The extreme changes in autumn rain have significant impacts on the ecological environment of Weihe River basin. Based on 117 autumn rain samples and corresponding meteorological data from 2015 to 2021 at Yangling located in the middle of Weihe River basin, we investigated the stable hydrogen and oxygen isotope composition and water vapor sources of precipitation. The results showed that, (1) extreme changes in autumn rainfall in the study area occurred frequently in recent years, which could be divided into extreme-high autumn precipitation year (HAP, 2021), general autumn precipitation year (GAP, 2015-2017, 2019-2020) and extreme-low autumn precipitation year (LAP, 2018) based on the autumn rain index (ARI); (2) the stable isotopes of different types of precipitation differed significantly, with a pattern of LAP>GAP>HAP for both δ2H and δ18O values. the variations of d-excess values and the slopes and intercepts of the meteoric water lines of autumn rain showed opposite trends. The main factor controlling autumn rain anomaly was not the local meteorological parameters, but the El Nino-Southern Oscillation and the Indian Ocean dipole events, which could explain 99% and 93% of the autumn rain isotopic variations, respectively. These coupling phenomena affected water vapor transport intensity of the marine air mass to the northwest inland, which determined autumn rainfall amount and the stable hydrogen-oxygen isotope composition. Our results would be helpful for improving the understanding of autumn rain anomalies in West China, and provide basic data and theoretical support for regional hydrological model building, would thereby better serve water resources management and disaster prevention and reduction.
秋雨极端变化对渭河流域生态环境影响巨大。本研究根据2015—2021年在渭河流域腹地杨凌区采集的117个秋季降水样本和同期相关气象资料,开展秋雨异常氢氧稳定同位素组成及其水汽来源的研究。结果表明: 1)近年来研究区秋雨极端变化频繁,根据秋雨指数(ARI)可分为秋季极端多雨年(HAP,2021年)、普通降雨年(GAP,2015—2017, 2019—2020年)和极端少雨年(LAP,2018年);2)不同类型秋雨氢氧稳定同位素组成差异明显,其中,δ2H、δ18O值呈现出LAP年>GAP年>HAP年的变化趋势,而d-excess值和秋雨降水线斜率、截距值的变化趋势与之相反。进一步分析不同类型秋雨同位素的影响因素和水汽来源发现,出现秋雨异常的主要原因并非当地气象要素,而可能是厄尔尼诺-南方涛动事件和印度洋偶极子事件,其分别解释了99%和93%的秋雨同位素异常变化。这些海气耦合现象影响海洋性气团水汽向西北内陆的输送强度,进而决定了秋雨雨量和氢氧稳定同位素组成。本研究结果有助于提高对华西秋雨异常的认识,为区域水文模型的构建提供了基础资料和理论支撑,可以更好地服务于水资源管理决策和防灾减灾。.
Keywords: Weihe River basin; extreme autumn precipitation; stable isotopes of hydrogen and oxygen; water vapor source.