华北北纬38°带极端强降水氢氧稳定同位素特征与水汽来源的关系

The relationship between characteristics of stable isotopes and moisture sources of extreme precipitation in the transection of 38° north latitude in North China

华北北纬38°带是华北地区的重要农业区,降水是区域地下水的主要补给源。近年来,极端强降水频率增加改变了地下水补给方式,明确极端强降水氢氧稳定同位素特征及其水汽来源对于深入认识区域水循环特征具有重要意义。本研究基于2016年1月至2021年12月华北北纬38°带的1个山区站点(太行山站)和2个平原区站点(栾城站和南皮站)降水样品采集,采用相关分析和HYSPLIT模型,揭示了研究区极端强降水δ2H和δ18O的时空分布特征与水汽来源的关系。结果表明:降水氢氧稳定同位素呈现丰水年贫化的年际特征,雨季富集、旱季贫化的季节性变化特征,极端强降水同位素最为贫化(-105.7‰~-39.1‰,-14.6‰~-5.7‰)。大气降水同位素关系表明位于山前平原的栾城站斜率和截距最小,蒸发作用最强。HYSPLIT模型结果表明,太行山站极端强降水水汽主要来自于东南季风和西南季风水汽,而栾城站和南皮站极端强降水水汽主要来自于西风水汽和东南季风水汽,西南季风水汽比例增加(16.67%~58.33%)是导致山区极端强降水同位素比平原区贫化的主要原因。水汽来源的差异导致研究区2021年“7·21”极端强降水事件δ18O值高于2016年“7·19”极端强降水事件。上述认识可为华北北纬38°带大气环流和水文循环过程研究提供基础。

The transection of 38°north latitude in North China is an important agricultural zone,and precipitation is the main source of groundwater supply in the region.In recent years,the increasing frequency of extreme precipitation has changed the way groundwater is replenished.This study is based on the collection of precipitation samples from one mountainous station(Taihangshan)and two plain stations(Luancheng and Nanpi)in the transection of 38°north latitude in North China from January 2016 to December 2021.Correlation analysis and HYSPLIT model were used to reveal the relationship between theδ2H andδ18O of the extreme heavy precipitation in the study area and spatiotemporal distribution characteristics and the moisture source.The results show that the stable isotopes of hydrogen and oxygen in precipitation show a trend of depletion between years in high water years.During the year,they show a trend of enrichment in the rainy season and depletion in the dry season,with extreme precipitation isotopes being the most depleted(-105.7‰to-39.1‰,and-14.6‰to-5.7‰,respectively).The isotope relationship of atmospheric precipitation indicates that Luancheng Station located in the piedmont plain has the smallest slope and intercept,and the strongest evaporation.The results of the HYSPLIT model indicate that the extreme heavy precipitation water vapor at Taihangshan Station mainly comes from the southeast monsoon water vapor and southwest monsoon water vapor,while that at Luancheng and Nanpi stations mainly comes from the westerly water vapor and southeast monsoon water vapor.The increase in the proportion of southwest monsoon water vapor(16.67%-58.33%)is the main reason for the isotope depletion of extreme heavy precipitation in mountainous areas compared to plain areas.The difference in moisture sources is the main reason why theδ18O value of the extreme heavy rainfall event on July 21,2021 in the study area is higher than that of the precipitation event on July 19,2016.The above understanding can provide a basis for the study of atmospheric circulation and hydrological cycle processes in the transection of 38°north latitude in North China.