Representing dynamic urban land change in the Community Earth System Model (CESM)

Urbanization (urban land change) alters local and regional climate through biophysical and biogeochemical processes and has broader climate impacts through atmospheric feedbacks. Despite its critical climate impacts, urban areas have rarely been explicitly represented in global-scale Earth system models, and physically-based transient urban representations are missing as well. The Community Earth System Model (CESM) has a physically based urban land parameterization – Community Land Model Urban (CLMU) – that is sufficiently detailed to represent the properties and processes in the urban environment. We improve this model by implementing a dynamic urban scheme to represent transient land use due to urbanization. Leveraging existing urbanization projection datasets, the new scheme allows urban extent to be updated annually during a climate simulation while conserving energy and mass balance during the transition. Land-only simulation results confirm the robustness of the new dynamic urban scheme and demonstrate the direct local climate effects induced by urban land expansion. In the appendix of this paper, we also document two recent improvements to the building energy scheme of CLMU.