Impact of atmospheric conditions and levels of urbanisation on the relationship between nocturnal surface and urban canopy heat islands

Previous investigations of urban heat island (UHI) are primarily focused either on the canopy heat island intensity (aUHII) derived from weather stations, or on the surface urban heat island intensity (sUHII) derived from satellite instruments. Research of the relationship between sUHII and aUHII (the sUHII-aUHII relationship) is limited and this study attempts to further progress this possibility by examining the night-time sUHII-aUHII relationship for three factors: season, wind speed, and basic landuse categories modified from local climate zones (urban / suburban), in Birmingham, UK. Using high resolution datasets of canopy air temperature from Birmingham Urban Climate Laboratory and land surface temperature from the MODIS instrument aboard the Terra and Aqua satellites, with a unique methodology of regression analysis, confidence ellipse analysis of covariance (ANCOVA), and 2-D Kolmogorov-Smirnov (K-S) tests, statistical evidence is provided to present the varying patterns and magnitudes between sUHII and aUHII. The significance of the impact of the three considered factors is clearly supported by the statistical tests. The results indicate that satellite data can be used to infer aUHII with a higher confidence for low wind speed conditions. Results also demonstrate better confidence in the approach for summer and spring seasons, and for more urbanised sites. Indeed, the analysis potentially indicates that wind advection is a key factor for the investigation of the sUHII-aUHII relationship. Overall, the methods used here are transferrable to other cities and/or can be used to guide further research to explore the sUHII-aUHII relationship under other environmental conditions.