基于拉格朗日方法评估青藏高原若尔盖地区水汽输送特征

The Characteristics of Water Vapor Transport Based on Lagrangian Method in the Zoige,Qinghai-Xizang Plateau

干旱指数一直以来是评估一个地区地表干湿状态的有效标准。为了认识青藏高原若尔盖地区在极端干旱和湿润条件下的水汽空间分布格局,本文基于地面观测资料计算月尺度的标准化降水蒸散指数,提取2000-2017年青藏高原若尔盖地区的极端干旱和湿润状况,利用拉格朗日后向轨迹模型模拟该地区极端干湿条件下的水汽输送路径,并评估潜在水汽源地的位置以及对研究区水汽输送的贡献率。结果表明:湿润时期主要的水汽输送路径是受到西南季风影响的南支输送路径,该路径起始于阿拉伯海、孟加拉湾,从西-南方向进入青藏高原,再到达若尔盖地区,而干旱时期的水汽输送路径主要受到西风带的影响,占主导地位的路径则是起始于北美、北大西洋的自西向东,由亚欧大陆到达青藏高原北部。主要的水汽源地出现在青藏高原、四川盆地、孟加拉湾、阿拉伯海等区域,但受到不同时期的水汽输送路径影响,各水汽源地在不同时期表现出了不同特征,湿润时期主要的水汽源地出现在青藏高原南部(贡献率为35.98%),而干旱时期主要的水汽源地则出现在青藏高原北部(贡献率为28.35%),此外来自阿拉伯海以及孟加拉湾等地的水汽源地在湿润时期贡献率更高,而研究区域本身以及四川区域的水汽贡献率则在干旱时期更高。分析结果将有助于理解极端干湿状态的形成机制,进而加深对旱涝灾害机制的理解。

The drought index has always been a practical standard for assessing a specific region’s dry and wet state.In order to better understand the spatial distribution pattern of water vapor transport in the Zoige region of the Qinghai-Xizang Plateau under extreme dry and wet conditions,this paper calculates the monthly standardized precipitation evapotranspiration index based on the ground observation data.It extracts the extreme drought and wet conditions in the Zoige region of the Qinghai-Xizang Plateau from 2000 to 2017.The Lagrangian backward trajectory model is used to simulate the water vapor transport path under extreme dry and wet conditions and evaluate the location of potential evapotranspiration water vapor sources and their contributions to the water vapor transport in the study area.The results show that the main water vapor transport path is concentrated in the south branch transport path affected by the southwest monsoon during the wet period.The route originates from the Arabian Sea and the Bay of Bengal and finally arrives at the Zoige from the western and southern flank of the Qinghai-Xizang Plateau.Moreover,the water vapor transport pathway during the drought period is mainly affected by the westerlies.The dominant path starts from North America and the North Atlantic,spreads from west to east,the mid-latitude Eurasian continent,and finally reaches the north of the Qinghai-Xizang Plateau.The main water vapor sources appeared in the Qinghai-Xizang Plateau,Sichuan Basin,Bay of Bengal,Arabian Sea,and other regions.Affected by the water vapor transmission path in different periods,these water vapor sources show different characteristics.In the wet period,the water vapor source is mainly distributed around the south of the Qinghai-Xizang Plateau(the contribution rate is 35.98%).In contrast,the primary water vapor source during the drought period appears in the northern Qinghai-Xizang Plateau(the contribution rate is 28.35%).In addition,the contribution rate of water vapor sources from the Arabian Sea and the Bay of Bengal is higher in the wet period.In contrast,the contribution rate of water vapor in the local Zoige area and Sichuan is higher in the drought period.The analysis results will help to understand the formation mechanism of water vapor during extreme drought and wet states,how the water vapor sources work,and the contribution rate of the water vapor sources.This research can deepen the understanding of the mechanism of drought and flood disasters.