## 1 Introduction  
As development becomes more extensive, planning land use and land cover (LULC) of urban areas is increasingly important, in part because urbanization has been associated with reduced carbon sequestration [1; 2]. On a global scale, the area available for land use and land cover change (LULCC) within urban areas is relatively small, so it has a minor effect on greenhouse gas (GHG) dynamics. However, in areas in which the LULCC exceeds 10%, there has been a noticeable change in carbon emissions [1]. Realistically, there is a limited amount of land within cities that can be converted to other land use types. In this study, biogeochemical modeling is used to evaluate the effect of LULCC on carbon and water dynamics in Lehigh Valley, Pennsylvania, USA, relative to climate policy initiatives. Lehigh Valley consists of Lehigh and Northampton counties, and this study also considers a focus on the city of Bethlehem. The city of Bethlehem has developed a climate action plan [3] that outlines the specific LULCC the city plans to implement to reach zero carbon emissions by 2040. To test the effectiveness of these policies, sensitivity experiments were developed for 2020-2099 to determine the type and magnitude of urban land use change needed to meet these goals. The terrestrial ecosystem model (TEM) is a biogeochemical model of terrestrial ecosystems that tracks the flow of carbon, nitrogen, and water among the atmosphere, vegetation, and soils. The model has been used to study the effect of human disturbances like LULCC, climate change, elevated CO2, ozone, and nitrogen deposition on carbon sequestration and ecosystem services [4; 5; 6; 7; 8]. By inputting LULC and climate data for Lehigh Valley into the model, information about carbon fluxes, as well as moisture dynamics, can be determined. Changing the number of land use types (impervious, barren, deciduous and confiferousforests, lawn, cropland, and pastureland) and running these different regimes in TEM allows changes in water and carbon storage associated with different potential land use policies to be estimated. When considering carbon dynamics and LULC, it is well documented that urban areas have low primary productivity and thus carbon storage [9]. Ecosystems such as fertilized cropland, forests, and grazing pastures are among the highest carbon sinks [10]. Urban turf lawns are fertilized and therefore can also be strong carbon sinks [11]. Growing new shrubs and trees will be a net carbon sink, and over time, the sink may continue due to future disturbance and regrowth or growth enhancements from nitrogen deposition and elevated atmospheric CO\({}_{2}\)[12; 13]. However, in accounting for the entire carbon history, moving and decomposition more than offset enhanced growth from fertilizers [10]. One measure of carbon sequestration by the land that accounts for the effects of disturbance and land management is net carbon exchange (NCE), which is net ecosystem productivity (NEP) minus the fluxes associated with land conversion and product decomposition [10]. A more positive NCE is indicative of a stronger carbon sink. When considering the impact of urbanization on carbon dynamics, soils are often not considered. In areas that have a low soil organic carbon (SOC), such as the warm and dry Midwest and the western United States, urbanization results in a gain in SOC [14]. For areas that have a higher SOC, such as the colder northeastern United States, urbanization decreases SOC [14]. Of the cities listed in this study, Bethlehem is most similar to Baltimore, which saw a 2.2% decrease in SOC. Increasing urbanization and the replacement of forests or turf lawns with impervious surfaces also increase the amount of water runoff within these areas. Carbon sequestration is currently not accounted for in the city's GHG inventory.