The Cooling Effect Of Urban Waterbody Landscape

The rapid urbanization process has brought tremendous pressure to the urban ecological environment.Under the background of global warming,urban climate problems are particularly serious.Especially in hot summer weather,the increasing urban heat island(UHI)effect threaten the physical and mental health of urban residents.Utilizing urban cold island(UCI)to reduce the surrounding temperature is one of the most effective ways to mitigate the UHI.Various types of water bodies and wetlands are important components of UCI.They have great potential in regulating urban microclimate,improving urban thermal environment and alleviating urban heat stress.Understanding the relationship between urban water body and the thermal environment is crucial to the effective protection and maximization of the water cooling effects.It will help to improve the quality of urban climatic environment,and promote the healthy development of green cities.Wuhan,a big city with aboundant surface water resources in urban areas,is selected as the case study.The objective of this research is to protect and utilize the cooling effect of urban water bodies under hot summer weather condition.Quantitative techniques such as remote sensing technology,spatial analysis of geographic information system and landscape ecology pattern analysis are employed.The heterogeneity of thermal environment within urban areas is distinguished by using the local climate zone(LCZ)framework.Combining the cooling effect analysis of typical water bodies and the thermal effect analysis of urban water distribution,the cooling effect of urban water bodies is comprehensively studied,and the optimization strategies for urban water body and various types of urban land use are put forward.The thesis consists of 7 chapters.The background of this study and the research framework are introduced in the first chapter.The second chapter constructs the frame of thermal environmental heterogeneity by classifying the urban surface into different zones.The relation between air temperature(AT)and land surface temperature(LST)are examined in the third chapter.Taking typical water bodies as objects,the fourth chapter analyses the water cooling effects and the influence factors.The impact of urban water spatial distribution on the local thermal environment is investigated in the fifth chapter.Based on the analysis results of previous chapters,the optimizing suggestions are put forward in the sixth chapter.The last chapter summarizes this research and suggests the further study.The main conclusions of this research are as follow:(1)The LCZ framework has a good distinction between the heterogeneity the surface thermal environment in Wuhan.Water is the most typical category with low temperature in Wuhan.With a wide spatial distribution,Water has great potential to regulate the urban thermal environment.The landsacape metrices of Water impact the land surface temperature significantly at both patch and landscape level.(2)The positive relationship between air temperature(AT)and land surface temperature(LST)is very significant when the urban environment is relatively homogeneous.Both the AT and the LST increase as the distance from the river bank.However,the increase of AT is slower and smoother than that of LST.(3)The cooling effect of typical water bodies in Wuhan is remarkable.The water cooling effect is influenced by not only the water body situation,but also the landscape composition and configuration of surrounding landscpaes.The cooling potential,cooling intensity and cooling distance of big water bodies are generally greater than that of small ones.The water cooling distance in Wuhan is approxmately 900 m.It is worthy to notice that the water cooling effect varies arcoss different LCZ types.(4)The spatial distribution of urban water bodies impact the LSTs significantly.The gravity water index(GWI),taking both area and distance into accout,explains the LST variation well at various analysis scales.The spaial error model(SEM)is an appropricate model to analysis the water-LST relationship because the neighboring effect of LST is captured by SEM.The thermal impact of water distribution varies across different LCZ types.(5)It is essential to protect the coastline of urban water bodies strictly.Buffer zones should be set up with urban greening.Furthermore,designating areas surrounding water bodies is important and rational planning guidance is necessary.Different types of land use in cities should also be rationally planned and designed according to their specific response to the water cooling effect.The conclusions of this research can provide scientific basis for the urban planning and optimization of urban water bodies and surrounding area in Wuhan.Also,it can be case reference for other cities with aboundant surface water resources.It can surpport decision-making for alleviating urban heat island,improving the quality of urban ecological environment and guiding the green development of cities.