An Overview and Perspective about Causative Factors of Surface Urban Heat Island Effects

Abstract

Urban heat island(UHI) is a hotspot in the study about urban ecological and environmental effects.UHI effects are caused by multiple factors,and the synthesized mechanism study can supply a foundation to release the negative effects of UHI.This study proposes a theory framework for causative factors of surface urban heat island(SUHI) by analyzing the process of surface energy on the basis of landscape ecology.Since surface temperature represents the process of surface energy,we examine the causative factors of this process,which includes energy absorption/emission,energy translation,and energy transmission.The internal and external progresses on each kind of causative factors are reviewed in this study.We also compare the internal studies on synthesized mechanism of SUHI with external studies.By the comparison of progresses of causative factor studies and the mechanism of SUHI,we deduce the prospect on this field. The energy absorption and emission of surface represent the ability to absorb solar short-wave radiation,and the capacity to emit earth's surface long-wave radiation,which are controlled by the physical properties of land surface.The studies on this theme focus on land use and biophysical properties.It has reached a consensus on the functions of land use/land cover.The biophysical properties can better describe the relationship between surface characteristics and temperature with higher accuracy.The physical properties of the surface include vegetation,impervious surface,and surface moisture,which are represented by land cover indices derived from remote sensed data including NDVI,ISA,NDBI,NDMI,etc.Energy translation is the process of translating one form of energy into another,which,in this case,is surface heat determined by the intensity of human activities.Population density,energy consumption intensity,and automobile flux are normal indices to depict the intensity of human activities.However,the studies in this field are limited by the spatial resolution of social-economic data.Energy transmission represents the energy flow between different patches referring to the temperature gradient,which primarily depends on the spatial relationship between landscape patches.Two themes in this field have been developed.One is the relationship between temporal heterogeneity of landscape patterns and surface temperature changes.The other is the influence of spatial characteristics of landscape patches on surface temperature.In the field of synthesized causative factors,the external study focuses on the triangle model of temperature,vegetation,and soil moisture.Most of the internal analyses are about the statistical model consisted of land cover and social-economic components. There are two tendencies of the relating studies in the future.Firstly,high resolution data and field survey data will promote the study on the analysis of energy translation and transmission.Secondly,following a description of energy process,we can involve social-economic indicators and landscape patterns in the triangle mechanism model to establish the systemized mechanism of SUHI.