@article{FluschnikKriewaldRosetal.2016,
  author    = {Fluschnik, Till and Kriewald, Steffen and Ros, Anselmo Garcia Cantu and Zhou, Bin and Reusser, Dominik Edwin and Kropp, J{\"u}rgen and Rybski, Diego},
  title     = {The Size Distribution, Scaling Properties and Spatial Organization of Urban Clusters: A Global and Regional Percolation Perspective},
  series = {ISPRS International Journal of Geo-Information},
  volume    = {5},
  journal   = {ISPRS International Journal of Geo-Information},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {2220-9964},
  doi       = {10.3390/ijgi5070110},
  pages     = {1543 -- 1559},
  year      = {2016},
  abstract  = {Human development has far-reaching impacts on the surface of the globe. The transformation of natural land cover occurs in different forms, and urban growth is one of the most eminent transformative processes. We analyze global land cover data and extract cities as defined by maximally connected urban clusters. The analysis of the city size distribution for all cities on the globe confirms Zipf's law. Moreover, by investigating the percolation properties of the clustering of urban areas we assess the closeness to criticality for various countries. At the critical thresholds, the urban land cover of the countries undergoes a transition from separated clusters to a gigantic component on the country scale. We study the Zipf-exponents as a function of the closeness to percolation and find a systematic dependence, which could be the reason for deviating exponents reported in the literature. Moreover, we investigate the average size of the clusters as a function of the proximity to percolation and find country specific behavior. By relating the standard deviation and the average of cluster sizes—analogous to Taylor's law—we suggest an alternative way to identify the percolation transition. We calculate spatial correlations of the urban land cover and find long-range correlations. Finally, by relating the areas of cities with population figures we address the global aspect of the allometry of cities, finding an exponent \&\#948; \&\#8776; 0.85, i.e., large cities have lower densities.},
  language  = {en}
}
@article{GudipudiFluschnikRosetal.2016,
  author    = {Gudipudi, Venkata Ramana and Fluschnik, Till and Ros, Anselmo Garcia Cantu and Walther, Carsten and Kropp, J{\"u}rgen},
  title     = {City density and CO2 efficiency},
  series = {Energy policy : the international journal of the political, economic, planning, environmental and social aspects of energy},
  volume    = {91},
  journal   = {Energy policy : the international journal of the political, economic, planning, environmental and social aspects of energy},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {0301-4215},
  doi       = {10.1016/j.enpol.2016.01.015},
  pages     = {352 -- 361},
  year      = {2016},
  abstract  = {Cities play a vital role in the global climate change mitigation agenda. City population density is one of the key factors that influence urban energy consumption and the subsequent GHG emissions. However, previous research on the relationship between population density and GHG emissions led to contradictory results due to urban/rural definition conundrum and the varying methodologies for estimating GHG emissions. This work addresses these ambiguities by employing the City Clustering Algorithm (CCA) and utilizing the gridded CO2 emissions data. Our results, derived from the analysis of all inhabited areas in the US, show a sub-linear relationship between population density and the total emissions (i.e. the sum of on-road and building emissions) on a per capita basis. Accordingly, we find that doubling the population density would entail a reduction in the total CO2 emissions in buildings and on-road sectors typically by at least 42\%. Moreover, we find that population density exerts a higher influence on on-road emissions than buildings emissions. From an energy consumption point of view, our results suggest that on-going urban sprawl will lead to an increase in on-road energy consumption in cities and therefore stresses the importance of developing adequate local policy measures to limit urban sprawl. (C) 2016 Elsevier Ltd. All rights reserved.},
  language  = {en}
}