Spatiotemporal variations of cold waves and regional extreme low temperature along the Middle Route of South-to-North Water Transfers Project
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Abstract:
In cold regions, such as high latitudes during winter, rivers and water conveyance channels often experience the phenomenon of freezing under low temperature conditions. During the initial stage of freezing and the subsequent melting stage, ice floes are prone to get stuck in the channels, forming ice jams and dams, which obstruct the flow of water and raise the water level in the channels, thus adversely affecting winter water transfer. Cold waves and extreme low temperatures in the region often cause significant temperature fluctuations, which are the main factors influencing changes in the ice conditions of rivers and channels. The Middle Route of South-to-North Water Transfers Project (MRSWTP) spans multiple latitudes, and the areas north of the Yellow River are affected by ice conditions to varying degrees every year during winter operations. Therefore, analyzing the spatiotemporal variations of cold waves and regional extreme low temperatures along the MRSWTP is of great significance for ice disaster prevention, winter water transportation scheduling, and other related issues.Based on the daily minimum and maximum air temperature data of meteorological stations within a width of 40 km along the route from the head of Taocha Drainage Canal to the Beijuma Culvert of the MRSWTP from 1960 to 2020, the occurrences of cold waves and five extreme cold climate indices were calculated. The Sen’s slope estimator method was employed to analyze their trends. Additionally, the spatial variations of the five extreme climate indices were analyzed using the inverse distance weighting spatial interpolation method based on temperature data from 56 meteorological stations.The results show that among the nine typical weather stations selected, the frequency of cold waves in seven weather stations decreased from 1960 to 2020. The frequency of cold waves in Anyang and Baoding stations showed a downward trend, but since 2000, the number of cold waves has increased significantly. January has the highest frequency of cold waves occurrences, followed by December, February, and November. The regions north of Xingtai show an increasing trend in cold waves occurrence with rising latitudes. As for the extreme climate indices, the minimum value of the annual minimum temperature at the nine meteorological stations generally exhibits an increasing trend from 1960 to 2020. However, since 1990, Baoding station has shown an abnormal trend of not increasing but rather decreasing, while Xingtai and Shijiazhuang stations have remained in a state of stagnation without further increase. The other four extreme climate indices, including frost days (the number of days with a daily minimum temperature below 0 ℃) and freeze days (the number of days with a daily maximum temperature below 0 ℃), generally exhibit different decreasing trends, but some stations show abnormal trends of not decreasing but instead increasing or stagnating. Moreover, it is found that the decline rate of the number of days with a daily minimum temperature below 0 ℃ is faster compared to the decline rate of the number of days with a daily maximum temperature below 0 ℃, indicating a more significant impact of climate change. There is no consistent trend detected among the various climate indices in terms of spatial changes. For freeze days, the decline rate along the MRSWTP from south to north shows an accelerating trend.Under the overall trend of global climate warming, the frequencies of cold waves and extreme low-temperature weather along most regions of the MRSWTP have been slowing down, but there have been obvious intensifications observed in some regions since the 21st century. The winter water conveyance flow rate of the project will be further increased to meet the water demands for production, living, and ecology in northern cities. In future winter high-flow water conveyance plans, the impacts of severe cold waves and extreme low temperatures on winter water conveyance should be considered to reduce the risk of ice disasters.
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