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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, D09117, doi:10.1029/2006JD007505, 2007

Observational estimates of radiative forcing due to land use change in southwest Australia

Udaysankar S. Nair

Earth System Science Center, National Space Science and Technology Center, University of Alabama, Huntsville, Alabama, USA


Deepak K. Ray

Department of Atmospheric Sciences, University of Alabama, Huntsville, Alabama, USA


Jun Wang

Department of Atmospheric Sciences, University of Alabama, Huntsville, Alabama, USA


Sundar A. Christopher

Department of Atmospheric Sciences, University of Alabama, Huntsville, Alabama, USA


Tom J. Lyons

School of Environmental Science, Murdoch University, Murdoch, Western Australia, Australia


Ronald M. Welch

Department of Atmospheric Sciences, University of Alabama, Huntsville, Alabama, USA


R. A. Pielke Sr.

Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado, USA


Abstract

Radiative forcing associated with land use change is largely derived from global circulation models (GCM), and the accuracy of these estimates depends on the robustness of the vegetation characterization used in the GCMs. In this study, we use observations from the Clouds and Earth's Radiant Energy System (CERES) instrument on board the Terra satellite to report top-of-the-atmosphere (TOA) radiative forcing values associated with clearing of native vegetation for agricultural purposes in southwest Australia. Over agricultural areas, observations show consistently higher shortwave fluxes at the TOA compared to native vegetation, especially during the time period between harvest and planting. Estimates using CERES observations show that over a specific area originally covered by native vegetation, replacement of half the area by croplands results in a diurnally averaged shortwave radiative forcing of approximately −7 W m−2. GCM-derived estimates for areas with 30% or more croplands range from −1 to −2 W m−2 compared to observational estimate of −4.2 W m−2, thus significantly underestimating radiative forcing due to land use change by a factor of 2 or more. Two potential reasons for this underestimation are incorrect specification of the multiyear land use change scenario and the inaccurate prescription of seasonal cycles of crops in GCMs.

Received 12 May 2006; accepted 22 November 2006; published 15 May 2007.

Keywords: Australia; land use change; radiative forcing.

Index Terms: 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions (0426, 1610); 1631 Global Change: Land/atmosphere interactions (1218, 1843, 3322); 1632 Global Change: Land cover change; 1843 Hydrology: Land/atmosphere interactions (1218, 1631, 3322); 3359 Atmospheric Processes: Radiative processes.

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Citation: Nair, U. S., D. K. Ray, J. Wang, S. A. Christopher, T. J. Lyons, R. M. Welch, and R. A. Pielke Sr. (2007), Observational estimates of radiative forcing due to land use change in southwest Australia, J. Geophys. Res., 112, D09117, doi:10.1029/2006JD007505.