The Impacts of the Uncertainties of Land Surface Information on the Urban Heat Island Attribution Analysis in the Yangtze River Delta Urban Agglomeration, China

Variations in land biogeophysics and human activity in urban environment caused by urbanization significantly change surface energy budgets, thus acting on local weather and climate, resulting in typical urban climates such as urban heat island (UHI), which leads to more severe urban heat stress. UHI mitigation strategies are critical since increasing heat stress brings great challenges to socio-economic, energy consumption and human health. However, the consistency of the urban expansion range among different land-use datasets is less than 50% in China, and the uncertainty of urban land unit will inevitably have a great impact in the numerical simulation of UHI. Four typical sets of land-use datasets were used to drive the Community Land Model (CLM) to investigate the impacts of the uncertainty of surface heterogeneity on UHI and quantitative attribution of UHII in the Yangtze River Delta Urban Agglomeration (YRDUA), the study shows the uncertainty of urban expansion in different land-use datasets mainly affect the spatial distribution of UHI, and the uncertainty of vegetation plays a leading role in UHII, especially in forested regions where UHII is more prominent. Furthermore, we use the intrinsic biophysical mechanism (IBM) method and the two-resistance mechanism (TRM) method, two widely used attribution methods of UHII, to investigate the various contributions of UHII in the YRDUA as well as the similarities and differences of the UHII dominated mechanism between IBM and TRM method. The IBM method show that most important contribution of daytime UHII in the YRDUA is aerodynamic resistance (i.e. variations in the efficiency of heat convection from the surface to the lower atmosphere between urban and rural areas), followed by evaporative cooling contribution resulted from the variations in the Bowen ratio. The TRM method indicates that evaporation cooling related to surface resistance largely interprets geographic variations of daytime UHII, and aerodynamic resistance contribution is next. However, the attribution results of these two methods are consistent on nighttime UHII, mainly controlled by the variations in heat storage of urban and rural areas.