Urban metabolism and emergy of China's cities

The unprecedented pace of urbanization and industrialization caused a massive increase in China's urban metabolic pressure. The trend presents an urgent need for detailing the long-term changes and disparities in urban metabolic performances in a wide range of cities. However, existing studies rarely evaluate cities of large spatial ranges for long time periods. Here, we present empirical evidence of 281 China's cities from 2000 to 2020 based on emergy analysis. We categorized the 281 cities in six types, namely agricultural cities, light manufacturing cities, energy production cities, heavy manufacturing cities, service-based cities, and high-tech cities. We found that China's urban metabolic performance gradually became worse. At national level, total emergy use increased more than six times, but the annual growth rate slowed down between 2000 and 2020. The environmental sustainability index of China's cities in total decreased by 83.61 %. At city level, emergy-based performances among the six types of cities showed considerable differences. Agricultural cities and light manufacturing cities had better sustainability; service-based cities faced high environmental pressure. In addition, we investigated future urban metabolic performance and potential improvements based on the five-year development policy. Scenarios based on existing policies showed that total emergy use would experience slower growth, and most cities continue their decline in emergy metabolism performances in 2025. We provided city-specific policy recommendations to typical cities in six city types. Our data and results gave a holistic view of China's city-level metabolic performances at national scale with a broad spatial coverage and for a long period of time.