Study On The Effects Of Urban Land Use Change On Thermal Environment Based On SLEUTH And WRF Models

Rapid urbanization and increasing built-up land has caused gradual changes in the pattern of urban thermal characteristics.The increase of anthropogenic heat has also intensified the urban heat island,threatening the livability and sustainability of the city.The impacts of urban development on the thermal environment have attracted attention,and the issue of how to reduce the impacts has become very topical.Taking Nanjing and its surrounding region as the study area,and based on an analysis of the potential of urban development and ecological constraint factors in the study area,we firstly analyzed the land suitability;and then used SLEUTH(Slope,Land use,Excluded,Urban,Transportation and Hillshade)model to predict the urban growth to 2040.At the same time,we used the WRF(Weather Research and Forecast)model to simulate the thermal environment under different urban growth scenarios,then investigated the resulting impacts on the urban thermal environment from land use change under different development scenarios.The results will help to understand the potential impact of urban growth on the urban thermal environment and provide a good reference for planning urban development to ensure a livable and sustainable city.This research is divided into five chapters.The first chapter introduces the research background and significance,reviews the related previous studies,and sketches out the basic framework of this research.The second chapter introduces the case study area and provides a detailed description of the data capturing and data preprocessing.The third chapter focuses on the urban space expansion simulations under different scenarios.We analyzed the land suitability and divided it into different urban development scenarios according to different development concepts,and then simulated urban growth to 2040 using the SLEUTH model.The fourth chapter presents an analysis of the impact of land use change on the thermal environment based on the WRF model.We investigated the urban thermal environment simulation using the land use in 2013 as a baseline and then simulated land use scenarios using the SLEUTH model respectively to instead of the original land use used in WRF model,and then analyzed the pattern of thermal environment characteristics under different urban growth scenarios to study how the land use change affects the urban thermal environment.The fifth chapter summarizes the main conclusions and innovations of this research,discusses the limitations,and suggests some areas for future research.The main conclusions are as follows:(1)The accuracy of the reconstruction of urban expansion using the SLEUTH model is about 87.91%.The "edge-growth" and "filling in growth" are the main urban growth forms,but the "frog leap" growth also occurred as new urban development centers on the outskirts of the city.In S3(the lowest ecological security),urban development has the highest intensity,while in S1(the highest ecological security),the urban growth area is the smallest and then is S2(the medium security).With increasing urban expansion,the aggregation of built-up land is constantly increasing,and as a result,agricultural land and green spaces become more and more fragmented.Landscape diversity and heterogeneity reduce and the landscape is becomes homogeneous.The results indicate that the implementation of an ecological protection strategy could effectively avoid disordered urban sprawl and the erosion of urban ecological land(green spaces,agriculture land and water).(2)The WRF model simulated the changes in the urban thermal environment well.After revising the land use with the 2013 instead of the original data,the validation of air temperature indicated that the average error is-0.2℃,while RMSE is 1.24 and correlation coefficient(r)is 0.94.If using the original data,the average error of-0.6 ℃,RMSE is 1.25 and correlation coefficient(r)is 0.95.The accuracy of the simulated air temperature(2m above the ground)is improved by using the latest land-use data,and the simulated temperature is closer to the observed temperature.Urbanization has led to the significant increase in air temperature especially the air temperature above the new built-up land.The area of high temperature increases together with the expansion of built-up land,and the intensity and duration of the urban heat island are also increasing.(3)Urban land use change is an important factor causing the change in the thermal environment.Urbanization is increasing the average air temperature of the study area.The air temperature above built-up land rises more significantly than all of the other areas.Compared with green land and bare land,the loss of the agricultural land is the greatest,which has an obvious influence on the increase in air temperature.The high temperature areas continues expanding to the south and east of the study area,and results in the original insolated high temperature areas gradually integrated and merged into a larger high-temperature region.S3 has the biggest high temperature area which accounts for 41.97%of the study area,increasing by 1456.59 km2 compared with that in 2013.The developing patterns of secondary high temperature area and high temperature area are consistent with that of expanding built-up land.Low temperature area,secondary lower temperature area and medium temperature area are constantly decreasing.According to the changes of thermal landscape pattern,low temperature areas and the secondary lower temperature areas are tending to disappear,with the degree of aggregation decreasing.The medium temperature patches are becoming fragmented.The dominance,aggregation and integrity of high temperature area are gradually increasing.The growth of built-land results in the heat increasingly concentrating and aggregating.The urban thermal environment is worsening.At the landscape level,the index of CONTAG and AI is lower in 2013,indicating a higher fragmentation.S1 has a higher landscape diversity and the patches are distributed evenly compared with S2 and S3.In S2 and S3,the range of high temperature expands continuously,and many secondary higher temperature patches changed into high temperature patches.The high temperature areas become the dominant landscape patches.In S3,the index of CONTAG and AI all become the largest,with the best connectivity and aggregation.Landscape diversity and heterogeneity decreased most with simple thermal landscape type.The results of the research indicated that the changes of land use under different urban expansion scenarios will result in very different impacts on the urban thermal environment.Planning urban development based on the predictions of urban expansion and the simulated urban thermal environment will ensure the development of a livable and sustainable city.