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

Abstract

Previous investigations of urban heat islands (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 (WS), and basic land‐use categories modified from local climate zones (urban/suburban), in Birmingham, United Kingdom. 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 WS conditions. Results also demonstrate better confidence in the approach for summer and spring seasons, and for more urbanized 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 transferable to other cities and/or can be used to guide further research to explore the sUHII‐aUHII relationship under other environmental conditions.

A tale of two cities: The influence of urban meteorological network design on the nocturnal surface versus canopy heat island relationship in Oklahoma City, OK, and Birmingham, UK

“…From the perspective of statistics, slope and R 2 value are closely related to covariance between sUHII and aUHII ( cov ( sUHII , aUHII )). Stronger joint variability between sUHII and aUHII could cause the increase of covariance, which indicates the weaker advection effect on the UHII (Feng et al ., 2019). Therefore, the larger cov ( sUHII , aUHII ) shown in Table 4 is statistically responsible for the higher R 2 value (defined as the standardized covariance) and slope in OKC.…”

“…The larger rate of change of aUHII with respect to sUHII in OKC is potentially attributed by the weaken advection effect on the sUHII ‐ aUHII relationship. Advection effect could increase the disparity between sUHII and aUIII (Feng et al ., 2019), which is represented by the lower cov ( sUHII , aUHII ) in Birmingham (Table 4), leading to the smaller slope and reduced R 2 in the regression model. The underlying mechanism for these results could be the traffic light siting of the stations in OKC within the street canyon.…”

“…Regarding the spatial consistency between satellite data and ground observation, a simple correction scheme based on inverse distance weighting with 500‐m buffer as used in Feng et al . (2019) is implemented for each station. The overpassing time for the Aqua and Terra satellites occurs approximately at 01:30 a.m. and 22:30 p.m. local solar time over both OKC and Birmingham, respectively, which is considered appropriate for this study.…”

“…However, according to Feng et al . (2019), the high correlation between T s and T a could be attributed to the large variation of background temperature. aUHII estimated from the empirical relationship between T s and T a might be lack of confidence to further compare with sUHII .…”

“…In a previous paper by the authors (Feng et al . (2019)), a unique analysis combining linear regression with confidence ellipse, together with two statistical tests, provides a starting point to generalize patterns of the sUHII ‐ aUHII relationship across cities. This study uses this approach to provide a comparative study of the nocturnal sUHII ‐ aUHII relationship in Oklahoma City (OKC), OK, and Birmingham (BHAM), UK, by using MODIS satellite data and ground observations from two UMNs.…”