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J. S. Kimball, K. C. McDonald, and M. Zhao

production (NPP) is the primary conduit of carbon transfer from the atmosphere to the land surface and is thus a fundamental component of the global carbon cycle. In seasonally frozen environments, vegetation productivity is constrained by low temperatures and plant-available moisture for much of the year, while the active growing season is primarily determined by length of the nonfrozen period ( Jarvis and Linder 2000 ; Kimball et al. 2004 ). Boreal forest and arctic tundra biomes of the northern high

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M. A. Rawlins, S. Frolking, R. B. Lammers, and C. J. Vörösmarty

in section 2.4 . 2.2. Model description We use the Pan-Arctic Water Balance Model (PWBM; Rawlins et al. 2003 ) to simulate runoff and ET at an implicit daily time step across the WALE domain. This hydrological model uses gridded fields of plant rooting depth, soil characteristics (texture, organic content), and vegetation and is driven with daily time series of precipitation and air temperature. The PWBM incorporates a soil organic layer and a soil moisture phase-change submodel that partitions

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J. S. Kimball, M. Zhao, A. D. McGuire, F. A. Heinsch, J. Clein, M. Calef, W. M. Jolly, S. Kang, S. E. Euskirchen, K. C. McDonald, and S. W. Running

calculated for both evergreen and deciduous vegetation from an empirical phenology model and deviations of current air temperature, soil moisture, and incident solar radiation conditions from the long-term climatology of the site ( White et al. 1997 ; Thornton et al. 2002 ). Atmospheric N deposition occurs at a constant daily rate applied directly to a soil mineral N pool; N leaching and removal from the system occurs as a constant fraction of soil water outflow. Whole-plant mortality is calculated, in

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Joy Clein, A. David McGuire, Eugenie S. Euskirchen, and Monika Calef

temperature, rs is the instantaneous rate of change in decomposition with the change in temperature, and f  ( M ) is a scalar between 0 and 1 of volumetric soil moisture ( M ) effects on decomposition. The per-gram-biomass respiration rate of the soil is affected by the nitrogen concentration of litter that enters the soil. The change in vegetation carbon is calculated as the difference between NPP and the litterfall flux of carbon ( L c ), while the change in soil carbon is calculated as the difference

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T. Scott Rupp, Xi Chen, Mark Olson, and A. David McGuire

number generator and as a function of the flammability value of that pixel ( Rupp et al. 2000b ; Rupp et al. 2002 ). The flammability value of each pixel is a function of vegetation type and age (i.e., fuel loading/structure) and growing-season climate (i.e., fuel moisture). Therefore, random ignitions will be concentrated in pixels with the highest fuel loads and experiencing the driest climate conditions for any given time step. For this research we simulated only lightning ignitions. Human

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Wanli Wu, Amanda H. Lynch, Sheldon Drobot, James Maslanik, A. David McGuire, and Ute Herzfeld

Arctic environmental system and interactions among different components, especially in the face of potential climatic change. However, consistent observations of components of the terrestrial water budget are routinely unavailable. While some terms of the surface water balance are reasonably well observed [precipitation (PRC) and runoff in particular], other terms including evapotranspiration and soil moisture are generally not directly observed. Many of these variables are difficult to measure

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