Carbon emission reduction from the cooling effect of urban greenspace in the three urban agglomerations in China

Urban greenspace has the ability to cool the surrounding environment, thereby reducing energy consumption caused by the urban heat island effect and increasing the carbon savings. However, the underlying influential factors associated with these carbon savings have not been fully explored. This study estimated the amount of carbon saving by the urban greenspace patches through the local cooling effect in 48 cities in the Yangtze-River-Delta agglomeration (YRD), Jing-Jin-Ji agglomerations (JJJ), and the Great Bay Area (GBA) and explored the factors with carbon saving across these cities. Results showed that a total amount of 353 × 103 t of carbon was saved by the urban greenspace in these 48 cities, with an average of 7345 t of carbon saving per city. Carbon saved by the surrounding cooled areas (4542t, 3253 t, and 204 t of carbon saving by the surrounding cooled area for YTZ, JJJ, and GBA, respectively) was nearly similar to that by the urban greenspace patches themselves (5371 t, 3550 t, and 160 t of carbon saving by the urban greenspace patches themselves for YTZ, JJJ, and GBA, respectively). Differences were found in the carbon saving among the three urban agglomerations (P < 0.01), with the largest amount of carbon saving in YRD (9913 t per city) and then followed by JJJ (6803 t per city) and GBA (364 t per city). Principal component analysis and regression analysis showed that the amount of carbon saving by urban greenspace across cities was significantly related to the geometric characteristics of urban greenspace and the level of urban socio-economic development, while the correlation with urban greenspace pattern was relatively weak. It is indicated that the urban greenspaces should be protected, especially in those cities with high levels of socio-economic development. These results also demonstrate the carbon saving by urban greenspace through its local cooling effect should not be neglected.