Q. Weng's study: "A remote sensing-GIS evaluation of urban expansion and its impact on surface temperature in the Zhujiang Delta, China" is fairly straightforward in its title, combining the use of remote sensing and GIS to determine how urban development has progressed and how it has changed surface temperatures in this delta region.
Zhujiang Delta is the third largest river delta in China, this study focuses on the central area of the region in the “cities/counties: Guangzhou, Panyu, Sanshui, Nanhai, Foshan, Shunde, Jiangmen, Zhongshan, Zhuhai, Xinhui, Doumen, Zengcheng, Dongguan, Baoan and Shenxhen” (Weng, 2000). The Delta has an average temperature of 21-23 degrees Celsius, and has fertile sediment deposits as well as 1600 – 2600 mm of rain a year, making it one of the most agriculturally production regions of China. It also holds some of China’s biggest cities such as Hong Kong and Macao and has seen much development that has changed its land use and land cover. This study uses GIS to analyze such changes and their “impact on surface temperature” (Weng, 2000).
Urban expansion detection and analysis
Land use/cover patterns were mapped for 1989 and 1997 using Landsat Thematic Mapper data. The land cover types identified are:
1. urban or built-up land
2. barren land
4. horticulture farms
5. dike-pond land
land use/cover changes were detected by collaborating quantitative areal data of gains and loses in each category between 1989 and 1997. Then, layers of city/county boundaries as well as major roads and major urban centers were overlaid and converted to raster format. 10 buffers of 500m each were put around one major road, the amount of urban expansion in each buffer zone was calculated to see the density of expansion in each buffer. These values were then used to see how distance from a road affects density of development.
Urbanization expansion impact analysis
There is a distinct relationship between land texture and surface temperature, using this relationship, Weng was able to determine the impact of urban development on surface temperature in Zhujiang Delta. Weng converted the digital number of the thermal infrared data into radiant temperatures. Then, corrections were made to this temperature due to that fact that different land types radiate different amounts of radiation and light. Land cover images and the temperatures of the land for each year between 1989 and 1997 were overlaid, allowing Weng to study the relationship between urbanized land use changes and temperatures.
During the 8-year study period, the area of urban/built-up land has increased by 47.68% and the area of horticulture farms has increased by 88.66%. Weng found that “most urban expansion (66%) can be observed within a distance of 2000m from a major road” (Weng, 2007), which helps decipher where development might happen in the future and where temperature increases are most likely to happen.
Of the land cover types, urban/built-up land is resulted to have the highest surface radiant temperature. Barren land follows as having the second highest surface radiant temperature. The lowest temperatures were found in forests, followed by water bodies, dike-pond land and cropland.
This study used remote sensing and GIS to evaluate rapid urban expansion and how it impacted surface temperatures in Zhujiang Delta. The study concluded that urban development increased between 1989 and 1997 in uneven parts of the delta, correlating with the placement of major roads. The study also found that urban development had a direct effect on the environment and raised temperatures by 13.01 K.
The increase of surface temperature was found to be related to decrease in biomass, and development (and therefore temperature increase) in one area was shown to have a direct effect on other areas, such as forests that had not been developed.
Weng, Q. "A Remote Sensing-GIS Evaluation of Urban Expansion and Its Impact on Surface Temperature in the Zhujiang Delta, China." International Journal of Remote Sensing 22.10 (2001): 1999-2014. Print.