Carolina Environmental Program
Enst94
The Stella Model for Carbon Emissions
 
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    A model of carbon flows within Chapel Hill was created using a computer program called STELLA.  This model is a modified version of a global module that can be downloaded at http://www.unc.edu/%7Edcrawfor/globwarm.stm.  A full explanation of the model can be found at http://www.unc.edu/%7Edcrawfor/glowarm.htm.

    The above image is a visual representation of the interaction of the different compartments included in the STELLA model.  Carbon emissions originate toward the outer edge of the model, and different environmental and physical interactions eventually deposit virtually all of the carbon in four locations: mixing ocean, soil/litter, flora, and the atmosphere.  The mixing ocean, soil/litter, and flora are all considered carbon sinks, sequestering carbon from the atmosphere.  Deep earth interactions, including volcanic activity, contribute carbon to the environment.  And finally, the compartment for atmospheric carbon is the location for our final number.  This is the compartment whose value we aim to reduce to a doubling of the pre-industrial levels in Earth's atmosphere.

    The initial amount of carbon in each compartment (i.e. atmosphere) was adjusted to represent the amount within Chapel Hill.  In order to do so, the global values were multiplied by the ratio of land area in Chapel Hill to the total land area for the entire globe.  This assumption implies homogenous distribution of carbon within each compartment.

    Land use data was aggregated.  The Net Primary Productivity (NPP) for Chapel Hill could not be found.  In addition, the area of Chapel Hill could not be split up by land type.  Thus the total land area of Chapel Hill was used.  A value for the average NPP for the entire state of North Carolina was found (Chaves, 2004) and assumed to be relevant to Chapel Hill.

    Data on the population of Chapel Hill was taken from the Chapel Hill Chamber of Commerce.  At the current rate of growth, 0.021, the population in Chapel Hill would expand exponentially.  A factor, kbr, was included.  This factor causes the population to stabilize.  As the value of kbr approaches 1, the population stabilizes more quickly.  As will be noted in graphical displays, the Chapel Hill immigration rate has a dramatic effect on carbon emission rates as it pertains to population growth.  This parameter will be considered and dealt with later.

    The major sectors consuming energy in Chapel Hill are Commercial, Residential, and Transportation.  The Industrial sector was assumed to have no effect and was left out of the model.  Data obtained from Duke Energy was used to arrive at relevant values for the amount of energy consumed in the commercial and residential sectors (i.e. fraction of energy supplied by each source and total demand).  Transportation data was obtained from Jeremy Raw, the Transportation Systems Engineer of the City of Durham.

    A summary of all STELLA model parameters and any deviations from the global model parameters can be found in this table.  Our emissions modeling, along with our proposed changes can be found here.
 
 

This site designed by Joey Hester
Last Update: May 3, 2005
Project Designed and Executed by:
Karen Kaufman, Bobby O'Connor, Sarah Clark, Maceik Krzysztoforski, Joey Hester