more complex.(2) Moisture conditions can significantly affect grass ET. ET follow "the greater the soil moisture, the ET is greater" the law, the same period sunny than cloudy. The grass ET of restricted irrigation in August was bimodal, other bluegrass ET showed a single peak and the peak before the day the maximum temperature value; ET reduces with the solar radiation and temperature smaller monthly; The grass ET between11:00～15:00takes a large proportion of the day, about47%; the grass growth rate and all of the above ground biomass accumulation from big to small:F5> F4> F3> F2> F1; the changes of grass net photosynthetic rate, transpiration rate and stomatal conductance each month are generally consistent with U-type.(3) The influence of the same kind of meteorological factors on different plant water vapor flux, photosynthetic indexes is not equal, and the response of water vapor flux, photosynthetic indexes in the same month to different meteorological factors are not the same. The response of water vapor flux, photosynthetic indexes to solar radiation, temperature is most significant, followed by wind speed; they has shown a highly significant negative correlation with air relative humidity, wind direction followed.(4) The ET0in March to November changes with solar radiation, temperature and other meteorological factors reduced monthly; the crop coefficient measured by lysimeter method is larger than the eddy covariance method, under the same conditions, the greater the soil moisture content, the larger the Ks. The water flux using the eddy covariance method can calculate all of the experimental lawn grass evapotranspiration about560.6mm from March to November.