西南地区不同地形降水稳定同位素特征及其水汽来源

为阐明西南地区不同地形对于降水稳定同位素的影响以及各个水汽团在地理上的分界线，选取四川盆地、云贵高原、青藏高原东部及横断山脉3个地区共10个研究点作为本次研究的对象，分析了西南地区大气降水中δD、δ18O的时空变化特征，并初步建立了3个地区大气降水线，探讨了降水稳定同位素与温度、降水量及水汽来源之间的关系，并利用HYSPLIT4.9模型分析追踪冬夏半年降水事件的水汽来源及运移路径。结果表明：西南地区降水稳定同位素存在显著的高程效应；δ18O=-0.0028H-3.93,R=0.89，降水中δ18Ｏ和δＤ值表现出由四川盆地-云贵高原-青藏高原东部与横断山脉地区逐渐贫化的趋势，季节变化规律特征为冬半年整体偏重，而夏半年整体偏轻。同时西南地区除昆明与成都地区外，d值整体上表现出夏低冬高的特征，符合我国季风降水影响区域的特点。3处地区大气降水线（LMWL）与全球大气降水线（GMWL）相比，四川盆地、青藏高原东部及横断山脉地区斜率与截距明显偏小，而云贵高原斜率与截距偏大，其主要与水汽凝结时温度、蒸发条件、水汽来源以及输送方式有关。温度效应和降水量效应在不同地区主导性存在差异，四川盆地地区、云贵高原地区、青藏高原东部以及横断山脉地区整体上不存在温度效应，存在显著降水量效应。西南各地区主导型水汽团也存在差异性，通过对不同地区冬夏季风期间主导型水汽团初步分析，受单一性水汽团影响的区域主要分布于西南部与东北部，而受多种水汽团影响的区域主要分布于西北部与东南部；贵阳-安顺一线处于西太平洋水汽团与孟加拉湾水汽团交界处，成都-卧龙-黄龙一线处于西太平洋水汽团与西风带水汽团的交界处。 关键词： 大气降水；稳定同位素；水汽来源；不同地形；西南地区

Characteristics of the Stable Isotopes in Precipitation and the Source of Water Vapor in Different Terrain in the Southwest Region

In order to clarify the influence of different terrain on the stable isotope of precipitation in the southwest and the geographical boundary of each water vapor mass, a total of 10 research sites in Sichuan Basin, Yunnan-Guizhou Plateau, the eastern of Qinghai-Tibet Plateau and Hengduan Mountains were selected as the study area, analyzing the spatiotemporal variations of δD and δ18 O in precipitation in southwest China and initially establishing three regional meteoric water line. Relations between δ18 O in precipitation and air temperature, amount and moisture sources were discussed, and HYSPLIT4.9 model was used to analyze and trace water source and migration path of precipitation events in summer and winter half year. The results show that there are significant elevation effects of precipitation stable isotopes in the southwest region, that as δ18 O=-0.002 8H-3.93 and R=0.89, values of δ18 O and δD in the precipitation are gradually depleted from the Sichuan Basin, the Yunnan-Guizhou Plateau, the eastern part of the Qinghai-Tibet Plateau and the Hengduan Mountains, and that the seasonal variation characteristics of the winter half year are positive on a whole, while those of the summer half year are overall negative. In addition to Kunming and Chengdu area, the value of d in the southwest region shows the trend of being low in summer and being high in winter, which is in line with the characteristics of the region influenced by monsoon precipitation in China. Compared with the global meteoric water line (GMWL), slopes and intercepts of regional atmospheric precipitation lines(LMWL) in the Sichuan Basin, the eastern Qinghai-Tibet Plateau and the Hengduan Mountains are apparently smaller, while those in the Yunnan-Guizhou Plateau are larger, which is mainly relative with temperature of water vapor condensation and evaporation, water vapor sources and transmission ways. Temperature effect and precipitation effect are different in different regions—there is no temperature effect in the Sichuan Basin, the Yunnan-Guizhou Plateau, the eastern Qinghai-Xizang Plateau and the Hengduan Mountains, but a remarkable precipitation effect. There are also differences in dominant water vapor mass in different regions of Southwest China. Based on the preliminary analysis of the dominant water vapor during winter and summer monsoon season in different regions, conclusions can be draw that the areas affected by single water vapor mass are mainly distributed in the southwest and northeast, while the regions influenced by multiple water vapor mass are primarily distributed in the northeast and southeast, that the Guiyang-Anshun line is on the border of the Western Pacific water vapor mass and the Bay of Bengal water vapor mass, and that Chengdu-Wolong-Huanglong line is on the border of the Western Pacific water vapor mass and the Westerly water vapor.