This study aimed to analyze the improvement in outdoor thermal environment by greening of persistently vacant housing and open areas in a densely built old downtown area of Busan Metropolitan City using ENVI-met. Simulation was performed for a summer day by constructing four scenarios for four areas considering the building density and slope direction. The results indicate that compared to the current scenario, the concrete scenario had the worst thermal environment, where the average temperature, mean radiant temperature (MRT), and physiological equivalent temperature (PET) increased by 0.04°C, 1.49°C, and 0.51°C, respectively. In contrast, the tree scenario exhibited the most significant improvement. The average temperature, MRT, and PET decreased by 0.03°C, 1.66°C, and 0.65°C, respectively. Moreover, the removal of vacant houses in dense residential areas improved ventilation, and PET decreased by approximately 8°C locally. Planting trees higher than the demolished vacant houses mitigated the thermal environment considerably. The effect of greening was the strongest in the residential areas located on the south-facing slope with the worst thermal environment. This study provides essential data for implementing greening as a smart reduction strategy in the sustainable management of vacant houses.

This study aims to evaluate the climate-change response of greening persistently vacant houses and barren sites in deteriorated high-density residential areas in old downtown metropolitan areas. The current status of building demolition sites in Ami-dong and Chojang-dong, Busan Metropolitan City, was examined. In this area, of the 340 vacant houses from 2017, 246 (72.35%) remained persistently vacant till 2020. In 2020, 213 barren sites were neglected after building demolition. Amongst these sites, 177 (83.10%) were paved with concrete. Persistently vacant houses and barren sites were afforested, and the climate-change response was quantified in terms of flood reduction and CO2 mitigation in four scenarios (current, concrete, ground cover plants, and trees). Runoff analysis was performed using the Korea low-impact development model (K-LIDM) to assess flood mitigation. The tree scenario showed average runoff mitigations of 1.71%, 2.38%, and 3.06% in the long-term, 30-year, and 2-year rainfall scenarios, respectively. Additionally, 3058 deciduous broadleaf trees may be planted in the study area to promote CO2 mitigation. Thus, an additional annual carbon fixation of 62,123.78 kg CO2 may be expected. The greening of vacant houses and demolished sites was effective in all aspects of the climate-change response, and tree-based greening exhibited the most significant effect.

While greening vacant houses is encouraged as a sustainable strategy, there is a paucity of quantitative research on its effects. The purpose of this study is to evaluate the flood risk and CO₂ mitigation effects of greening neglected vacant houses and barren sites in densely built old downtown areas. To achieve this goal, an investigation was conducted of the actual conditions of vacant houses and barren sites in Ami-dong and Chojang-dong in Busan Metropolitan City. Subsequently, four scenarios for greening vacant houses and barren sites were developed, and rainfall runoff simulations were performed using the K-LIDM model. Furthermore, the annual CO₂ fixation for greening with trees was calculated using established research formulas. This study found that 73% of vacant houses in the study area remain unoccupied for an extended period, and when demolished, 56% become concrete-paved barren sites. The runoff simulations indicated that greening with trees led to a 1.71% decrease in annual runoff volume in the long-term model, with peak runoff volume reductions of 3.06% and 2.38% during 2-year and 30-year rainfall events in the short-term model, respectively. Planting trees could accommodate 3058 trees, fixing 62,124 kg of CO₂ annually. This study demonstrates the climate change response effects of greening vacant houses.