Synergistic Interactions Between Urban Heat Island And Heat Waves And Spatially Explicit Mapping Of Heat Health Risk

The increase in the frequency and intensity of extreme heat events(EHEs)and urban heat island(UHI),potentially associated with climate change and unprecedented process of urbanization in the near future,highlight the importance of exploring the synergistic interaction between UHI and EHEs and also heat health risk assessment,which is an important starting point for heat-related mortality reduction and sustainable development at regional scale.Based on the meteorological data,multi-sensor remote sensing data and demographic and socioeconomic statistical data,this paper detected the spatial-temporal variation of city-scale UHI intensity in the Yangtze River Delta and quantitatively analyzed the synergistic interaction between heat waves and UHI during 2013.Moreover,the heat-related health risk was spatially explicitly assessed and mapped at the 250 m × 250 m pixel level across Yangtze River Delta.The results showed that:(1)The annual mean urban heat island intensity in Shanghai was significantly higher than that in Hangzhou and Nanjing in 2013,and its seasonal variation was characterized by higher intensity in warm season.Diurnal UHI intensity and the urban mean land surface temperature(LST)showed a clockwise distribution from January to December,while nocturnal UHI intensity showed non-significant variation through the year.(2)UHI intensity of all three cities were exacerbated during heat waves and was linearly related to urban surface temperature.With the increase of urban LST,diurnal UHI of Shanghai,Hangzhou and Nanjing increased at 0.142?/?,0.127?/? and 0.102?/? respectively.The rising rate of UHI intensity slowed down at night,which increased at 0.138?/? and 0.108?/? in Shanghai and Hangzhou respectively,but there was no significant relationship between nocturnal UHI and urban LST in Nanjing.(3)The temperature difference between urban areas and the other land cover types during heat waves was significantly higher than that during non-heat wave days.Low daytime LST were mainly found in water and woodland,while nighttime LST of water was higher than that of the urban area,which was more significant during heat waves period.(4)A visual inspection suggests that the high risk areas were found distributed mainly in urbanized areas of Yangtze River Delta,including the downtown of Shanghai,Jiangsu,Changzhou,Hangzhou,Hangzhou,Ningbo,Wuxi,Jiaxing and Taizhou,which were seemingly driven by the human exposure and hazard distribution.In lower tier cities and suburbs of upper tier cities,the heat risk patterns were also coupling driven by the geographic variations of heat vulnerability,while the heat risk patterns in some relatively less developed areas were mainly driven by both high hazard and vulnerability distribution.