Reitemeyer Fabian, Ribeiro Fabiano L, Schwarz Jan, Gugel Benjamin, Schacht Alexander, Rybski Diego
District Office Friedrichshain-Kreuzberg, Organizational Unit Climate and International, Berlin, Germany.
University of Potsdam, Institute of Environmental Science and Geography, Potsdam, Germany.
PLoS One. 2025 Sep 3;20(9):e0330079. doi: 10.1371/journal.pone.0330079. eCollection 2025.
Cities exhibit both beneficial and detrimental characteristics, many of which stem from agglomeration effects and are, to a first approximation, influenced by population size. However, urban density also plays a critical role. For example, cities with similar population sizes but higher densities tend to emit less carbon, while simultaneously exhibiting a more pronounced urban heat island (UHI) effect. This trade-off highlights the need for a balanced approach that simultaneously minimizes both carbon emissions and the urban heat island (UHI) effect. To address this challenge, we examine how both carbon emissions and UHI intensity are influenced by the population size and spatial extent of the cities. As objective function we define the some of both quantities where city population and area are variables. Considering the scaling relation between area and population as constraint, we derive a theoretical expression leading to an optimal city size. To validate our approach, we analyze carbon emissions data from cities in Germany and consider UHI parameters from the literature. We find that, in the specific case of German cities, achieving an optimal city size that simultaneously minimizes both carbon emissions and UHI intensity is not physically feasible. From a methodological perspective, only the UHI intensity parameters, together with the exponent of the relationship between population and area, determine whether an optimum exists or not. We argue that instead, the scaling relation between population and area itself should be understood as an optimum.
城市呈现出有益和有害的特征，其中许多源于集聚效应，并且在一阶近似下，受人口规模影响。然而，城市密度也起着关键作用。例如，人口规模相似但密度较高的城市往往碳排放较少，同时呈现出更明显的城市热岛（UHI）效应。这种权衡凸显了需要一种平衡的方法，同时将碳排放和城市热岛（UHI）效应降至最低。为应对这一挑战，我们研究了碳排放和UHI强度如何受到城市人口规模和空间范围的影响。作为目标函数，我们定义了这两个量的总和，其中城市人口和面积是变量。考虑到面积和人口之间的比例关系作为约束条件，我们推导出一个理论表达式，得出最优城市规模。为验证我们的方法，我们分析了德国城市的碳排放数据，并考虑了文献中的UHI参数。我们发现，在德国城市的特定情况下，实现一个能同时将碳排放和UHI强度降至最低的最优城市规模在实际中是不可行的。从方法论的角度来看，只有UHI强度参数以及人口与面积关系的指数决定是否存在最优解。我们认为，相反，人口与面积本身的比例关系应被理解为一种最优解。
