Evapotranspiration Variation In Cascade Ecosystem In Horqin Sandy Land

We used Large Aperture Scintillometer、Eddy Covariance、meteorological systems and vegetation physiological characteristics to discussion and analysis the dynamic characteristic of evapotranspiration and the main driving factors in the different surface in the area, and the area in Horqin sandy was selected as the study area. We introduced footprint function for analyzing the differences of two methods, and it could provide the basis for point scale of the water and heat fluxes transform surface scales. The main conclusions are as follows:(1)The evapotranspiration showed a single peak on sunny day, and the cloudy day was irregular. The evaporation of sunshine was higher than cloudy days’, the greatest difference was 0.4mm around noon.The evapotranspiration of the spring and winter was smaller and the evapotranspiration of the summer and autumn was larger, it had peaked in July. It would have significantly increased and lag about one or two days after the rain.The correlation of the evapotranspiration and the net radiance was also well every month, it was best in June and the R2 was 0.901. The influence of relative humidity、air temperature、wind speed and surface temperature for each month evapotranspiration was basically the same.(2)The daily variational trends of the evapotranspiration were more similar in the different periods throughout the growing season in the sand dunes、farmlands and meadows, and there were multi-peak and broad peak that low in the morning and evening、 higher around the noon and the peak around 14:00. Evapotranspiration had obvious seasonal changes that the spring and autumn was smaller, the summer was larger, the evapotranspiration of farmlands and meadows clearly larger than the sand dunes’. In the growing season, the timings of the peak had differences in different surface, the maximum of sand dunes in June、the maximum of meadows in July、the maximum of farmland in August. In different surface, there were differences that every meteorological factor has an effect on ET. In the sand dunes, the degree of influences of the factors on evapotranspiration was Rn> WS, the evapotranspiration was associated with air temperature and relative humidity was not obvious; In the farmlands, the degree of influences was Rn>Ta>RH, the correlation of wind speed and evapotranspiration was the worst;ln the meadows,the degree of influences was Rn>RH>Ta, evapotranspiration and wind speed has no obvious correlation.(3)Taking datas of July as an example, compared the sensible heat flux data of LAS and EC, in daily changes the results showed a significant consistency. The analysis showed that the EC of the middle of the LAS path correlated significantly with their data. For monthly sensible heat flux and latent heat flux comparison, the date measurements by LAS is larger than the date measurements by EC. But due to different surfaces, the sensible heat flux of field and meadow were difference with the LAS, the latent heat flux of dune were larger difference with the LAS. We conduct computational analysis for the source area of the EC and LAS by the footprint function, the field and meadow’s source area of 80% was only about 1/50 and 1/70 of the LAS’s source area of 80%, it was not representative and limited to the site, so that the data of two systems flux observation were relatively consistent trend, but there were differences in values.