Editorial Type:
Article
Article Type:
Research Article

An Urban Parameterization for a Global Climate Model. Part II: Sensitivity to Input Parameters and the Simulated Urban Heat Island in Offline Simulations

K. W. Oleson Climate and Global Dynamics Division, National Center for Atmospheric Research,* Boulder, Colorado

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G. B. Bonan Climate and Global Dynamics Division, National Center for Atmospheric Research,* Boulder, Colorado

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J. Feddema Department of Geography, University of Kansas, Lawrence, Kansas

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M. Vertenstein Climate and Global Dynamics Division, National Center for Atmospheric Research,* Boulder, Colorado

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Print Publication:
01 Apr 2008
Collections:
Impacts of Land Use and Land Cover Change on the Atmosphere
DOI:
https://doi.org/10.1175/2007JAMC1598.1
Page(s):
1061–1076
Restricted access

Abstract

In a companion paper, the authors presented a formulation and evaluation of an urban parameterization designed to represent the urban energy balance in the Community Land Model. Here the robustness of the model is tested through sensitivity studies and the model’s ability to simulate urban heat islands in different environments is evaluated. Findings show that heat storage and sensible heat flux are most sensitive to uncertainties in the input parameters within the atmospheric and surface conditions considered here. The sensitivity studies suggest that attention should be paid not only to characterizing accurately the structure of the urban area (e.g., height-to-width ratio) but also to ensuring that the input data reflect the thermal admittance properties of each of the city surfaces. Simulations of the urban heat island show that the urban model is able to capture typical observed characteristics of urban climates qualitatively. In particular, the model produces a significant heat island that increases with height-to-width ratio. In urban areas, daily minimum temperatures increase more than daily maximum temperatures, resulting in a reduced diurnal temperature range relative to equivalent rural environments. The magnitude and timing of the heat island vary tremendously depending on the prevailing meteorological conditions and the characteristics of surrounding rural environments. The model also correctly increases the Bowen ratio and canopy air temperatures of urban systems as impervious fraction increases. In general, these findings are in agreement with those observed for real urban ecosystems. Thus, the model appears to be a useful tool for examining the nature of the urban climate within the framework of global climate models.

* The National Center for Atmospheric Research is sponsored by the National Science Foundation

Corresponding author address: Keith Oleson, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307-3000. Email: oleson@ucar.edu

This article included in the Impacts of Land Use and Land Cover Change on the Atmosphere special collection.

Abstract

In a companion paper, the authors presented a formulation and evaluation of an urban parameterization designed to represent the urban energy balance in the Community Land Model. Here the robustness of the model is tested through sensitivity studies and the model’s ability to simulate urban heat islands in different environments is evaluated. Findings show that heat storage and sensible heat flux are most sensitive to uncertainties in the input parameters within the atmospheric and surface conditions considered here. The sensitivity studies suggest that attention should be paid not only to characterizing accurately the structure of the urban area (e.g., height-to-width ratio) but also to ensuring that the input data reflect the thermal admittance properties of each of the city surfaces. Simulations of the urban heat island show that the urban model is able to capture typical observed characteristics of urban climates qualitatively. In particular, the model produces a significant heat island that increases with height-to-width ratio. In urban areas, daily minimum temperatures increase more than daily maximum temperatures, resulting in a reduced diurnal temperature range relative to equivalent rural environments. The magnitude and timing of the heat island vary tremendously depending on the prevailing meteorological conditions and the characteristics of surrounding rural environments. The model also correctly increases the Bowen ratio and canopy air temperatures of urban systems as impervious fraction increases. In general, these findings are in agreement with those observed for real urban ecosystems. Thus, the model appears to be a useful tool for examining the nature of the urban climate within the framework of global climate models.

* The National Center for Atmospheric Research is sponsored by the National Science Foundation

Corresponding author address: Keith Oleson, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307-3000. Email: oleson@ucar.edu

This article included in the Impacts of Land Use and Land Cover Change on the Atmosphere special collection.

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