Pattern Of The Spatial And Temporal Distribution For Regional Evapotranspiration In Gannan Grassland Based On Modis Data

Based on the increasing pressure on water resources and the situation of grassland degradation of Gannan grassland ecosystems, this research use the more reasonable and accurate Surface Energy Balance System (SEBS) model, which has a solid theoretical basis and has a small restriction of regional application, to estimate land surface evapotranspiration(ET). On this basis, the new generation of earth observation data MODIS is used in the inversion of regional surface ET in Gannan grassland, in addition, the daily ET of Gannan grassland is also inversed in July, with analyzing the temporal and spatial distribution pattern and the changes in developments of regional ET between 2000 and 2009. At the same time, the study uses fractal cross-hatching of image method to describe well the parts of remote sensing ET and microcosmic structure character in the studied area, so as to learn the differences of spatial distribution and change trends of remote sensing ET. According to the results of fractal calculation, the fractal number of cross-hatching in 2000 is 1.237 and 2009 is 1.337. The fractal number of cross-hatching in 2009 is high, profile curve ups and downs, and the grads of ET is big and it has a heterogeneous distribution; fractal number of cross-hatching in 2000 is smaller than that in 2009, profile curve is flat, the grads of ET is small and the distribution is well-proportioned. The essential decisive factors are the patch size of the various landscapes, the number and the combination of space, especially, the degree uniformity of the distribution in landscapes in research area plays a crucial part in the fractal number of ET. The research shows that: as a whole, the average daily ET is in the reduction; in some regions the amplitude of variation is large, and areas which have changed largely are the districts from Bailongjiang to Wubaixiang in Zhouqu county, where the decrease is about 50%. Among them, imudoutang and Sangke grassland scenic pond have rich water in the surface, as well as peaceful deer farm near the West bank of the Yellow River tributaries, Gahai Nature Reserve, Branch bitter river, Bailongjiang, Dam River and Taohe body of water around the water, about the amount of only 7.00mm, and the main reason is the reduction of water resources in the region. Meanwhile, by experimental verification, the differentials between simulation values and observations values is about 0.30mm, the smallest differentials is only 0.07mm, the biggest differentials is only 0.48mm, overall, the simulation results is accurate.