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K. W. Oleson, G. B. Bonan, J. Feddema, and M. Vertenstein

simulations produce similar results, with urban effects being largest in summer and smallest in winter and about equal for spring and autumn. Karl et al. (1988) attributed the smaller effects in spring partly to the lower anthropogenic heating in spring as compared with winter. However, our study does not include anthropogenic fluxes, and therefore this explanation is not tested. The daily average maximum heat island for all grid cells ranges from about 1.5° to 5°C, depending on height-to-width ratio

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K. W. Oleson, G. B. Bonan, J. Feddema, M. Vertenstein, and C. S. B. Grimmond

1. Introduction Land use/land cover change is increasingly being recognized as an important yet poorly quantified component of global climate change ( Houghton et al. 2001 ). Land use/land cover change mechanisms include both transformation of natural land surfaces to those serving human needs (i.e., direct anthropogenic change; e.g., conversion of tropical forest to agriculture) as well as changes in land cover on longer time scales that are due to biogeophysical feedbacks between atmosphere

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M. Baldi, G. A. Dalu, and R. A. Pielke Sr.

; presence of heterogeneities in surface conditions such as dry land adjacent to wet land or alternating dry and wet patches) are important since they affect the partitioning between latent and sensible heat fluxes. Roy and Avissar (2002) found that coherent mesoscale circulations were triggered by surface heterogeneities in Amazonia. Otterman (1977 , 31–41) speculated that anthropogenic changes from bare soil to a complex vegetated surface in regions of marginal rainfall can favor convective

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Young-Kwon Lim, Ming Cai, Eugenia Kalnay, and Liming Zhou

1. Introduction Global mean surface temperature time series derived from in situ observations reveal the interdecadal global warming over the last several decades ( Houghton et al. 2001 ). Many studies reported that this upward trend is significantly a result of primary human impacts such as greenhouse gases ( Houghton et al. 2001 ) and land use ( Pielke et al. 2002 ). The anthropogenic land-use impact on surface warming may become more important as the surface vegetation changes in the form of

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