【作者】 邓汗青；

【导师】 罗勇；

【作者基本信息】 南京信息工程大学 ， 气候系统与全球变化， 2013， 博士

【摘要】 长江流域降水异常对我国粮食生产和经济发展有着重要影响。本文利用了长江流域内21个气象站1880年-2011年季节降水量资料研究了春、夏季降水异常转换的时空特征。同时对各类异常转换事件的成因进行了分析,然后深入探讨了2011年长江流域所发生的“旱涝急转”事件。最后运用最新一代CMIP5模式资料预估未来2013年-2050年间长江流域春、夏季降水变化趋势。主要结论如下：(1)长江流域春、夏季降水量有着显著的年际和年代际变化特征,两者的变化不仅表现出一致性也具有相互独立性。在过去的132年中春、夏季降水持续偏少事件(旱-旱)最为普遍,平均每3年发生一次,而春季降水偏少而夏季偏多的演变事件(旱-涝)相对发生较少。从1880年代到2000年代,春、夏季降水持续偏多事件(涝-涝)发生频次呈现减少趋势,春、夏季降水持续偏少事件(旱-旱)则显著增加,而其余两类事件的线性变化不显著。(2)利用季节经验正交分解(S-EOF)对长江流域春、夏季降水量进行分解并得到前三个经验模态及其时间系数。第一模态所呈现出的是整个长江流域春、夏季降水量异常为一致性的演变,而最典型区域主要集中在长江中下游；第二模态反映了全流域春季降水负异常而夏季正异常的演变过程；第三模态则体现了春、夏季流域南北部降水异常相反特征的持续发展。(3)水汽输送、海温、500hPa位势高度场、东亚副热带西风急流和季风异常都对春、夏季降水量S-EOF演变模态有着不同作用。综合选取6个物理因子进行统计实验,结果表明春、夏季降水演变的第一、二模态主要与水汽输入量和季风的拟合效果较好。(4)2011年长江流域发生的“旱涝急转”表现为春季降水量负距平向6月正距平的转换,从空间上看“旱涝急转”主要发生在长江中下游地区。前期Nino3.4海温偏低、水汽输送偏弱、副高位置偏东、东亚副热带西风急流偏强以及异常垂直下沉运动导致了春季长江流域降水量偏少,而到了6月份水汽输送增加、副高位置偏西、东亚副热带西风急流偏南和异常垂直上升运动都有利于降水增加。(5) CMIP5多模式集合结果对长江流域春、夏季降水量变化及异常转换有一定模拟能力。未来2013年-2050年,在三种典型浓度路径下春季降水都有线性增加趋势,夏季降水量则无显著变化。在RCP2.6、RCP4.5和RCP8.5路径下2020年代(2013年-2030年)和2040年代(2031年-2050年)长江中下游地区春季降水都可能偏多。2020年代长江中游夏季降水量都将偏少,而在2040年代降水偏少的区域主要位于流域西北部。(6)2013年-2050年间,在RCP2.6和RCP4.5路径下春、夏季降水量持续偏多的转换可能将会频发,而在RCP8.5路径下长江流域除了春、夏季降水量持续偏多的异常转换外,春季降水量偏多而夏季偏少的转换可能也将较为普遍。更多还原

【Abstract】 The Yangtze River Basin covers national economic and culture centres which are especially vulnerable to the rainfall anomaly. Precipitation changes in spring (MAM) and summer (JJA) over the Yangtze River Basin during1880to2011were analyzed based on observation datasets from21gauge stations. The mechanisms were discussed by using the NCEP reanalysis datasets. Finally, the projected changes in precipitation were evaluated by using nine CMIP5datasets. The major conclusions are as follows:(1) Interannual and interdecadal changes in spring and summer precipitation occurred during1880to2011. The Dry-Dry patterns of seasonal evolution generally occurred and Dry-Wet patterns were rare occurrence over the past132years. Begining in1880s, the first species and third species has decreased and increased respectively, however the changes of other patterns were not obvious.(2) S-EOF analysis was employed to identify the major modes of seasonal precipitation evolution from spring to summer in the Yangtze River Basin, the first three modes were decomposition by S-EOF. The leading mode describes the spatial coincidence of seasonal variability from spring to summer. Almost the entire Yangtze River Basin has been dominated by a positive anomaly, especially in the middle and lower basins from spring to summer. The opposite precipitation anomaly between North and South appeared in the third mode whatever in spring or summer.(3) The first two S-EOF modes were affected by water vapor transport, sea surface temperature,500hPa geopotential height, extratropical westerly jet and monsoon. Six physical factors were selected to design statistical experimental. The result showed that the most significant factors were spring and summer monsoon index and input moisture.(4) A sudden turn from drought to flood resulted in enormous losses occurred in2011over the middle-lower part of the Yangtze River Basin. Persistent negative anomalies were identified during MAM. However, a significant transition was detected by the increasing Meiyu rainfall during the June. The water vapor fluxes, SSTA, extratropical westerly jet, monsoon, the corresponding location of the western Pacific subtropical high (WPSH) and vertical motion anomalies in spring and June were described and examined to investigate the mechanism of the sudden precipitation transition in2011. (5) The ensemble mean precipitation was relatively close to the observation in baseline.The time series of spring precipitation shows a significant positive linear trend in RCP2.6and RCP8.5. But no significant trend was found in RCP4.5. Compared with the baseline, spring precipitation will increase in the mid-low Northern Yangtze River Basin under each RCP. However a similar pattern shows that rainfall will decrease over the middle basin under each RCP in summer. A relatively higher anomaly over a wider area will occur in RCP8.5. In the2040s, the similar patterns are presented in spring and summer under each RCP. Summer rainfall in the middle basins and Northern basin will exhibit a negative anomaly in2020s and2040s under all RCPs respectively.(6) The Wet-Wet pattern will be common under RCP2.6and RCP4.5. The Wet-Wet and Wet-Dry patterns both will become more frequent under RCP8.5.更多还原