北回归线纵向岭谷区干湿日时空变化特征

Spatiotemporal Variation Characteristics of Dry/Wet Spells in Longitudinal Range-Gorge Region of the Tropic of Cancer

在全球变暖背景下,极端气候事件频发,从多角度了解降水量的变化对水资源的利用具有重要意义。利用纵向岭谷区北回归线沿线1961—2019年24个站日降水量计算14个干湿日指数,基于修订的Mann-Kendall检验、Pettitt、小波相干等方法揭示了干湿日指数时空变化特征及与大尺度环流指数相关性。结果表明:①北回归线纵向岭谷区湿日事件呈显著减少趋势,干日事件呈增多趋势,尤其是北回归线以南元江以西,大多数站点干湿日指数突变年主要集中在2002年;②短历时湿日事件发生频率及对年降水量贡献率呈现上升趋势,中长历时湿日事件呈现减少趋势;短历时干日事件呈现减少趋势,中长历时干日事件呈增多趋势,整个地区呈现干旱化;③极端干日指数与ENSO密切相关,其存在约6年负相关共现周期;极端湿日指数与南海夏季风密切相关,其存在约8年正相关共现周期。通过以上分析表明北回归线纵向岭谷区干湿日指数整体上表现为干旱化趋势,这意味着干旱风险呈增加趋势,其时空变化特征及局部差异可能与大尺度环流指数、季风和岭谷区“通道-阻隔”作用共同影响密切相关。

Under the background of global warming,extreme climate events occur frequently.Understanding the change in precipitation from multiple perspectives is of great significance to the utilization of water resources.Specifically,the daily precipitation data at 24 stations along the Tropic of Cancer in the Longitudinal Range-Gorge Region(LRGR)from 1961 to 2019 are used to calculate 14 wet/dry spell indices.Methods including the revised Mann-Kendall test,Pettitt,and wavelet coherence are adopted to reveal the spatiotemporal variation characteristics of the dry/wet spell indices and their correlation with the large-scale circulation index.The results indicate that:①the wet and dry spells in LRGR of the Tropic of Cancer show a significant decreasing and increasing trend,respectively,especially in the area west of Yuanjiang River and south of the Tropic of Cancer.The change in the wet and dry spell indices of most stations is mainly concentrated in 2002.②The frequency of short-duration wet spells and the contribution rate to annual precipitation demonstrate an increasing trend,and those of the medium-long-duration wet spells demonstrate a decreasing trend;the short-duration dry spells are in decline while medium-long-duration dry spells are rising,and the entire region tends to aridification.③The extreme dry spell index is closely related to ENSO,and it has a negatively correlated co-occurrence cycle of about six years;the extreme wet spell index is closely related to the summer monsoon of the South China Sea,and it has a positively correlated co-occurrence cycle of about eight years.To sum up,the above analysis shows that dry and wet spell indices in LRGR of the Tropic of Cancer demonstrate an overall trend of aridification,which means that the drought risks are increasing.Their spatiotemporal variation characteristics and local differences may be closely related to the joint influence of the large-scale circulation index,monsoon,and channel-blocking in LRGR.