Spatial and temporal distribution characteristics of late spring coldness and its meteorological indexes in Hebei province during 1991-2020

Using the observational data of daily temperature from 76 national meteorological stations in Hebei province from March to May during 1991-2020, the spatial and temporal characteristics of late spring coldness were analyzed using the methods of Mann-Kendall test, GIS spatial interpolation and linear regression.The results showed that the accuracy of "Meteorological index of late spring coldness" in screening the process of late spring coldness was 63.6%, with satisfied applicability.The number of late spring coldness occurrence was 2094 from 1991 to 2020 in Hebei province, with the mild occurring the most, followed by moderate, and the severe occurring the least.In terms of the spatial distribution, the number of the mild late spring coldness increased from south to north, the moderate-severe increased from the middle to the north and the south, with the most distributed in the northern plateaus and mountains.The inter-annual variation of late spring coldness showed a downward trend, with the most obvious decline happening in central Hebei province.In terms of total duration days, the mild decreased from northeast to southwest, and moderate-severe decreased from the northern plateau, Yanshan mountain area, Taihang mountains to the plains.The inter-annual variation of total duration days of late spring coldness in southern and central Hebei province showed a downward trend.The daily minimum temperature decreased in a stepwise manner from south to north, with minimum temperature in the north of Hebei province far below the south and central of Hebei province.The degree of daily temperature reduction decreased in a stepwise manner from south to north in March and May.In central Hebei province, the number of moderate-severe late spring coldness was large from April 9 to 12, while in the north of Hebei province, the total number of late spring coldness and the number of moderate-severe in early May were relatively high.