Saturday, July 18, 2015

Urban Climate

A recent journal article by MZ Jacobson et al points out some of the climatological impacts of urbanization on local climate. The land use change that urbanization leads to is known to impact climatological conditions through changes in soil moisture evaporation, transpiration (evaporation from plants), heat absorption and advection (wind).

In this article the authors used models to study the impact of the change in urban extent in Beijing. Beijing provides a good case due to the extreme nature of changes there - the urban extent of the city quadrupled between 2000 and 2009.

Key Points from the article:

  • Beijing's expansion created a ring of impact in the new portion of the city
  • Without considering the impact of more vehicles and other sources of human caused polution - urbanization's impact on climatological conditions alone slowed winds and increased pollution vertical dilution and increased ground level temperature, and ozone

Interestingly the authors used crowdsourced data on road surface area in their study.

Take homes:
This study found that urbanization changes local climate in these ways - it:

  • increases ground level temperature
  • decreases ground level humidity
  • decreases horizontal movement of air (wind, advection)
  • increases vertical movement of air (convection)
  • reduces reflectivity of the surface (albedo) causing the retention of more solar energy
These impacts:

  • decreased surface pollution by promoting vertical mixing
  • but increased surface ozone (O3) due to other changes in the chemical profile of the air
None of these impacts takes into account vehicle use or other pollution sources.

Mark Z. Jacobson, Son V. Nghiem, Alessandro Sorichetta and Natasha Whitney
Article first published online: 19 JUN 2015 | DOI: 10.1002/2014JD023008

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