重庆市伏秋旱时空演变特征及其影响因素分析

Spatial-temporal Variation and Impact Factors of the Mid Summer and Autumn Drought Events in Chongqing,China

伏秋旱是指发生在夏季或秋季的干旱现象,在重庆市较为多发且造成的灾害损失较大。基于重庆市34个国家级气象站1965~2016年7~9月逐日降水资料,采用标准化降水指数、降水量距平百分率指标,分析重庆市伏秋旱的时空演变特征。利用Spearman等级相关系数法与逐步回归方法筛选与SPI序列相关性较强的气候因子。结果表明:7~9月伏秋连旱的频率为7.7%;7、8月伏旱同步的比例占15.4%;8、9月干旱同步的比例占13.5%,重庆市伏秋旱情况年际变化大。20世纪60~70年代,伏秋旱情况较严重;自20世纪80年代中后期起,旱涝交替出现;21世纪严重伏秋旱频发。从20世纪60年代以来,全市年平均总旱旬数从3.3旬增加至4.1旬,连旱旬数从2旬增加至2.5旬。在1965~2016年,重庆市西部多年平均总旱旬数为3.6旬,连旱旬数为2.2旬,相对较少。2006年特大旱灾之后,东南部和东北部伏秋旱程度轻,中部和西部程度严重。重庆市伏秋旱事件与环流、海温异常存在密切关系,主要影响因子包括:北半球副高脊线位置指数、北半球副高北界位置指数、NINO A区海表温度距平指数、黑潮区海温指数等。重庆市7月SPI与同年1月北半球副高脊线位置指数、9月SPI与同年4月NINO A区海表温度距平指数均呈负相关关系。研究成果可为保障重庆市水安全、实现水资源科学配置提供理论基础。

The mid summer and autumn droughts refers to droughts that occur in summer or autumn,which occur frequently in Chongqing and cause economic losses.Based on daily precipitation data of 34 national meteorological stations from July to September during 1965-2016 in Chongqing,the temporal and spatial variation of the mid summer and autumn droughts were analyzed by Standardized Precipitation Index(SPI)and precipitation anomaly percentage index(PA).By Spearman rank correlation method and stepwise regression method,factors with strong correlation were screened out from climate factors.The results showed that the frequency of continuous mid-summer and autumm droughts from July to September was 7.7%.The drought synchronization accounted for 15.4%in July-August and 13.5%in August-September.The drougnts varies greatly in Chongqing from 1960 s to 1970 s,the mid summer and autumn droughts was getting more serious;since the middle and late 1980 s,droughts and floods have appeared alternately;in the 21 st century,severe summer and autumn droughts occurred frequently.After the 1960 s,the annual average total number of drought xun(ten-days)increased from 3.3 to 4.1 xun,and the number of coutinuous drought xun increased from 2 to 2.5 xun.From 1965 to 2016,the annual average total number of drought xun in the western region was 3.6 xun,and the number of coutinuous drought xun was 2.2 xun,which was relatively small.After 2006,the mid summer and autumn drought was mild in the southeastern and northeastern regions,and severe in the middle and the western regions.The mid summer and autumn droughts in Chongqing are closely related to the circulation and SST anomalies.The main correlated factors include Northern Hemisphere subtropical high ridge position index,Northern Hemisphere subtropical high northern boundary position index,the NINO A SSTA index and the Kuroshio current SST index.The SPI of Chongqing in July was negatively correlated with the Northern Hemisphere subtropical high ridge position index in January of the same year;the SPI in September was negatively correlated with the NINO A SSTA in April of the same year.The research results can provide a theoretical basis for ensuring water security and realizing the scientific allocation of water resources in Chongqing.