Estimation Of Evapotranspiration In Mountainous City

The variation of regional land surface Evapotranspiration (ET) reflects the trendof energy and water balance in land surface process. Also it further affects distributionof the regional climate and water, and thus has an impact on regional economicdevelopment. With the development of remote sensing technology, it becomes moreeasily to explore the land surface ET of large scale. Therefore, it is a promising themeto carry out a research related to monitoring land surface energy and water balance onregional scale based on the remote sensing technique.In this paper, as one of the main means of remote sensing technology, consideringaltitude, aspect, slope and other factors surrounding terrain masking, improved landsurface energy balance model to improve the estimation accuracy of the model, sothat the model can adapt to complex terrain conditional areas under surfaceevapotranspiration estimates, expanding the usage scope of evapotranspiration model.The thesis regards the Chongqing as a case, and also analyses and explores thetemporal and spatial distribution of land surface ET on June11, July30, August7in2013, which has more important theoretical and practical value. Specific researchwork and conclusions of this paper are as follows.(1)There has a good relationship between surface temperature and altitude in theregion above1000meters, and the fit goodness reached0.75.Therefore, the surfacetemperatures of1,000meters above the terrain area have been corrected. Aftercorrection surface temperature high values mainly distribute in main city andsurrounding counties, and there have the characteristics of lower vegetation coverage,building more intensive and human activities affect relatively strong. Low valuesmainly distributed in Northeast and Southeast of Chongqing, and there being a goodecological environment, the vegetation coverage rate is relatively high, and relativelyweak impact of human activities. (2) Improvement of estimation for the global solar radiation in rugged terrainbased on DEM, and applied it to the estimation of complex terrain area net radiationflux. The results show that: the spatial distribution of net radiation flux in Chongqinghas obvious regularity, high-value areas are located in Qijiang-nanchuan-Fuling-Fengdu-pillars-Wanzhou-Fengjie and other areas on the mountains, those areas athigher elevations, and vegetation coverage higher and lower albedo, absorption ofsolar radiation intensity; low value areas are located in Wuxi-Wulong-pengshui-Qianjiang-YANG-Xiushan other regions. Although the vegetation cover in thesereas relatively better, and albedo is not higher, but the sun’s radiation is less in theseregions because impact by clouds, the amount of nte radiation received will bedecreased in surface. Surface net radiation flux in the study area also has an obvioustopographical distribution, the main features as following: net radiation values inridge are greater than the valley of the; sunny net radiation values higher than shady.With sea level rise, net radiation has a gradually increasing trend with increase ofaltitude, but the increasing amplitude is opposite.(3) Estimation of evapotranspiration and based on the usage of improved balancealgorithm for land surface energy in the study area.and use of the ratio method andsine law extend the time-scale from the instantaneous evapotranspiration to the dateevapotranspiration, and use the method attest the model recommended by FAO-PM.The results show that the accuracy of estimated evapotranspiration is relatively higherwhen utilized improved land surface energy balance model surface, and the model hasa relatively good stability and adaptability in the study area. The average relative errorof daily evapotranspiration ratio method is18.76%; average relative error of sine lawdaily evapotranspiration is9.05%, except for a few points relative error is too large,the relative error of the two methods are within tolerance limits. However，relatively，daily evapotranspiration estimation based on the sine law has higher precision thanET results.(4) There are some differences in spatial distribution of evapotranspiration, andevapotranspiration under different land covers are also different. Generally, the spatialdistribution of evapotranspiration evapotranspiration in the Southeast and Northeastof Chongqing higher than Yuxi region, high value areas are also acattered located inQijiang, nanchuan and other Yuxi regions. Daily evapotranspiration for different landcover types have some differences, daily evapotranspiration descending order: water,grassland, woodland, farmland, unused land, and artificial surfaces. (5) The distribution of evapotranspiration influence by many factors, the paperselected two-factor are surface temperature and terrain to analyze its effects.evapotranspiration and surface temperature has a significant quadratic function byfitted regression analysis，the correlation coefficient R is0.85. Evapotranspirationincreased with surface temperature when the surface temperature is less than305degrees; Evapotranspiration showed a decreasing trend with the increase of surfacetemperature when the surface temperature is greater than305degrees. Throughanalysis of the relationship between elevation and evapotranspiration, we canconcluded that when the elevation less than2500m, the evapotranspiration graduallyincrease with increased elevation; Evapotranspiration was drastically reduced whenelevation greater than2500m,. The conclusions can be obtained，the slope between0-20degrees, evapotranspiration increases with slope; slope greater than20degreesafter evapotranspiration show a downward trend， when research of the relationshipbetween the slope and evapotranspiration. Generally, average evapotranspiration isrelatively larger in the wester direction than easter direction from the relationshipgraph for evapotranspiration with slope variation.