Wednesday, December 9, 2009

Expanding cities could increase warming

Belle Dumé in Environmental Research Web: Urban heat islands – city areas that are warmer than surrounding countryside – could adversely influence climate in certain regions of the world, especially in countries like China where the economy is growing fast and cities are getting bigger. This critical but often ignored aspect of regional climate change should be taken into account when developing new models, say researchers in Beijing.

The amount of green vegetation cover in a region directly influences local climate by affecting how water and heat are exchanged between the land and atmosphere. However, understanding such interactions – especially in humid, subtropical areas – remains a challenge.

Now, Gensuo Jia of the Institute of Atmospheric Physics at the Chinese Academy of Sciences and colleagues have analysed how changing vegetation cover in urban and rural areas in the Pearl River Delta region of south-east China affects local climate. The region has seen rapid economic development in recent years, which has dramatically altered the landscape; formerly green, lush areas are now covered over with concrete. These changes can be clearly identified with the Terra moderate resolution imaging spectrometer (MODIS).

…Jia's team examined the change in area of urban, wild land and urban–rural fringes from 2000–2008. The results showed that more photosynthesis occurs in the wild lands and stable urban landscapes than the urban–rural fringe areas, where cities are now expanding and there is less and less greenery.

…"Vegetation is an important driving factor in local climate dynamics," says team member Yonghong Hu of the Institute of Atmospheric Physics. "It influences how much solar radiation is absorbed, surface and air temperatures, and the amount of water evaporating from land."...

Manhattan's Union Square around 1910

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