摘要:基于台站资料和三套格点化降水资料，分析了21世纪初澜沧江流域夏季降水的年代际变化特征，并着重研究了其在不同月份的特点以及可能带来的旱涝风险。分析结果发现：澜沧江流域夏季降水发生了显著的年代际变化，在2002年前后，澜沧江流域夏季降水量经历了由多到少的年代际突变，且该突变主要发生在流域的中、下游。同时，在夏季的不同月份，降水的年代际变化也具有不同的特点，主要表现为：初夏（6月）降水量明显减少，而盛夏（7月）降水略有增加，且7月降水呈现集中的趋势。夏季降水量在时间分布上的变化使得澜沧江流域中、下游湿季明显缩短，进而对流域旱涝灾害产生显著的影响，主要表现为：使流域6月干旱频率增加，初夏干旱风险加大，7月极端强降水的发生频率增加，盛夏洪涝风险加大。进一步对突变前、后的水平环流场进行对比分析发现：2002年以后，澜沧江流域6月对流层低层有偏北风异常，不利于西南季风的向北推进，对流层高层有辐合异常，不利于降水的发生。在孟加拉湾地区对流层低层有明显的偏东北风异常，高层有偏西风异常，表明孟加拉湾季风偏弱，不利于印度洋和孟加拉湾向流域的水汽输送，不利于降水的形成。在这样的高、低层异常环流系统的配合下，2002年以后6月降水量显著减少。
关键词:澜沧江流域/
夏季降水/
突变/
时空变化特征
Abstract:In the early 21st century, the Lancang River Basin (LCRB) experienced an abrupt decrease in summer precipitation. Based on this conclusion, rainfall spatiotemporal variation characteristics and their effects on the frequency of droughts and floods were analyzed. The main results are as follows: The significant rainfall decreasing trend mainly occurred in June over the middle and low reaches of the LCRB, while the weak opposite trend mainly occurred in July over the middle and low reaches of the LCRB. These variations in characteristics led to the shortening of the LCRB wet period, which further contributed to an increase in droughts in June and the occurrence of heavy rain in July. The facts above indicate that in recent decades, the LCRB has experienced a notable increase in the risks of droughts in presummer and floods in midsummer. A further study of large-scale atmospheric circulation variation possibly associated with the remarkable rainfall decrease in June indicated that northerly anomalies existed over the lower troposphere of the LCRB, which hindered water vapor transport from the Indian Ocean and the Bay of Bengal (BOB). Moreover, cyclone anomalies in the higher troposphere of the LCRB formed an anomalous convergence, which was detrimental to the occurrence of rain. In addition, obvious northerly and westerly anomalies were present in the low and high troposphere over the BOB, respectively, indicating the monsoon in the BOB was weak, which hindered water vapor transport from the Indian Ocean and BOB as well. Due to such large-scale atmospheric circulation anomalies, the LCRB June rainfall has decreased significantly since 2002.
Key words:Lancang River Basin/
Summer precipitation/
Abrupt change/
Spatiotemporal variation characteristic
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