汉江流域夏季降水演变的水汽输送驱动机制

Mechanism of moisture transport associated with summer precipitation of the Hanjiang River Basin

为应对气候变化下愈加频繁和剧烈的干旱事件,保障跨流域调水工程水源及当地用水安全,亟需对汉江流域这一国家重要战略水源地的降水过程变化进行研究。汉江流域夏季降水占全年降水的40%~50%。本研究利用拉格朗日混合单粒子轨道模型对汉江流域1959—2022年夏季降水的水汽输送过程及其大气环流背景进行分析,以揭示汉江流域夏季降水变化的原因。研究发现,历时72 h以上降水占夏季总雨量的44.6%,在过去半个多世纪中其频次和雨量均呈现显著下降趋势,是汉江流域降水减少的主要原因。对水汽输送过程的模拟分析表明,中国南海、西太平洋、中国东部是流域夏季降水的水汽来源,贡献率分别为:34.7%、28.7%、27.2%。对比不同历时降水的水汽输送过程,发现降水历时越长,来自中国南海和西太平洋的水汽贡献率越高。尽管来自西太平洋的水汽呈现显著增加,但来自中国南海的水汽显著下降,使得72 h以上降水仍然呈现下降趋势。分析大尺度气候指数与各水汽输送路径贡献率的相关性,发现中国南海水汽贡献减小与西太平洋副热带高压面积、强度增加呈显著负相关。这证实了近年来西太副高的增强和扩张对汉江流域夏季降水减少起到促进作用。

In order to cope with the increasingly frequent and intense droughts under climate change,and to guarantee the water safety of water transfer projects and local water use,it is urgent to reveal the mechanisms of the changes in precipitation of the Hanjiang River Basin(HRB),which is a national strategic water source.Summer precipitation in the HRB accounts for 40-50%of the annual precipitation.In this study,the Hybrid Single-Particle Lagrangian Integrated Trajectory model was used to analyze the moisture transport of summer precipitation in the HRB and its atmospheric circulation background during 1959-2022.It was found that precipitation lasting over 72 hours accounted for 44.6%of the total summer rainfall,and both frequency and amount have shown significant downward trends,which is the main reason for the decrease in precipitation of the HRB.Simulation of the moisture transport process shows that the South China Sea(SCS),Western Pacific(WP),and Eastern China(EC)are the main sources of water vapor for summer precipitation in the basin,with contributions of 34.7%,28.7%,and 27.2%,respectively.Comparison of moisture transport processes for precipitation of different durations shows that the longer the precipitation duration,the higher the contribution of water vapor from SCS and WP.Although the moisture from WP shows a significant increase,the moisture from SCS decreases significantly so the precipitation over 72 hours still shows a decreasing trend.The negative correlation between the West Pacific Subtropical High index and the contribution of SCS to the precipitation in HRB partially confirms the contribution of the enhancement and expansion of the WPSH on the reduction of summer precipitation of HRB in recent years.