CMIP5模式对未来30 a新疆夏季降水的预估

摘要

选用参与气候变化政府间合作委员会(IPCC)第5次评估报告的25个气候耦合模式(CMIP5),基于GPCP(Global Precipitation Climatology Project)降水资料,采用多种统计方法,综合评估模式历史试验对1979—2005年新疆夏季降水的模拟能力,优选出模拟性能较好的模式,进而利用其RCP8.5排放路径下的模拟结果来预估未来30 a(2021—2050年)新疆夏季降水的变化.从气候平均场和年际变率来看,25个CMIP5模式的模拟性能差异显著,部分模式可模拟出新疆夏季降水的主要空间分布特征,如伊犁河谷地区的降水中心以及南疆和东疆地区的少雨区.从优选出的9个模式的集合平均结果来看,对南疆西部山区与昆仑山北侧地区降水强度和范围模拟偏强,对年际变率的模拟偏弱,但其降水的空间分布与观测比较一致,可较准确地捕捉到高、低值中心,空间相关性也较好.因此,利用该集合平均结果对未来新疆降水进行预估是可信的.预估结果表明:(1)未来30 a北疆大部分地区和东疆部分地区夏季降水略微减少,伊犁河谷和南疆大部分地区显著增多,且增幅中心出现在南疆西部和昆仑山北侧地区;(2)山区年际变率较其他地区明显,且伊犁河谷、南疆西部和昆仑山北侧地区的年际变率呈现逐渐增大趋势;(3)降水变化与500 hPa环流配置异常密切相关,北疆地区偏南气流加强,表现为反气旋性环流,南疆地区偏东气流加强,表现为气旋性环流,因而导致未来新疆地区夏季降水南增北减.%Based on the outputs of historical and representative concentration pathway (RCP8.5) experiments produced by 25 models from phase 5 of the Coupled Model Intercomparison project (CMIP5), using the Global Precipitation Climatology Project (GPCP) dataset and several statistical methods, the performances in simulating the annual summer rainfall during 1979—2005 have been assessed, according to which, some preferable models among them has being identified. and projected changes in summer rainfall over Xinjiang of northwestern China in the next 30 a (2021—2050) have been further estimated. In terms of climatic mean and inter-annual standard deviation (ISD), there are notable differences among the 25 CMIP5 models, and part of them can well capture the main spatial patterns of summer rainfall over Xinjiang, such as the precipitation center over the Ili River Valley and shadows over the southern and eastern Xinjiang. Due to the 9 selected models' ensemble outputs, the spatial distribution of precipitation is identical to the observation. However, the simulated intensity and regions are overestimated while the ISD are underestimated over the west of southern Xinjiang and northern Kunlun Mountains. In the next 30 years, the summer rainfall decreases slightly over most of the northern Xinjiang and part of the eastern Xinjiang while increases significantly over the Ili River Valley and most of the southern Xinjiang with maximum centers located in the west of southern Xinjiang and northern Kunlun Mountains. The ISD is more remarkable in the mountains than other regions, and shows a gradually increasing trend over the Ili River Valley, as well as the west of the southern Xinjiang and northern Kunlun Mountains. Further analysis shows that the precipitation changes are closely related to the anomalous circulation configuration at 500 hPa. Southerly winds intensify and maintain an anticyclonic circulation over the northern Xinjiang while easterly winds and a cyclonic circulation over southern Xinjiang, which results in the increase of summer precipitation over the southern Xinjiang and decrease over the northern Xinjiang.