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Rapid global urbanization and its progress have profoundly affected urban vegetation. The ecological quality of urban vegetation is a vital indicator of regional ecological stability and health. A comprehensive assessment of the coupling coordination and coercive relationship between urbanization and the vegetation ecological quality is essential for promoting sustainable regional green development. Using the rapidly urbanizing Guangdong–Hong Kong–Macao Greater Bay Area (GBA) urban agglomeration in China as an example, this study evaluates the vegetation quality condition and the level of urbanization and explores the dynamic relationship between vegetation ecological quality and urbanization processes. This study introduces the vegetation ecological quality index (VEQI) based on net primary productivity (NPP) and fractional vegetation cover (FVC), as well as the comprehensive urbanization index (CUI) derived from gross domestic production (GDP), population density, and nighttime lighting data. The coupling coordination and Tapio decoupling models are employed to assess the degree of coupling coordination and the decoupling relationship between the VEQI and CUI across different periods. The results showed that (1) from 2000 to 2020, the VEQI in the GBA showed a significant increase, accompanied by continuous urbanization, particularly evident with the high CUI values in central areas; (2) the coupling coordination degree (CCD) exhibits high values and significant change slopes in the central GBA, indicating dynamic interactions between urbanization and vegetation ecological quality; (3) the decoupling states between the VEQI and CUI are dominated by weak decoupling (WD), strong decoupling (SD), expansive negative decoupling (END), and expansive coupling (EC), suggesting improvements in the relationship between urbanization and vegetation ecological quality; (4) the coordinated development level of the VEQI and CUI in the study area shows improvement, and their decoupling relationship displays a positive trend. Nevertheless, it remains crucial to address the impact of urbanization pressure on vegetation ecological quality and to implement proactive measures in response. The results of this study provide theoretical support for mesoscale development planning, monitoring vegetation ecological conditions, and formulating environmental policies. [ABSTRACT FROM AUTHOR]

As two main drivers of vegetation dynamics, climate variability and human activities greatly influence net primary productivity (NPP) variability by altering the hydrothermal conditions and biogeochemical cycles. Therefore, studying NPP variability and its drivers is crucial to understanding the patterns and mechanisms that sustain regional ecosystem structures and functions under ongoing climate variability and human activities. In this study, three indexes, namely the potential NPP (NPPp), actual NPP (NPPa), and human-induced NPP (NPPh), and their variability from 2000 to 2020 in the Guangdong–Hong Kong–Macao Greater Bay Area (GBA) were estimated and analyzed. Six main scenarios were generated based on change trends in the three indexes over the past 21 years, and the different relative impacts of climate variability and human activities on NPPa variability were quantitatively analyzed and identified. The results showed that the NPPp, NPPa, and NPPh had heterogeneous spatial distributions, and the average NPPp and NPPa values over the whole study area increased at rates of 3.63 and 6.94 gC·m−2·yr−1 from 2000 to 2020, respectively, while the NPPh decreased at a rate of −4.43 gC·m−2·yr−1. Climate variability and the combined effects of climate variability and human activities were the major driving factors of the NPPa increases, accounting for more than 72% of the total pixels, while the combined effects of the two factors caused the NPPa values to increase by 32–54% of the area in all cities expect Macao and across all vegetation ecosystems. Human activities often led to decreases in NPPa over more than 16% of the total pixels, and were mainly concentrated in the central cities of the GBA. The results can provide a reference for understanding NPP changes and can offer a theoretical basis for implementing ecosystem restoration, ecological construction, and conservation practices in the GBA. [ABSTRACT FROM AUTHOR]

• Inter-calibration between DMSP-OLS and NPP-VIIRS were conducted at the pixel scale. • CO 2 emissions in both lit area and unlit area were estimated. • Tradeoff between vegetation CO 2 sequestration and fossil CO 2 emission was evaluated. • Policy implications for CO 2 emissions reduction were suggested. Carbon neutrality has attracted tremendous attention. Cities contribute the most to CO 2 emissions. However, the contribution of vegetation to fossil-fuel-related CO 2 emissions in urban agglomeration is unclear. Clarifying the trade-off role of vegetation can disaggregate carbon reduction targets down to sub-units to adapt to and even mitigate global warming. In this study, the Guangdong–Hong Kong–Macao Greater Bay Area (GBA), one of the world's largest metropolitan areas, was studied using our proposed inter-calibration method. The results showed that the inter-calibration method is satisfactory and that the EANTLI model effectively decreases the blooming and saturation effects of nighttime light. In addition, fossil-fuel-related CO 2 emissions increased significantly (P < 0.0001) in the GBA during 2000–2018, while the variation in CO 2 sequestrations was far lower than that in the increase in emissions. CO 2 sequestrations by vegetation fully offset fossil-fuel-related CO 2 emissions in 2000, while the status reversed after 2001. Our findings illustrate the role of vegetation carbon sequestration in offsetting fossil-fuel-related CO 2 emissions and emphasize the importance of a CO 2 budget. Additionally, the one city, one policy strategy is a good choice for further adapting to and mitigating global warming. [ABSTRACT FROM AUTHOR]