京津冀地区倒春寒时空特征及风险概率统计分析

Statistical Analysis of Spatial and Temporal Characteristics and Risk Probability of Late Spring Coldness in Beijing-Tianjin-Hebei Region

利用京津冀99个国家气象站1961-2020年3-5月日气温数据,应用MK趋势检验等方法,分析倒春寒发生频次、持续天数和站次比时空分布规律,基于信息扩散理论评估不同等级倒春寒风险概率。结果表明:近30年99个国家气象站共发生2570次倒春寒,轻度最多,重度最少。发生频次上,轻度和中度由北向南递减,重度自东北向西南递减,4月轻度、中-重度和发生总次数均最多,年际变化呈下降趋势,其中3-5月和5月显著下降。总持续天数上,轻度和重度由东北向西南递减,中度呈南北高、中间低的格局。各站轻度平均持续天数相差不大,中度和重度则差异明显,平均持续天数随着等级的增大而跃增。年均倒春寒持续天数为6.9 d·a^(-1),呈下降趋势,降幅为1.5 d·(10a)^(-1)。88.9%的站点持续天数呈年际下降趋势,35个站显著下降,南部比北部降幅更大。3-5月和5月站次比年际下降趋势显著,4月轻度和中-重度站次比均最高,各月轻度站次比均远高于中-重度。倒春寒风险随着等级升高呈阶梯式降低,轻度2年一遇以下约占34.3%的站点,主要在北京、石家庄、邢台和邯郸等地;中度5~10年一遇和10年一遇以下的站点约占90%,前者集中在京津冀南北两端,后者大多位于京津冀中部。研究区重度倒春寒风险均较低,高达97.0%的站点为25年一遇以下。

Based on the daily temperature data of 99 national meteorological stations in Beijing-Tianjin-Hebei region from March to May 1961 to 2020,the statistical methods such as Mann-Kendall trend test were used to analyze spatial and temporal distribution characteristics of late spring coldness from frequency,duration days and ratio of occurring stations to all stations,and the risk probability of different levels of late spring coldness was evaluated based on the information diffusion theory.The results indicated that:In the past 30 years,2570 cases of late spring coldness occurred at 99 national meteorological stations,with the mildest and the least severe.In terms of frequency,the mild and moderate late spring coldness decreased from north to south,while severe late spring coldness decreased from northeast to southwest,the mild,moderate-severe and the total late spring coldness were most in April,the inter-annual occurrence frequency showed a downward trend,with a significant decrease from March to May and May.In terms of total duration days,mild and severe late spring coldness decreased from northeast to southwest,with moderate late spring coldness showing a pattern of high in north and south and low in middle.The average duration days of mild late spring coldness at each station was not significantly different,while the difference was significant in moderate and severe late spring coldness,the average duration days increased sharply with the increase of level.The annual mean duration days of late spring coldness was 6.9 d·a^(-1),showing a downward trend,with a decrease rate of 1.5 d·(10a)^(-1).The ratio of the stations showed an inter-annual downward trend in duration days was 88.9%,with 35 stations showing a significant decrease and the southern region experiencing a greater decrease than the northern region.The inter-annual downward trend in ratio of late spring coldness stations in March to May and May was significant,with the highest ratios of mild and moderate-severe late spring coldness in April,and the ratio of mild late spring coldness was much higher than that of moderate-severe late spring coldness in each month.The risk of late spring coldness decreased in a stepwise manner as the level increased,The stations with risk was mild and a return period of about 2 years or less was about 34.3%of all stations,mainly in Beijing,Shijiazhuang,Xingtai and Handan;The stations with risk was moderate and a return period of 5~10 years and 10 years or less was about 90%of all stations,and the former was concentrated at the north and south ends of Beijing-Tianjin-Hebei region,while the latter was mostly located in the central part of Beijing-Tianjin-Hebei region.The risk of severe late spring coldness in the research area was relatively low,with up to 97%of severe stations with a return period of about 25 years or less.