Impact of urbanization on US surface climate

We combine Landsat and MODIS data in a land model to assess the impact of urbanization on US surface climate. For cities built within forests, daytime urban land surface temperature (LST) is much higher than that of vegetated lands. For example, in Washington DC and Atlanta, daytime mean temperature differences between impervious and vegetated lands reach 3.3 and 2.0 degrees C, respectively. Conversely, for cities built within arid lands, such as Phoenix, urban areas are 2.2 degrees C cooler than surrounding shrubs. We find that the choice and amount of tree species in urban settings play a commanding role in modulating cities' LST. At continental and monthly scales, impervious surfaces are 1.9 degrees C +/- 0.6 degrees C warmer than surroundings during summer and expel 12% of incoming precipitation as surface runoff compared to 3.2% over vegetation. We also show that the carbon lost to urbanization represents 1.8% of the continental total, a striking number considering urbanization occupies only 1.1% of the US land. With a small areal extent, urbanization has significant effects on surface energy, water and carbon budgets and reveals an uneven impact on surface climate that should inform upon policy options for improving urban growth including heat mitigation and carbon sequestration.