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Subject: urban area × WGL Institute: PIK ×

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    On the influence of density and morphology on the Urban Heat Island intensity
    ([London] : Nature Publishing Group UK, 2020) Li, Yunfei; Schubert, Sebastian; Kropp, Jürgen P.; Rybski, Diego
    The canopy layer urban heat island (UHI) effect, as manifested by elevated near-surface air temperatures in urban areas, exposes urban dwellers to additional heat stress in many cities, specially during heat waves. We simulate the urban climate of various generated cities under the same weather conditions. For mono-centric cities, we propose a linear combination of logarithmic city area and logarithmic gross building volume, which also captures the influence of building density. By studying various city shapes, we generalise and propose a reduced form to estimate UHI intensities based only on the structure of urban sites, as well as their relative distances. We conclude that in addition to the size, the UHI intensity of a city is directly related to the density and an amplifying effect that urban sites have on each other. Our approach can serve as a UHI rule of thumb for the comparison of urban development scenarios.
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    Physical and virtual carbon metabolism of global cities
    ([London] : Nature Publishing Group UK, 2020) Chen, Shaoqing; Chen, Bin; Feng, Kuishuang; Liu, Zhu; Fromer, Neil; Tan, Xianchun; Alsaedi, Ahmed; Hayat, Tasawar; Weisz, Helga; Schellnhuber, Hans Joachim; Hubacek, Klaus
    Urban activities have profound and lasting effects on the global carbon balance. Here we develop a consistent metabolic approach that combines two complementary carbon accounts, the physical carbon balance and the fossil fuel-derived gaseous carbon footprint, to track carbon coming into, being added to urban stocks, and eventually leaving the city. We find that over 88% of the physical carbon in 16 global cities is imported from outside their urban boundaries, and this outsourcing of carbon is notably amplified by virtual emissions from upstream activities that contribute 33–68% to their total carbon inflows. While 13–33% of the carbon appropriated by cities is immediately combusted and released as CO2, between 8 and 24% is stored in durable household goods or becomes part of other urban stocks. Inventorying carbon consumed and stored for urban metabolism should be given more credit for the role it can play in stabilizing future global climate.