Carbon mitigation potential afforded by rooftop photovoltaic in China.

Rooftop photovoltaics (RPVs) are crucial in achieving energy transition and climate goals, especially in cities with high building density and substantial energy consumption. Estimating RPV carbon mitigation potential at the city level of an entire large country is challenging given difficulties in assessing rooftop area. Here, using multi-source heterogeneous geospatial data and machine learning regression, we identify a total of 65,962 km2 rooftop area in 2020 for 354 Chinese cities, which represents 4 billion tons of carbon mitigation under ideal assumptions. Considering urban land expansion and power mix transformation, the potential remains at 3-4 billion tons in 2030, when China plans to reach its carbon peak. However, most cities have exploited less than 1% of their potential. We provide analysis of geographical endowment to better support future practice. Our study provides critical insights for targeted RPV development in China and can serve as a foundation for similar work in other countries.

Coupling urban 3-D information and circuit theory to advance the development of urban ecological networks.

Ongoing, rapid urban growth accompanied by habitat fragmentation and loss challenges biodiversity conservation and leads to decreases in ecosystem services. Application of the concept of ecological networks in the preservation and restoration of connections among isolated patches of natural areas is a powerful conservation strategy. However, previous approaches often failed to objectively consider the impacts of complex 3-D city environments on ecological niches. We used airborne lidar-derived information on the 3-D structure of the built environment and vegetation and detailed land use and cover data to characterize habitat quality, niche diversity, and human disturbance and to predict habitat connectivity among 38 identified habitat core areas (HCAs) in Nanjing, China. We used circuit theory and Linkage Mapper to create a landscape resistance layer, simulate habitat connectivity, and identify and prioritize important corridors. We mapped 64 links by using current flow centrality to evaluate each HCA's contribution and the links that facilitate intact connectivity. Values were highest for HCA links located in the west, south, and northeast of the study area, where natural forests with complex 3-D structures predominate. Two smaller HCA areas had high centrality scores relative to their extents, which means they could act as important stepping stones in connectivity planning. The mapped pinch-point regions had narrow and fragile links among the HCAs, suggesting they require special protection. The barriers with the highest impact scores were mainly located at the HCA connections to Purple Mountain and, based on these high scores, are more likely to indicate important locations that can be restored to improve potential connections. Our novel framework allowed us to sufficiently convey spatially explicit information to identify targets for habitat restoration and potential pathways for species movement and dispersal. Such information is critical for assessing existing or potential habitats and corridors and developing strategic plans to balance habitat conservation and other land uses based on scientifically informed connectivity planning and implementation.

Acoplamiento de la Información Urbana en 3-D y la Teoría de Circuitos para Avanzar el Desarrollo de las Redes Ecológicas Urbanas Resumen El rápido crecimiento urbano en curso acompañado por la fragmentación y pérdida de hábitats obstaculizan la conservación de la biodiversidad y llevan a una disminución de los servicios ambientales. La aplicación del concepto de redes ecológicas en la preservación y restauración de las conexiones entre los fragmentos aislados de áreas naturales es una estrategia poderosa para la conservación. Sin embargo, las estrategias previas con frecuencia han fallado al no considerar de manera objetiva los impactos del ambiente complejo y tridimensional que tienen las ciudades sobre los nichos ecológicos. Usamos información derivada de lidar aéreos sobre la estructura tridimensional del ambiente construido y de la vegetación y detallamos la información sobre el uso y la cobertura del suelo para caracterizar la calidad del hábitat, la diversidad de nichos y la perturbación humana y así predecir la conectividad de hábitat entre 38 áreas nucleares de hábitat (ANHs) en Nanjing, China. Usamos la teoría de circuitos y el programa Linkage Mapper para crear una capa de resistencia de paisaje, simular la conectividad de hábitat e identificar y priorizar los corredores importantes. Mapeamos 64 conexiones mediante la centralidad del flujo de corriente para evaluar la contribución de cada ANH y las conexiones que facilitan la conectividad intacta. Los valores más altos fueron para las conexiones de ANH ubicadas en el oeste, sur y norte del área de estudio, en donde predominan los bosques naturales con estructuras tridimensionales complejas. Dos áreas más pequeñas de ANH tuvieron puntajes altos de centralidad en relación con sus extensiones, lo que significa que podrían fungir como pasos intermedios importantes en la planeación de la conectividad. Las regiones mapeadas de los puntos de fijación tuvieron conexiones estrechas y frágiles entre las ANHs, lo que sugiere que requieren de protección especial. Las barreras con los puntajes más elevados de impacto estuvieron localizadas principalmente en las conexiones entre las ANH y la Tierra de las Montañas Púrpuras. Con base en estos puntajes elevados hay mayor probabilidad de que indiquen localidades importantes que pueden ser restauradas para mejorar el potencial de las conexiones. Nuestro novedoso marco de trabajo nos permitió transmitir adecuadamente la información espacialmente explícita para identificar los objetivos de la restauración de hábitat y los caminos potenciales para el movimiento y la dispersión de las especies. Tal información es crítica para el análisis de los hábitats y corredores existentes o potenciales y para el desarrollo de planes estratégicos para equilibrar la conservación del hábitat y otros usos de suelo con base en la planeación e implementación de la conectividad científicamente informada.

Determination of runoff response to variation in overland flow area by flow routes using UAV imagery.

Surface runoff can be routed to both pervious areas (PAs) and drainage systems during an overland flow. Excessive runoff from an impervious area (IA) flowing into a drainage system causes an overload, which can be relieved by diverting runoff to PAs. However, the hydrological link between IAs and PAs, especially the runoff response to variation in overland flow areas (OFAs), has not well been considered in runoff simulations due to the complexity of routing. To understand how the OFA within an IA contributes to runoff generation, a novel classification approach was applied to categorize the IA in a study area in Nanjing University, Xianlin campus, China into directly connected impervious area (DCIA) and indirectly connected impervious area (ICIA) by flow routes using high-resolution ground-based images (0.5 m) from an unmanned aerial vehicle. The OFAs then include DCIA and the total impervious area (TIA), which is the sum of DCIA and ICIA. The runoff simulations were supported by Storm Water Management Model (SWMM) calibrated with observed rainfall and runoff data. The resulting proportions of DCIA and ICIA of the study area were 34.13% and 10.99%, respectively. The spatial distributions of DCIA and ICIA are characterized by the subcatchment landscape heterogeneity resulting from vegetation, imperviousness, and slope. The observed runoff coefficients and peak flows were positively correlated with the percentages of DCIA and TIA. The runoff coefficient was significantly correlated with the DCIA in a light rainfall event of 18.4 mm (R2 =0.82) and with the TIA in a heavy rainfall event of 119 mm (R2 =0.92). Runoff generation is affected by both the characteristics of the rainfall event and the accompaning variations in OFAs. Results indicate that increasing of the flow connectivity from IAs to PAs and increasing the water retention capacity of PAs may be effective strategies for optimizing landscape patterns for stormwater management.

Mining the Urban Sprawl Pattern: A Case Study on Sunan, China.

China's urbanization is going into a fast development stage. This paper focuses on the recent evolution of an urbanized area - Sunan, the southern part of Jiangsu province in the Yangtze River Delta in China - by means of complementary approaches, especially different fractal and autocorrelation measures. The research shows that Sunan's urban clusters are becoming more and more homogenous and compact and are growing up along the important transportation axes. The enriching discussion of the findings establishes the links between the morphology of urban sprawl and recent socio-economic changes in China.