Abstract
The urban population is predicted to reach a 70% share of global population by mid-century. Future urbanization might be directed along several development typologies, e.g. sprawling urbanization, more compact cities, greener cities, or a combination of different typologies. These developments induce urban land-use change that will affect urban climate and might reinforce phenomena such as the urban heat island and thermal discomfort of urban residents. A planning-based mitigation approach to ensure thermal comfort of residents are urban cold-air paths, i.e. low-roughness areas enabling drainage and transport of colder air masses from rural surroundings. We study how urban land-use change scenarios influence cold-air path occurrence probability and spatial distribution in a mid-European city using a machine learning approach, i.e. boosted regression trees. The Urban Sprawl Scenario results in the strongest reduction of cold-air path area by 3.6% in comparison to the reference case. The Green City Scenario gives evidence for an increase of cold-air path area (2.2%) whereas the Compact Green City Scenario partly counteracts the negative influence of urban densification by increased fractions of vegetated areas. The proposed method allows for the identification of priority areas for cold-air path preservation in urban planning.
Highlights
Global urbanization is projected to further increase the urban population by about 1.2 billion people by 2030 with a likely expansion of urban land area by 1.2–1.8 million km2 between 2000 and 2030 (McDonald et al, 2020; Seto and Pandey, 2019)
– compact green cities, which are a combination of compact city and green city development (Artmann et al, 2019; Richter and Behnisch, 2019)
This makes Braunschweig a good test-case to investigate to which extent land-use change by urban development affects cold-air path occurrence
Summary
Global urbanization is projected to further increase the urban population by about 1.2 billion people by 2030 with a likely expansion of urban land area by 1.2–1.8 million km between 2000 and 2030 (McDonald et al, 2020; Seto and Pandey, 2019). Despite the urbanization process on a global scale, a city is constantly developing and transforming on the local scale (Mahtta et al, 2019; Tonne et al, 2021) These processes might be triggered by economic prosperity or economic decline, a growing or shrinking urban population and by different municipal planning concepts, e.g. more sustainable urban design. Urban development results in changes of land-use mainly with conversion of natural surfaces into artificial surface types These processes modify the urban atmosphere and might reinforce phenomena such as the urban heat island (UHI, Huang et al, 2019; JatoEspino, 2019; Manoli et al, 2019) which is projected to intensify with global warming due to more frequent heat waves and hot summer nights Higher urban temperatures will increase the bioclimatic burden and mortality of the urban population (e.g. Li et al, 2012; Gabriel and Endlicher, 2011)
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