Study on characteristics and forecasting methods of road icing in Xizang

Using hourly observation data from traffic meteorological stations in Xizang from 2018 to 2021,this study analyzed the characteristics of road icing and meteorological factors in Xizang.A road icing forecasting model was constructed and its accuracy was verified.The results showed that the number of road icing days in Xizang decreased from the northwest to the southeast and was positively correlated with altitude.Road icing was caused by snowfall (sleet or snow) and road snow cover,with snowfall icing accounting for 58% of the total road icing days in Xizang,and snow cover icing accounting for 42%.Specifically,the northwestern part of Xizang was dominated by snow cover icing,while the central and southeastern parts were dominated by snowfall icing.Road icing occurred from September to June of the following year,with the highest number of icing days in January and February,and the icing period was mainly concentrated from 02:00 to 11:00.During road icing events,the 0%-75% quantile ranges of ground temperature,air temperature,and wind speed were below -2 ℃,1 ℃,and 8 m·s^-1,respectively; while the 25%-100% quantile ranges of relative humidity,24h accumulated snowfall and snow depth were above 50%,0.1 mm,and 0 cm,respectively.This indicated that meteorological conditions with low ground and air temperatures,low wind speed,high relative humidity,and snowfall or snow cover were favorable for road icing.Based on the above characteristics,the Xizang road icing forecasting model was constructed and divided into 4 index levels.After verifying the graded forecast of road icing at single stations in the past 2 years,the average forecast accuracy of each level reached 77%.