Abstract

Precipitation stable isotopes (²H and ¹⁸O) are adequately understood on their climate controls in the Tibetan Plateau, especially the north of Himalayas via about 30 years’ studies. However, knowledge of controls on precipitation stable isotopes in Nepal (the south of Himalayas), is still far from sufficient. This study described the intra-seasonal and annual variations of precipitation stable isotopes at Kathmandu, Nepal from 10 May 2016 to 21 September 2018 and analysed the possible controls on precipitation stable isotopes. The enriched δD and δ¹⁸O values were identified during non-monsoon season and depleted values were found during monsoon season, showing remarkable intra-seasonal characteristics of monsoon influence. The local meteoric water line suggested a strong influence of evaporation during rainfall in non-monsoon season and significant impact of non-equilibrium processes on precipitation during monsoon season. Temperature–δ¹⁸O exhibited negative correlation for overall samples and showed no significant correlation in seasonal scales, which was attributed to the influence of monsoon moisture. The positive correlation was observed between δ¹⁸O and outgoing longwave radiation (OLR) in monsoon season, suggesting the significant impact of convective activity on temporal variations of precipitation stable isotopes. During April, and May of 2016 and 2017, variation of precipitation stable isotopes are probably related with the mixing of multi-moisture combined with the westerlies transport. Our study suggested that the moisture transport processes are the main controls of precipitation stable isotopes at Kathmandu.

摘要

经过大约30年的研究，在青藏高原，尤其是喜马拉雅山北部，人们对降水稳定同位素（² H和¹⁸ O）的气候控制有了充分的了解。但是，对尼泊尔（喜马拉雅山南部）的降水稳定同位素的控制知识还远远不够。这项研究描述了2016年5月10日至2018年9月21日尼泊尔加德满都的降水稳定同位素的季节内和年度变化，并分析了对降水稳定同位素的可能控制。富集δD和δ ¹⁸在非季风季节确定了O值，在季风季节发现了O值，这表明季风影响具有明显的季节内特征。当地的大气水线表明在非季风季节降雨期间蒸发的影响很大，而在季风季节非平衡过程对降水的影响很大。温度-δ ¹⁸ ö展示的总体样本的负相关和季节性尺度，这是归因于季风湿气的影响显示没有显著相关性。δ之间观察到的正相关¹⁸O和季风季节的长波辐射（OLR），表明对流活动对降水稳定同位素随时间变化的重大影响。在2016年和2017年的4月，5月和5月期间，降水稳定同位素的变化可能与多水分的混合以及西风的运移有关。我们的研究表明，水分输送过程是加德满都降水稳定同位素的主要控制因素。