Regional Land Surface Water/Heat Flux Modeling And Application Based On Remote Sensing In Shandong Province

Regional land surface water/heat flux monitoring and modeling based on remote sensing is the forefront and hot issues in water resources applications at present. Remote sensing provides an approach to monitor land surface energy and water balance on regional scale simultaneously,which is very important and useful in researches and applications in global climate change,hydrology,ecology,agriculture, etc.A lot of important researches have been done over the past few decades,but due to the temporal and spatial complexity of the land surface water/heat process,there still have many issues to be explored.Therefore,it is a promising scientific theme, both theoretically and practically,to model and monitor land water/heat flux using the regional advantage of remote sensing technology.Taking account of both specific application requirements and model practicability,what spatial scale should,and can, be chosen for regional water/heat flux modeling? As a view to this question,the thesis is to propose a remote sensing model of water/heat flux for land by doing some research,which including spatial heterogeneity analysis,remote sensing data validation and improvement,and discussing the spatial and temporal scale problems. Specific research work and conclusions of this paper are as follows:1)The impact of the spatial heterogeneity for the surface water/heat flux modeling based on remote sensing is firstly analyzed,suggesting that it is necessary to weighed against the complexity of the process and the remote sensing capability to choose a suitable remote sensing scale.Then,the Index of Agreement suggested by Willmott is adopted for successive pixel scales to detect the critical scale of study area,which exhibits a spatial scale of 250～500 m that agrees with analysis result of land cover texture,land cover pixel and spatial semivariance.2)Digital elevation model(DEM)is successfully coupled in the SEBAL model for the topography correction(slope,aspect and elevation),expanding the application of the regional ET remote sensing model.On the basis of the lookup-table of land surface dynamic parameters suggested by NASA Goddard Land Assimilation System,the land cover information and remotely sensed vegetation index are integrated to produce dynamic surface roughness length and zero plane displacement height.Sensitivity analysis is done for the input parameters of the improved SEBAL model.The study shows that the model is more sensitive to LST,Albedo,and NDVI,while the win speed and the momentum roughness length are relatively low sensitive parameters.As a whole,the model is more stable.The retrieval evapotranspiration by the model with input parameters change a certain amount are not in signigicant change.The analysis of the impact of the ET results simulated by the model in combination with terrain factors (altitude,slope,aspect)show that the ET results will overestimate about 30%in high altitude and shady slope region if the terrain is not taked into account.3)The idea of Spatial Local Similarity is introduced to improve the Thermal Enhance method of Kustast et al,which is used to enhance the spatial resolution of 1km MODIS LST and Albedo to 250 m utilizing the spatial details of 250 m MODIS vegetation index.Herein,this paper makes full use of the advantages of the temporal and spatial resolutions of MODIS data to constructe day-to-day driving data for the regional water and heat model,which meet the requirements of spatial heterogeneity scale,making the higher frequency of large area water/heat flux monitoring has a good operational.Verification of ET estimated by the model in different time scales suggests that the mean relative errors are about -11.34%,-6.30%for daily and weekly time scale,and approximately less than 4%for monthly or seasonal scale,respectively.The simulation results of the remote sensing model are in good agreement with the in situ observation.4)With modeling results,the spatial and temporal patterns of water/heat in study areas have been monitored and discussed.The regional ET both appears to be largest in summer,followed by the spring and autumn minimum for 2005 and 2006 year.In spring,low ET value areas are mainly located in hilly areas within middle-south of Shandong and Shandong Peninsula area,while the high ET value areas are mainly distributed in some large water reservoirs and the Northwest and Southwest plains of Shandong where crops grow better.Although the vegetation coverage is not high in Yellow River Delta region,there also has higher ET value due to shallow depth of the water table of the area.In summer,all the study area have a higher level of ET.High-value areas are mainly distributed in large bodies of water,reservoirs,irrigated regions besided the two sides of Yellow River and coastal beach.Low-value regions are mainly located in hilly areas within middle-south of Shandong and man-made areas such as urban.The whole area have lower level of ET in autumn.Meanwhile,the retrieval results demonstrate that the regional ET possessed evidently positive correlation with the vegetation coverage versus negative correlation with LST.5)Finally,the monthly changes of ET during 2005～2006 for different land use/ land cover(LULC)types have been analyzed.It is found that all the monthly average ET show largest in water areas,followed by paddy fields,then by woodlands,dry fields and grasslands,urban and built-up minimum.Water surplus and deficiency of LULC in different month are also discussed by combined with precipitation data.Regional water stress index(RWSI)is extracted using actual and potential ET based on regional ET remote sensing model to monitor the regional drought dynamicly in 2005 and 2006 autumn.The results are reasonable and credible in general,and the application and pending need to be confirmed with further studies.