Overview
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Urban expansion changes land–atmosphere interactions. This project used CESM’s Community Land Model (CLM5) to test how
increasing the fraction of urban land impacts surface energy fluxes and temperatures. I modified the prescribed land
surface dataset (
fsurdat) to increase urban fraction by +10% and +50% across the Eastern U.S. and compared against a control run.
Approach
- Ran land-only CLM5 simulations (f09_g17 resolution) for 10 years.
- Increased urban fraction (PCT_URBAN) by +10% and +50%, balanced by decreasing vegetation (PCT_NATVEG).
- Examined changes in sensible heat flux (FSH), ground temperature (TG), 2 m air temperature (TSA), and internal building air temperature (TBUILD).
Figure 2:a) PCT_URBAN in default fsurdat file over eastern US before any changes, b) PCT_urban after +50% changes and c)
difference between before and after changes, d) PCT_NATVEG in default fsurdat file over eastern US before any changes, e)
PCT_NATVEG after decreasing by the same amount the PCT_URBAN increased per grid cell, f) difference in PCT_NATVEG
before and after
Key Findings
- Sensible Heat Flux: Increased by up to +3 W/m² in some regions.
- Surface & Air Temps: Small but detectable changes (<0.5 K) in ground, 2 m air, and building air temperatures.
- Regional Sensitivity: Strongest signals appeared over South Asia/Tibetan Plateau due to unintended masking—showing model sensitivity.
- Scale of Change: 10% urban increase showed little effect, while +50% revealed meaningful signals.
Implications
Even modest increases in urban land cover can alter surface energy fluxes. Results highlight the need for improved representation of urban processes in Earth system models. Future work should apply changes over intended regions, test fully coupled simulations, and investigate compounded urban–climate risks.