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. 2015 Jun 10;5:11160.
doi: 10.1038/srep11160.

The Footprint of Urban Heat Island Effect in China

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Free PMC article

The Footprint of Urban Heat Island Effect in China

Decheng Zhou et al. Sci Rep. .
Free PMC article

Abstract

Urban heat island (UHI) is one major anthropogenic modification to the Earth system that transcends its physical boundary. Using MODIS data from 2003 to 2012, we showed that the UHI effect decayed exponentially toward rural areas for majority of the 32 Chinese cities. We found an obvious urban/rural temperature "cliff", and estimated that the footprint of UHI effect (FP, including urban area) was 2.3 and 3.9 times of urban size for the day and night, respectively, with large spatiotemporal heterogeneities. We further revealed that ignoring the FP may underestimate the UHI intensity in most cases and even alter the direction of UHI estimates for few cities. Our results provide new insights to the characteristics of UHI effect and emphasize the necessity of considering city- and time-specific FP when assessing the urbanization effects on local climate.

Figures

Figure 1
Figure 1. Locations of the 32 major cities in China.
All of the cities are municipalities or provincial capitals except Shenzhen, which is China’s first special economic zone, and is now considered one of the fastest-growing cities in the world. The red areas on the map were included in this analysis, which excluded the altitude effects and water pixels. BJ: Beijing; CC: Changchun; CS: Changsha; CD: Chengdu; CQ: Chongqing; FZ: Fuzhou; GZ: Guangzhou; GY: Guiyang; HK: Haikou; HZ: Hangzhou; HB: Harbin; HF: Hefei; HT: Hohhot; JN: Jinan; KM: Kunming; LZ: Lanzhou; LS: Lhasa; NC: Nanchang; NJ: Nanjing; NN: Nanning; SH: Shanghai; SY: Shenyang; SZ: Shenzhen; SJZ: Shijiazhuang; TY: Taiyuan; TJ: Tianjin; UQ: Urumqi; WH: Wuhan; XA: Xi’an; XN: Xining; YC: Yinchuan; ZZ: Zhengzhou. Map was generated using ArcGIS 9.3 (www.esri.com/software/arcgis).
Figure 2
Figure 2. The delineation of urban area and twelve buffer zones, an example of Beijing.
Landsat TM false color image acquired in Sep 3rd 2005 with a spatial resolution of 30 m × 30 m (A), daytime land surface temperature (LST) (B), and nighttime LST (C) in 2005. The black line stands for the border of urban area, the land within the border was considered as urban area, and the white lines represent the border of buffers (each of them covers half of actual urban area). Pixels that were water body or with elevation more than 50 m higher than the highest point in urban area were excluded from this analysis. Maps were generated using ArcGIS 9.3 (www.esri.com/software/arcgis).
Figure 3
Figure 3. Trends of urban heat island effect (△T, defined as the LST differences relative to unaffected rural areas) from urban to rural areas during the day for China’s 32 major cities averaged over 2003–2012.
The error bars represent the standard deviation.
Figure 4
Figure 4. Exponential trends of the △T with distance (d) away from urban to rural areas for China’s 32 major cities averaged over 2003–2012.
The function takes form of △T = A × e−S×d + T0, where A indicates the maximum temperature difference, S is the decay rate, and T0 is the asymptotic value that the exponential trend can reach.
Figure 5
Figure 5. Trends of △T from urban to rural areas during the night for China’s 32 major cities averaged over 2003–2012.
The error bars represent the standard deviation.
Figure 6
Figure 6. The footprint of urban heat island effect (FP, times of urban area) for China’s 32 major cities averaged over 2003–2012.
The hollow black circle indicates no significant urban heat island effect for the city (NS). Maps were generated using ArcGIS 9.3 (www.esri.com/software/arcgis).
Figure 7
Figure 7. Box and whisker plots for annual, summer, and winter FPs during daytime and nighttime over China’s 32 major cities.
The boxes represent the 25% to 75% range, the whiskers indicate the minimum and maximum values, and the open pentagrams demonstrates the mean values.
Figure 8
Figure 8. Relationship between the areas of the FP and actual urban land cover across China’s 32 major cities.
The relationship was not significant during daytime in winter (panel B) because 15 of 32 cities have no UHI effect (shown as empty circle), but the correlation was significant at 0.01 level if we excluded those cities with no UHI effect.
Figure 9
Figure 9. Relationship between annual mean urban-rural and urban-suburban LST differences averaged over 2003–2012 across China’s 32 major cities.

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