Rainfall can bring uncertainties to the traffic flow and influence the normal function of urban transportation systems.The impact of pre-cipitation on the urban traffic flow,especially the different impacts among cities and areas within a city,is worth investigating.Here,we analysed the impact of precipitation on the traffic flow in the urban areas of the Beijing-Tianjin-Hebei region by comparing the traffic flow in non-precipitation and rainy weather with different hourly precipitation intensities in 2021.The increase in the travel time index(TTI)is chosen to represent the influence of precipitation on the transportation system.The results show that the maximum of the average TTI increases on the city scale under various rainfall intensities by 3.3％,6.6％and 10.8％in Beijing,Tianjin and Shijiazhuang,respectively.In general,the increase in the TTI contributed by precipitation is the greatest at morning and afternoon peak hours,and the traffic congestion degree increases with the rainfall intensity.However,in the morning peak,afternoon peak and midday hours in Beijing and Tianjin,the influences of the weak rainfall intensity on the traffic flow are generally great,whereas the traffic congestion degree caused by heavy precipitation is relatively low.Particularly,in morning peak hours,the congestion reduction reaches approximately 2％,which may be related to the spatial difference in the impacts of precipitation on the traffic flow and the changes in people's travel intention under different rainfall intensities.The findings can help better understand the relationship between rainfall and urban traffic flow characteristics and also potentially contribute to the development of impact-oriented climate predictions.

Tianjin Climate Center,Tianjin Meteorological Service,Tianjin 300074,China;National Climate Center China Meteorological Administration,Beijing 100081,China;Tianjin Meteorological Observatory,Tianjin Meteorological Service,Tianjin 300074,China

[1]Ming-Ming XIONG;Zhen-Yu HAN;Bo LU;Jun GUO;Shu XU;Yan-Juan YANG;He HUANG-.Effects of rainfall on the weekday traffic flow in major cities of the Beijing-Tianjin-Hebei region,China,in 2021)[J].气候变化研究进展（英文版）,2022(06):858-867

weekday

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