The Pace of Urbanization Regulates Global Urban Gross Primary Productivity Trends
Han Chen, Bo Liu, Yaping Deng, Siyi Wang, Tiejun WangAbstract
Urban expansion replaces vegetated land with impervious surfaces, significantly reducing urban Gross Primary Productivity (GPP u ). Conversely, rising CO 2 levels and warming associated with climate change can enhance GPP u . The interplay between these opposing effects on GPP u remains poorly understood, resulting in considerable uncertainties for estimating the long‐term dynamics of urban carbon storage. Using an improved Carnegie‐Ames‐Stanford approach (CASA) model that accounts for urban CO 2 , we evaluated the long‐term trends and driving factors of GPP u in 2126 cities worldwide, spanning both historical and future periods. The study revealed that the average urban expansion rate (UER) of global cities from 1982 to 2024 was 21.3 km 2 /year. Rapid urban expansion was predominantly observed in cities in China and North America; whereas, cities in Europe exhibited relatively slower expansion rates. The response of GPP u to urban expansion was found to be dependent on the UER. In cities with faster UERs than 5.83 km 2 /year, the negative impact of urban expansion surpassed the positive effects of climate change on long‐term GPP u , resulting in a downward trend in GPP u (−2.48 g C/m 2 /year). Conversely, in cities with slower UERs (commonly observed in Europe), an opposite pattern was observed, leading to an upward trend in GPP u (1.21 g C/m 2 /year). The projected future response and driving factors of GPP u to urbanization were expected to resemble those observed in the historical period. These findings highlight that the pace of urbanization acts as a fundamental regulator of GPP u , underscoring the need for growth‐rate‐specific strategies to sustain regional carbon sequestration.