SEBAL Model Improved And Study On The Relationship Between ET And Lucc

With the increasing global water scarcity, evapotranspiration, as one pattern of the main consumption of water, causes more concern. Evapotranspiration includes not only ground and plant surfaces from water evaporation, but also through the plant surfaces and transpiration in plants. Evapotranspiration is an important part in the water cycle, because of water into the gas needed to absorb heat, so heat balance of evaporation and transpiration are the main items. It is of great significance to study Evapotranspiration to understand the context of energy balance and the water cycle.This paper selects typical watershed Luoyugou watershed as study area, TM image on July 31, 1986 and May 19,2006 as raw data, through high-resolution DEM and surface emissivity to improve the SEBAL model. Then the ET (evapotranspiration) is estimated based on the improved model and ground truth data are used to verify the estimated results. Combined with land use maps in corresponding period, distribution of ET is analyzed. The results showed that:①The average inversion result by original model is 3.25mm, the error is 12.68%; the result estimated by improved model is 2.96mm, the average error is 8.32%, the accuracy improved significantly.②Different ET of land use types are significantly different. Basic rule is:water> woodland> Terrace> Construction sites. Among them, water and forest land have the maximum ET, average values were 3.89mm and 3.01mm, terrace, followed by an average of 2.92mm, the minimum is building site, about 2.8mm.③Land use changes significantly in the watershed over the past 20 years, mainly transferring from sloping terraces to the terraces and woodland. Results indicate that land use and cover have extremely significant change, whose total changing area is 87.03%. Terrace lands, natural vegetation and the space of construction increase in varying degrees, increasing by 275.0%,17.05%,14.32%, respectively; Sloping terraces and bare land decrease sharply(decreasing by76.5% and,20.31%, respectively). ET spatial distribution is related to land use/cover characteristics, thereby controlling the ET distribution characteristics in the study area.④Analysis are conducted by daily ET and surface factors. ET and NDVI are linear correlation, the correlation coefficient R2 is 0.58; It is highly linear correlation between ET and vegetation cover, the correlation coefficient R2 is 0.866, ET and surface temperature are exponential relation; It is a weak linear correlation with elevation and relation with slope and aspect is not obvious.⑤In contrast of two ET images, ET significantly increased area accounts for 47.6% of the total area in the valley, however, conspicuously reduced area accounts for 13.2%. In 2006 the ET daily volume in various land-use types is larger than the one in 1986, which was induced by climate change that caused a gradual increase in average temperature in the Loess Plateau, the annual rainfall and runoff on the decrease and dry climate allowing more energy for moisture evaporation. In addition, a large number of man-made engineering and ecological engineering construction causes land-use structure changes that are more conducive to water consumption. Last but not least, two periods'ET shows common features that the largest is body of water, followed by terraced fields, and then construction land. In different land use and cover types, the vegetation coverage and ET exist the apparent correlation.Land surface ET as a response to land use/cover change caused changes in surface water heat-sensitive factors, changes in terrestrial ecosystems is significant to the study of climate feedback effects. It is important that studying the distribution of evapotranspiration can aid policy and decision makers for land use planning and environmental construction in Luoyugou watershed.