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[1] Land use/cover change has been recognized as a key component in global change. Various land cover data sets, including historically reconstructed, recently observed, and future projected, have been used in numerous climate modeling studies at regional to global scales. However, little attention has been paid to the effect of land cover classification accuracy on climate simulations, though accuracy assessment has become a routine procedure in land cover production community. In this study, we analyzed the behavior of simulated precipitation in the Regional Atmospheric Modeling System (RAMS) over a range of simulated classification accuracies over a 3 month period. This study found that land cover accuracy under 80% had a strong effect on precipitation especially when the land surface had a greater control of the atmosphere. This effect became stronger as the accuracy decreased. As shown in three follow-on experiments, the effect was further influenced by model parameterizations such as convection schemes and interior nudging, which can mitigate the strength of surface boundary forcings. In reality, land cover accuracy rarely obtains the commonly recommended 85% target. Its effect on climate simulations should therefore be considered, especially when historically reconstructed and future projected land covers are employed. Citation: Ge, J., J. Qi, B. M. Lofgren, N. Moore, N. Torbick, and J. M. Olson (2007), Impacts of land use/cover classification accuracy on regional climate simulations, J. Geophys. Res., 112, D05107, doi:. 1. Introduction [2] Human activities are transforming the surface of the Earth at an accelerated pace. Such disturbance of the land can affect local, regional, and global climate by changing the energy balance on the Earth's surface and the chemical composition of the atmosphere [Chase et al., 1999; Houghton et al., 1999; Pielke, 2001]. Over the past decades, land use/cover has been widely recognized as a critical factor mediating socioeconomic, political and cultural behavior and global climate change [International Geosphere- Biosphere Programme (IGBP), 1990; Lambin et al., 1999; Watson et al., 2000]. Numerous attempts have been made to understand past climate changes and to project potential future climate changes by incorporating reconstructed historical land cover changes and projected possible future land cover changes into numerical simulations [Xue, 1997; Pielke et al., 1999; Chase et al., 2000; DeFries et al., 2002; Taylor et al., 2002]. Recent studies have suggested that land use/cover change is a first-order climate effect at the global scale [Feddema et al., 2005]. [3] Until the last decade, land cover products used in most climate models were initially compiled from maps, ground surveys, and various national sources [Matthews, 1983; Olson et al., 1983], which have inherent limitations [Cihlar, 2000]. In the mid-1990s, global-scale land cover products generated from remote sensing images became available, and have been implemented into various land surface schemes [e.g., Dickinson et al., 1986; Sellers et al., 1986, 1996a, 1996b; Walko et al., 2000]. Recently, more land cover products at regional to global scales have been developed with enhanced qualities, such as Global Land Cover 2000 (GLC2000) and Moderate Resolution Imaging Spectroradiometer (MODIS) land cover [Mayaux et al., 2004; Friedl et al., 2002]. These products have great potential to be employed in numerical modeling systems in the near future. [4] However, no land cover data set is 100% accurate, even if developed from the most advanced satellite images. Other factors, such as the classification method, the sample size of evaluation data, and the inherent subjective characteristics of classification, can increase the uncertainties contained in land cover data sets. Such limitations have been recognized in the remote sensing community, and therefore quantitative accuracy assessment has been emphasized in most recent land cover classification research [Foody, 2002]. Some target accuracy thresholds have recently been recommended in an attempt to provide guide-