The Linkage between Two Types of El Niño Events and Summer Streamflow over the Yellow and Yangtze River Basins
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It is generally agreed that El Niño can be classified into East Pacific (EP) and Central Pacific (CP) types. Nevertheless, little is known about the relationship between these two types of El Niño and land surface climate elements. This study investigates the linkage between EP/CP El Niño and summer streamflow over the Yellow and Yangtze River basins and their possible mechanisms. Over the Yellow River basin, the anomalous streamflow always manifests as positive (negative) in EP (CP) years, with a correlation coefficient of 0.39 (−0.37); while over the Yangtze River basin, the anomalous streamflow shows as positive in both EP and CP years, with correlation coefficients of 0.72 and 0.48, respectively. Analyses of the surface hydrological cycle indicate that the streamflow is more influenced by local evapotranspiration (ET) than precipitation over the Yellow River basin, while it is dominantly affected by precipitation over the Yangtze River basin. The different features over these two river basins can be explained by the anomalous atmospheric circulation, which is cyclonic (anticyclonic) north (south) of 30°N over East Asia. EP years are dominated by two anticyclones, which bring strong water vapor convergence and induce more precipitation but less ET, and subsequently increase streamflow and flooding risks. In CP years, especially over the Yellow River basin, two cyclones dominate and lead to water vapor divergence and reduce moisture arriving. Meanwhile, the ET enhances mainly due to local high surface air temperature, which further evaporates water from the soil. As a result, the streamflow decreases, which will then increase the drought risk.
Key wordssummer streamflow EP El Niño CP El Niño Yellow River basin Yangtze River basin
本文研究分析了 EP/CP El Niño 对长江、 黄河流域的夏季径流的影响及其可能机制. 在黄河流域地区, 夏季径流的异常值在 EP (CP) 年表现为正 (负) 值, 相关系数为 0.39 (−0.37); 长江流域夏季径流的异常值在 EP 和 CP 年中均呈正值, 相关系数分别为 0.72 和 0.48. 分析表明, 在黄河流域地区, 径流量受到蒸发的影响大于降水影响, 而长江流域地区主要受降水影响. 这两片流域不同的陆表水文循环特征可以从东亚上空 30 °N 以北 (南) 的气旋 (反气旋) 的异常环流变化来解释. EP 年间, 东亚上空 30°N 以南的反气旋增强且出现两个反气旋中心, 使得该地区有强烈的水汽辐合, 导致降水增加、 蒸散发减少, 进而增加了径流量、 增大了洪涝灾害风险. CP 年间, 30 °N 以北的气旋增强且出现两个气旋中心, 导致东亚上空水汽辐散、 水汽输送减弱, 降水减少, 同时蒸散发增强, 尤其是在黄河流域, 这进一步减少了局地水汽, 使该流域的径流量减少、 干旱灾害风险增大.
关键词夏季径流 EP El Niño CP El Niño 黄河流域 长江流域
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This work was supported by the Key Project of the Ministry of Science and Technology of China (Grant No. 2016YFA0602401) and the National Natural Science Foundation of China (Grant No. 41875106). The authors would like to acknowledge the Data Center for Resources and Environmental Sciences, Chinese Academy of Sciences, for providing the China River Valley datasets, which are available for free at their website (http://www.resdc.cn). Other datasets used in this study have been acknowledged in the paper.
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