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
3.
cropland
4.
horticulture farms
5.
dike-pond land
6.
forest
7.
water
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.
Results
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.
Conclusion
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.
I think the effects urbanization can have surface temperatures of an area is both fascinating and terrifying. I'm sure there are numerous reasons as to why urbanization has these effects. For example, the lack of vegetation in these urban areas, along with the pavement and buildings severely affect not only the albedo rates of the area, but the wind currents as well as key parts of the hydrological cycle are affected too. The buildings restrict air flow throughout the area and the paved roads absorb more sunlight while preventing adequate water infiltration/percolation. And because, as we say in environmental studies: "everything is connected", these seemingly unrelated events can have drastic consequences. Using GIS in this particular instance is just more evidence supporting the idea that the anthropogenic effects we humans have on the natural world are real and they are not negligible.
ReplyDeleteThis is one reason why sustainable development is needed, or low impact urbanization. Simple solutions exist, for example having roads that are made with white concerte as opposed to black asphalt. The white reflect more sunlight causing less surface heat, while black asphalt absorbs more solar radiation. Other solutions are green roofs, or planting vegetation on top of buildings. This also helps in reducing urban heath islands through photosynthesis. The major road block to these solutions is money. The costs for sustainable development is higher then conventional development. How do you get developing nations to pay these extra costs? Some suggest Technology Transfer, or providing technology for free, other suggest subsides from rich to poor nations, and other suggest a credit system, where people pay taxes to provide monies for development (ie carbon credits and other ecological credits). These economic solutions focus on try to make the costs less, however an international agreement has not come about for this. Many a scared of global taxing and in a way global governance. I think what it really comes down to is values. If people have values that we should protect the environment, then they will pay more to maintain these values. You see this with great success with the LEED program, which is adopted international in many countries. However to change the hearts and minds of people, they need to see the impacts conventional development has. This study and other studies like these that use GIS/RS to measure the environment are important to provide the evidence for policy makers and the general public. What would have been a nice addition to this study, to take it further, is to model what would the heat island impacts would have been if sustainable development solutions were used instead. For example model home many degrees difference installing white roads instead of black roads would make. Or model the impact of green roofs. This way benefits can be associated with the higher costs, perhaps justifying costs or using scarce resources for sustainable development in better ways.
DeleteThe many effects of urbanization is a hot topic of interest to me. Not only are there social, economic, and health issues, but obviously many environmental problems associated with urbanization as well. It's not surprising though that a land covered in concrete and black asphault with a million cars on top of it is going to be much less pleasant than a forest or country side. It is also interesting to see the data on the expansion of agriculture and temperature rises since expansion of agriculture also degrades the land. Sustainable Urbanization 101: Plant more trees in parking lots, dammit! Haha, maybe we should present this paper to Georgetown City Council. :P
ReplyDeletePerhaps someone can do the same methods outlined on this paper, but do it on Georgetown and show the effects of recent urbanization. Perhaps the model a business as usual for the next decade of development, and sustainable development for the next decade, and find out the benefits is the city adopts green standards, like LEED certification for all new development.
DeleteThis topic is of great importance to the global climate change issue, and has influenced people to start planting more trees. It is amazing how far out the heat is spread when compared to the locations of urban growth. The only thing that makes me questions the severity of this map is that fact that the study took place in China, which is immensely over populated (possibility for skewed data). However the correlation between urban growth and high heat index is easily pointed at the lack of vegetation such as trees. Like Elise said we have way too much concrete and asphalt that there is no way that the earth could not be hot.Along with the Earth having many "hot spots" due to development there are other issues we are faced with, like weird weather patterns and changes in normal temperature for various geographical locations. So we should use GIS to map out the entire world compare the heat changes, compare them to changes in weather patterns, and make a change to how we are living.
ReplyDeleteGlobal mapping is still a few years away for desktop applications. Right now to map the world with this level of detail will take a really powerful computer. However doing this on a local level can have a bid discoveries, so consider doing it for Georgetown.
DeleteThanks for sharing, nice post! Post really provice useful information!
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