Population increases and environmental degradation are challenges for urban sustainability. Planning support systems are available to assist local authorities in developing strategies toward sustainability and resilience of urban areas, but are not always used in practice. We adapted an open-source planning support system to the case of Stockholm County, Sweden, where there is a productive working relationship between researchers, city planners, and regional planners. We employed a collaborative approach in extending and updating the planning support system and analyzed the outcomes, in order to both improve the planning support system and to investigate the process of planner engagement in planning support system development. The approach involved systematic interactions with local planning authorities and e.g. additional data processing, integrating scientific knowledge, policy, and engagement by planners in the complex process of planning for sustainable urban development. This made the planning support system more user-friendly for local planners, facilitating adoption by planning authorities through overcoming common quality and acceptance barriers to the use of planning support system in practice. Involving planners in planning support system development thus increases (i) planning support system quality, producing relevant and up-to-date outputs, and (ii) acceptance for planning support system by regional planners. Further assessment is required to determine whether planners can operate the adapted planning support system unaided.

Human-induced urban growth and sprawl have implications for greenhouse gas (GHG) emissions that may not be included in conventional GHG accounting methods. Improved understanding of this issue requires use of interactive, spatial-explicit social-ecological systems modeling. This paper develops a comprehensive approach to modeling GHG emissions from urban developments, considering Stockholm County, Sweden as a case study. GHG projections to 2040 with a social-ecological system model yield overall greater emissions than simple extrapolations in official climate action planning. The most pronounced difference in emissions (39% higher) from energy use single-residence buildings resulting from urban sprawl. And this difference is not accounted for in the simple extrapolations. Scenario results indicate that a zoning policy, restricting urban development in certain areas, can mitigate 72% of the total emission effects of the model-projected urban sprawl. The study outcomes include a decision support interface for communicating results and policy implications with policymakers.

Understanding interactions between complex human and natural systems involved in urban carbon cycling is important when balancing the dual goals of urban development to accommodate a growing population, while also achieving urban carbon neutrality. This study develops a systems breakdown accounting method to assess the urban carbon cycle. The method facilitates greater understanding of the complex interactions within and between systems involved in this cycle, in order to identify ways in which humans can adapt their interactions to reduce net greenhouse gas emissions from urban regions. Testing the systems breakdown accounting method in Stockholm County, Sweden, we find that it provides new insights into the carbon interactions with urban green-blue areas in the region. Results show how Stockholm County can reduce its emissions and achieve its goal of local carbon net-neutrality, if the green areas protect its carbon sequestration potential and maintain it to offset projected remaining active emissions. Results also show that the inland surface waters and inner archipelago waters within Stockholm County are a considerable source of greenhouse gases to the atmosphere. A better understanding of these water emissions is necessary to formulate effective planning and policy measures that can reduce urban emissions. The insights gained from this study can also be applied in other regions. In particular, water bodies could play a significant role in the urban carbon cycle and using this knowledge for more complete carbon accounting, and a better understanding of green-blue interactions could help to reduce net urban emissions in many places.

We assessed the mitigation potential of nature-based solutions (NbS) within commonly overlooked pathways, including human behavioral interventions and resource savings, in addition to the well-understood carbon sequestration area. We found that general NbS implementation in the residential, transport, and industrial sectors of European cities can reduce urban carbon emissions by up to 25%. Based on spatial patterns of carbon emissions and the local context of each city, we then prioritized spatial allocation of different types of NbS implementations within 54 major EU cities, in order to maximize the carbon emissions reduction potential. We found that prioritized NbS could reduce human activity-related carbon emissions by on average 17.4% for all cities, with 8.1%, 14.0%, and 9.6% reduction in the residential, industrial, and transport sector, respectively, while 5.6% of the remaining carbon emissions could be captured by carbon sequestration. Projections to 2030 showed that prioritized NbS implementations on all available land parcels in the RCP 1.9 scenario would reduce total carbon emissions by on average 62.5% (95% CI: 47.9–66.7%) compared with the baseline scenario, with NbS capturing 22.0% marginal emissions and sequestration capturing 13.3%. Some pioneering cities climate action are projected to be very close to achieve carbon neutrality by 2030 while 3 cities can realize the goal. For carbon neutrality, cities therefore need to co-integrate indirect (human behaviors and resource saving) and direct (sequestration) contributions of NbS into aggressive climate action plans.