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Tra c congestion is one of serious problems in cities; rainfalls would exacerbate tra c congestion, and thus result in huge economic losses. However, limited studies focused on how rainfalls in uenced tra c congestion and its associated economic losses. Based on detailed hourly data, we estimated how tra c congestion index (TCI) changed with different rainfall intensities in the Beijing-Tianjin-Hebei (BTH) region, China, and we also explored their economic losses. The results illustrated that all cities presented the similar trend of daily tra c congestion, and morning peak occurred 2 hours later on holidays than workdays. Rainfall had signi cant impacts on tra c congestion for most time windows, except midnight. Tra c congestion increased with rainfall intensities, but smaller cities were more vulnerable to rainfall intensity than megacities. Rainfalls led to 0.98 billion yuan of extra economic losses in 2019, 38% of which occurred under heavy rainfalls. Tra c congestion in 2019 caused a total economic cost of 31.5 billion yuan in the BTH region (0.4% of its GDP), including the recurrent cost and economic losses due to rainfalls; besides, the social cost and direct cost contributed the same share of 49.4%, with 1.2% from the environmental costs. Considering future urban development and climate change, it is bene cial to establish the climate-resilient transportation system for avoiding future serious tra c congestion as well as huge economic losses in future.

Most cities in China, especially industrial cities, are facing severe air pollution, which affects the health of the residents and the development of cities. One of the most effective ways to alleviate air pollution is to improve the urban ventilation environment; however, few studies have focused on the relationship between them. The Frontal Area Index (FAI) can reflect the obstructive effect of buildings on wind. It is influenced by urban architectural form and is an attribute of the city itself that can be used to accurately measure the ventilation capacity or ventilation potential of the city. Here, the FAIs of 45 industrial cities of different sizes in different climatic zones in China were computed, and the relationship between the FAI and the concentration of typical pollutants, i.e., NO2, were analyzed. It was found that (1) the FAIs of most of the industrial cities in China were less than 0.45, indicating that most of the industrial cities in China have excellent and good ventilation capacities; (2) there were significant differences in the ventilation capacities of different cities, and the ventilation capacity decreased from the temperate to the tropical climate zone and increased from large to small cities; (3) there was a significant difference in the ventilation capacity in winter and summer, indicating that that with the exception of building height and building density, wind direction was also the main influencing factor of FAI; (4) the concentration of NO2 was significantly correlated with the FAI, and the relative contribution of the FAI to the NO2 concentration was stable at approximately 9% and was generally higher than other socioeconomic factors. There was a turning point in the influence of the FAI on the NO2 concentration (0.18 < FAI < 0.49), below which the FAI had a strong influence on the NO2 concentration, and above which the influence of the FAI became weaker. The results of this study can provide guidance for suppressing urban air pollution through urban planning.

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