Estimation And Analysis Of Land Surface Water And Heat Fluxes In Mountain-plain Area Based On Remote Sensing And DEM

The income and expenses status of water along with heat on land surface determine the form and evolvement of environment to a great extent. So the matter of water and heat is the core of environmental study, and as at that connecting the energy with evapotranspiration in parallel to study the water and heat effect is the focal point. Thereinto, the accurate estimation of land surface water and heat flux is a complicated problem, which is very important to understanding climate change and hydrological circulation on global or regional scale. Remote sensing and DEM play a more and more important role in monitoring or simulating land surface water and heat transfer process. The introduction of them provides a robust approach on quantitatively study the spatial pattern and process of water along with heat on heterogeneous landscape and complex terrain.This paper focus on the topic of estimation and analysis of land surface water and heat fluxes in mountain-plain area based on remote sensing and DEM, selecting Sunan Mountain and Zhangye Plain as a case study. To achieve the goal that estimating land surface water and heat fluxes (sensible heat flux and latent heat flux) more accurately, a combination of physical-based land surface heat fluxes model and high-quality remote sensing data are needed. First, methodologies and models on parameterization of land surface water and heat fluxes were investigated in details in this paper. Then the high-quality remote sensing data which mostly fulfilled by ASTER was selected and processed by geometric correction to match with DEM, calibration and atmospheric correction to convert to surface reflectance. Biophysical parameters, such as albedo, vegetation fraction, leaf area index (LAI), canopy height, land surface temperature etc., were retrieved quantitatively from ASTER after analyzing many algorithms and selecting the feasible ones. On simulating solar radiation, topographic factors, such as slope and aspect, were considered, which make it possible for the precise estimation of incoming shortwave radiation in mountainous area. All the parameters were as the input of SVAT-based model—SEBS, who has some improvements on parameterization of the important sensible heat flux, to derive the latent heat flux and daily evaporation. In succession, to clarify particularly on two landform systems—mountain and plain, the spatial pattern of land surface heat fluxes as well as daily evaporation were corss-compared, exploring the influences of land surface heterogeneity and terrain complexity on them.Based on the upper methods the following conclusions were made:After preliminary validation and comparison, we consider that the estimation of land surface water and heat fluxes as well as daily evaporation shows a reliable result, which also implies that the parameterization methods and SEBS model are feasible;Doing correlation analyses between latent heat flux (daily evaporation) and land surface heterogeneity such as land use land cover (LULC), NDVI, vegetation fraction and LAI, the results show that land surface heterogeneity has great influence on the spatial pattern of land surface water and heat fluxes, and vegetation coverage influence surface water and heat' s characteristic. Different types of LULC have their corresponding threshold concentrations, and the high vegetation density corresponds to high evaporation. Forest, prairie and grassland, irrigated field have higher daily evaporation, while cold desert, Gobi and droughty riverside land have low daily evaporation, some of which reach to 0. Land surface temperature (Ts) also has influence on their spatial distribution. Comparing the above-mentioned parameters' simulative correlation with latent heat flux and daily evaporation, we deem that it is better to introduce vegetation fraction and Ts to describe land surface water and heat fluxes rather than the commonly used NDVI-Ts, though it needs further analysis and validation;Comparing Sunan Mountain to Zhangye Plain, we find that the distribution of land surface heat fluxes at Sunan Mountain is very complex. It is not only impacted by vegetation condition, but also relates to the topographical factor, such as aspect, slope and elevation, by conducting correlation analysis. Besides the vegetation coverage, terrain complexity dominates the spatial distribution of land surface heat fluxes in mountainous area, which are distinctly different from plain in quantity and spatial law. Furthermore, the standard deviation error caused by not taking terrain complexity into account is calculated. The results show that the standard deviation of the net radiation flux error and latent heat flux error are almost linearly with the standard deviation of height. In certain range, they have significant correlativity with the standard deviation of slope and aspect. These correlations with net radiation flux are even more obviously. The results also demonstrate that it is necessary to consider terrain complexity when estimation of land surface energy and mass fluxes in mountainous areas.