As urbanization in China progresses, urban spatial development is transitioning from rapid expansion to more intensive and compact growth. This study examined the role of physical geography and environmental factors in shaping the urban spatial development in the Guangdong-Hong Kong-Macao Greater Bay Area (GBA). Based on the current natural conditions, we selected evaluation indices from topography, hydrogeology, climatic conditions, and natural disasters. These indices were used to create a carrying capacity and suitability evaluation system for development land under natural constraints. Finally, the spatial development potential of the city was finalized by taking into account the current state of the built-up area of the city. Meanwhile, we employed the Optimal Parameters-based Geographical Detector and assessed the impact of 14 natural factors on the spatial development of urban built-up areas. In 2020, the GBA had 52,168.77 km² of land suitable for construction, of which 34,241.13 km² was highly suitable (61.29%) and 17,927.64 km² was moderately suitable (32.09%). At the Bay Area level, 90.15% of the development potential remains untapped; at the city level, Zhaoqing City has the highest potential at 99.56%, while Macao has the lowest at 26.83%. Key factors influencing urban development include silty sand content, annual average relative humidity, and cumulative temperature above 0 °C, with varying impacts across different urban scales. At the Bay Area level, the silty sand content, annual average relative humidity, and cumulative temperature above 0 °C are the main influencing factors on the spatial development of urban built-up areas; at the city level, the main factors are annual average relative humidity and cumulative active temperature above 0 °C. This study reveals the important influence of natural environmental factors on urban spatial development, which is conducive to promoting sustainable development of land resources in GBA.

Against the backdrop of rapid population aging and significant demographic changes, cities are facing great challenges in providing healthcare resources for the elderly. Understanding the equity and spatial differentiation mechanisms between the demand and supply of healthcare resources for the elderly in cities, especially in rapidly urbanized areas, can help policymakers to promote the planning and construction of a ‘Just City’ and ‘Age-Friendly City’, safeguarding the human well-being of the elderly. This study combines outpatient appointment data classified by service type with community-scale demographic data to assess the equity in the supply of medical resources for the elderly in the city using a refined two-step moving search method. Taking Xiamen City as an example, we analyzed the spatial heterogeneity in the equity in the supply of different types of health care services for potential elderly patients in each community in the city. Then, we selected six driving factors to explore the underlying driving factors. The results showed that there were 308 communities (61.11%) with a high medical service balance of the internal medicine type for the elderly in Xiamen City, concentrated in the southwest of the whole area. There are only 157 communities with high medical service balance for the surgical type of medical services, concentrated in the central part and southwest of Xiamen City. For these two types of medical services, the number of communities with low medical service balance is 30 (5.95%) and 182 (36.11%), respectively. These communities are far away from the central city. Economic vitality is the most important driving factor in the spatial distribution pattern of equity in the balance of medical services for the elderly. Our study can provide quantitative information on the current situation evaluation and decision support for the development and design of a ‘Just City’ and ‘Age-Friendly City’ Planning.

Due to climate change and urbanization, green roofs are vital for urban climate resilience. However, there is currently no consensus on the photosynthetic carbon uptake capacity of green roof plants in cities. This study investigated and compared nine common green roof plant species in Xiamen, a typical coastal city in southeastern China. Their photosynthetic parameters were measured across all four seasons to evaluate photosynthetic carbon uptake capacity, and the differences among the nine plant species were evaluated. Results show: (1) Significant interspecific differences exist. Ligustrum japonicum (Lj) had the highest seasonal average daily carbon uptake per unit leaf area (8.86 g m⁻² d⁻¹) and per unit area (93.10 g m⁻² d⁻¹), approximately 9 times that of the lowest-performing species per unit leaf area (Pedilanthus tithymaloides) and 11 times that of the lowest-performing species per unit area (Tradescantia spathacea). (2) The variation in carbon uptake capacity among different green roof plant species followed a pattern consistent with that of their net photosynthetic rate and leaf area index. (3) Overall, the carbon uptake capacity of the nine plant species exhibited a trend of trees > shrubs > herbs. In summary, Lj demonstrated the highest photosynthetic carbon uptake capacity among the nine species examined, suggesting its potential as a promising species for enhancing photosynthetic carbon uptake on green roofs in southeastern coastal cities.