西藏地区一种新的四季划分方法

A new method of four seasons division in Tibet

利用西藏地区38个气象站点1981—2022年逐日气温资料,分析常用气候季节划分方法在西藏地区的适用性,指出各种季节划分方法的不足和局限,基于西藏物候和主要农作物生育期提出的季节划分气温阈值等指标,筛选出适于西藏地区的季节划分方法及气温阈值,分析了西藏地区的四季开始日和长短的变化特征。结果表明:(1)常用气候季节划分方法在西藏地区应用有一定的局限性,而西藏物候季节划分方法和生育期季节划分方法适用于西藏高原地区的农事活动。(2)基于阈值“6℃、15℃”“5℃、16℃”“6℃、16℃”和“6℃、17℃”分析典型气象站四季时间长度变化特征发现,改则冬季时间长度长于其他季节、察隅夏季时间长度长于其他季节,且拉萨、昌都、改则、察隅四季长度均呈现夏季上升和秋冬季下降的趋势。(3)拉萨和昌都的夏季平均气温进行突变检验发现两站分别于2011年和2017年出现突变,佐证了夏季阈值取17℃的合理性。(4)西藏新四季划分法指标为“6℃、17℃”,该指标划分西藏四季发现,夏季站点主要分布在雅鲁藏布江一线的较低海拔地区;春、秋季持续时间整体呈现西北部和南部偏短、中东部偏长的特征,夏季呈现中部偏长、四周偏短的特点,冬季与春秋季则相反;四季时空特征符合西藏地区实际情况。春、夏、秋、冬季平均开始日分别为3月21日、6月16日、7月25日、11月3日。

This study evaluates the applicability of common climatic seasonal division methods in Tibet of China,utilizing daily temperature data from 38 meteorological stations spanning from 1981 to 2022.The analysis highlights the limitations of various seasonal division approaches and emphasizes the suitability of Tibetan phenological and growing season division methods for agricultural activities in Plateau region of Tibet.Temperature thresholds for seasonal division were determined based on Tibetan phenology and the main crops’growing periods.The research reveals that:(1)While general methods for climatic season division exhibit certain limitations in Tibet,the Tibetan phenological and growing season division methods align well with agricultural requirements.(2)Employing temperature thresholds of“6℃,15℃”,“5℃,16℃”,“6℃,16℃”,and“6℃,17℃”,the study analyzes the variation in the lengths of the four seasons at typical weather stations.Gerze experiences a longer winter,while Zayu has a prolonged summer.In Lhasa,Qamdo,Gerze,and Zayu stations,summer durations have extended,whereas autumn and winter have contracted.(3)Mutation tests indicate that the average summer temperatures at Lhasa and Qamdo stations underwent significant changes in 2011 and 2017,respectively,supporting the use of 17℃as the summer threshold.(4)The newly proposed four-season division method for Tibet,characterized by the“6℃,17℃”index,demonstrates a distribution pattern of weather stations mainly along the lower elevation areas of the Yarlung Tsangpo River Line during summer.Spring and autumn durations are shorter in the northwest and south,and longer in the central and eastern regions.Conversely,summer is extended in the central areas and reduced in the peripheral regions,with the opposite pattern observed for winter,spring,and autumn.This spatiotemporal distribution aligns with Tibet’s climatic reality.The average onset dates for spring,summer,autumn,and winter are March 21,June 16,July 25,and November 3,respectively.