The Importance of Integrating Green and Gray Infrastructure
The anticipated increase in urban population of 2.5 billion people by 2050 poses significant environmental challenges. While the various environmental impacts of urbanization have been studied individually, integrated approaches are rare. This study introduces a spatially explicit model to assess urbanization’s effects on ecosystem services (green infrastructure availability, cooling, stormwater retention) and the environmental impact of building construction (material demand, greenhouse gas emissions, land use).
Applied to the Netherlands from 2018 to 2050, our results show that integrating green infrastructure development with building construction could increase green areas by up to 5% and stabilize or increase ecosystem service provisioning. Dense building construction with green infrastructure development is generally more beneficial across the Netherlands, reducing resource use and enhancing ecosystem services. Conversely, sparse construction with green infrastructure is more advantageous for newly built areas. These findings offer insights into the environmental consequences of urbanization, guiding sustainable urban planning practices.
Assessing the Global and Local Impacts of Urbanization
Our analysis begins with spatially explicit strategies for building construction and demolition from 2018 to 2050, as outlined by the Dutch Environmental Assessment Agency. We focus primarily on two contrasting approaches: the Dense strategy, which concentrates construction within present urban areas, and the Sparse strategy, which promotes development in low-density areas such as agricultural and industrial sites.
We first analyze the effects of urbanization on the non-local aspects: the demand for primary building materials, the greenhouse gas emissions, and the embodied land use associated with the extraction and production of construction materials. Our approach incorporates three construction methods: conventional, circular, and biobased. These methods are applied within the frameworks of the Dense and Sparse urbanization strategies.
Secondly, we assess how these urbanization strategies affect local land use change and its impacts on local ecosystem service supply: local green infrastructure availability, air temperature regulation, and stormwater retention capacity. We integrate the Dense and Sparse strategies with two distinct land-use approaches: Green, emphasizing extensive greening around buildings, and Gray, characterized by minimal green infrastructure development.
In the final step, we identify the most effective combination of building and land-use strategies for each sustainability indicator, highlighting key synergies and trade-offs.
Impacts on Building Materials and Construction
The global warming potential associated with building materials totals between 68 and 127 megaton (Mt) CO2-equivalent in the period 2018-2050, dependent on the urbanization strategy and choice of building materials. Annually, this can be translated into an average of 2-4 Mt/year, relatively low compared to the impact related to space heating, which encompassed 24.7 Mt CO2-equivalent in 2018 alone.
Biobased construction stands out with the lowest demand for primary materials and the lowest embodied greenhouse gas emissions, largely as a result of replacing concrete structures with wooden ones. However, biobased construction exhibits a notably high embodied land use impact related to wood production, reaching over 16000 km2 for strategy Sparse and Biobased, equivalent to 40% of the Netherlands’ surface area. Overall, the circular construction appears to be the most favorable choice, resulting in lower primary material use as well as lower CO2-emissions, without the trade-off to embodied land use.
From a building material perspective, prioritizing denser building practices over sparse ones is the more sustainable choice. While densification leads to increased building replacements, consequently raising the demand for materials, the structures created in denser environments are generally smaller, favoring multi-family dwellings over single-family houses. Together with the greater potential for secondary material use, this results in a reduced environmental impact compared to sparse building construction.
Impacts on Ecosystem Services
Our findings show that buildings present a relatively small portion of the total transformed land area and therefore highlight the potential for concurrent growth in green infrastructure alongside the expansion of building area for strategy Green. Among the strategies considered, the Sparse-Green combination emerges as the most effective in expanding the area of green infrastructure, with an increase of 5% compared to 2018 (3% for Dense-Green). The higher value for Sparse stems from a lower building density, resulting in a larger area of transformed land.
The choice of the most effective urbanization strategy for urban cooling varies depending on the scale of analysis. Focusing on newly constructed areas between 2018 and 2050, the Sparse-Green approach is the preferred strategy, slightly reducing air temperature by 0.4%, corresponding to 0.12 oC on hot summer days. In contrast, the Dense-Green strategy results in a small increase of 0.5%. However, when analyzing the entire building stock, the Dense strategy emerges as more effective, showing a marginal decrease in air temperature by 0.01%.
In the context of stormwater retention, our analysis reveals that dense urban construction, when integrated with green infrastructure, exhibits a slightly higher retention capacity compared to sparse building constructions. The Dense-Green strategy shows more than 20% increase in stormwater retention for new constructions, compared to an slightly less than 20% increase observed under the Sparse-Green strategy.
Balancing Trade-offs and Optimizing Sustainability
Our findings reveal trade-offs between dense and sparse urban development in terms of environmental impact and the provision of ecosystem services, underscoring their importance in determining sustainable urban development strategies. While dense urban development is preferred from a building material perspective, green infrastructure development in densely populated areas could pose challenges due to high demand for services associated with gray infrastructure.
Sparse building construction, on the other hand, primarily results in a trade-off between agricultural land and built-up areas. In the Netherlands, where natural areas are scarce, sparse urban development could positively impact ecosystem service provisioning and biodiversity when coupled with the development of green infrastructure. However, to sustain food production, sparse urban development could inadvertently lead to the transformation of other areas rich in biodiversity into agricultural land.
Integrating green infrastructure with new building construction is not enough to achieve substantial cooling, suggesting that additional greening measures are required, either through the integration of green infrastructure in buildings or through reducing building densities. Across the assessed building strategies, the biobased strategy showed the lowest greenhouse gas emissions but significantly impacted embodied land use due to the requirements for wood cultivation.
Overall, the circular building strategy results in the least trade-offs, as it facilitates material recycling and component reuse, making it an attractive option for the long-term sustainability of the built environment. The feasibility of implementing our method in other areas, especially in rapidly urbanizing regions like the Global South, is contingent upon data availability, but open-source land-cover data and LULC change models can provide a potential foundation for analyzing sustainable urbanization strategies across diverse global contexts.
Conclusion: Towards Integrated and Sustainable Urban Development
Our study offers an in-depth analysis of the environmental impacts of urban development, emphasizing the integration of green and gray infrastructure and how they affect building construction related impacts and ecosystem services. Despite the projected growth of the Dutch building stock, our study illustrates the possibility of simultaneously expanding green infrastructure by up to 5% and maintaining or improving the supply of ecosystem services compared to 2018 levels.
The analysis reveals trade-offs between dense and sparse urban development in terms of environmental impact and the provision of ecosystem services, underscoring their importance in determining sustainable urban development strategies. Lessons from this research can be adapted to other urban environments to enhance their understanding and implementation of sustainable urban development approaches, aligning with broader international commitments to address climate change and foster sustainable cities.
