Evaluation of comprehensive cold intensity in winter at Zhuozhou Station of South-to-North Water Diversion Middle Route Project

To enhance understanding of extreme winter meteorological conditions, particularly comprehensive cold intensity along the South-to-North Water Diversion Middle Route Project, based on the daily average temperature data in winter from 1981 to 2021 at Zhuozhou Meteorological Station, which is located at the northern end of the open channel section of Middle Route main canal, three key factors, namely days with sub-zero temperatures, minimum daily extreme temperature and cumulative negative accumulated temperature, were selected to construct the Winter Composite Cold Index (WCCI).A quantitative analysis of the comprehensive cold degree in winter at Zhuozhou Station over the past 41 years was carried out.The research results showed that: In early December, the daily average temperature approached 0 ℃, gradually declining to an annual minimum of approximately -4 ℃ between late December and mid-January, followed by recovery to above 0 ℃ by mid-February, with January being the coldest month.The winter cold intensity was relatively high from 1981 to 1987 and from 2000 to 2021, peaking in 2013, while it was lower from 1988 to 1999.For January, the coldest year was 2000, followed by 2001 and 2013.From 2014 to 2021, when the middle route of the South-to-North Water Diversion Project was officially put into operation, the winter of 2021 at Zhuozhou Station had the highest overall coldness level, with the WCCI reaching -1.82, and January 2016 showed the coldest monthly value (WCCI=-2.92).These two values were significantly higher than historical extremes (-5.08 and -4.93) by 64.17% and 40.77%, respectively, indicating that the project has not yet faced extreme winter conditions during the eight years of the project operation.This research provides a scientific basis for comprehensive assessment of the cold intensity in winter along the Middle Route Project, such as the quantitative identification of extremely cold years, the dynamic scheduling of water diversion during the ice period, and the prevention of ice-related disasters and emergency response.