Amount and temperature effects responsible for precipitation isotope variation in the southern slope of Himalayas

Tek Bahadur Chhetri; TanDong Yao; LiDe Tian; XinPing Zhang

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Amount and temperature effects responsible for precipitation isotope variation in the southern slope of Himalayas

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Seasonal variation of stable isotopes in precipitation of Kathmandu Valley on the southern slope of Himalaya was carried out to understand the controlling mechanism of amount and temperature effect on the basis of one year stable isotope data from 2010 to 2011. Highly depleted isotope values in major rainy period are obtained just after the onset of precipitation in summer, which accounts for "amount effect" due to saturation isotopic compositions in high moisture condition, whereas, the higher values in winter are indicative to regional vapors (temperature effect) recycling of various sources. An abrupt depletion of isotope values in mid-June, indicates the onset date of monsoon precipitation, by the replacement of winter air mass with southern monsoon. Thus, precipitation isotopes are a tool revealing the onset date of summer monsoon and temporal features of variability, in local and regional monsoons precipitations. A comparison of long term monthly values of δ 18 O, temperature, and precipitation with GNIP δ 18 O data shows the temporal variations of stable isotopes are mostly controlled by amount and temperature effects. During summer monsoon, the amount effects are stronger for high values of precipitation (R=0.7) and altitude effect appears for low moisture in late rainy season, thus from December to June (winter to pre-monsoon) the controlling features of isotopes remains under the temperature effect. A temporal rate of temperature effect is derived as 0.04‰ per year which indicates a dry signal of atmospheric condition and a temperature relation δ 18 O=(0.371±0.08)T+(0.156±0.05) is obtained from this analysis. The meteoric water lines of Kathmandu before and after monsoon onset of 2011, are found as δD=(4.36±0.3)δ 18 O+(15.66±1.2) and δD=(6.91±0.2)δ 18 O (7.92±2.26) from lab samples result, and δD=9.2δ 18 O+11.725 and δD=8.53δ 18 O+16.65 from GNIP data, which lacks the consistency both for slopes and intercepts values for the study period. The mean lapse rate values of δ 18 O and δD from GNIP data are obtained as 0.002‰/m and 0.015 ‰/m, which indicate the altitudinal effects in regional precipitation of the southern slope of Himalayas. This study estimates new stable isotopes data in recent precipitation using simple methodology which can be important for regional precipitation monitoring systems, environmental change and paleo-climatic studies.

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《寒旱区科学（英文版）》 |2013年第2期|165-176|共12页
作者
Tek Bahadur Chhetri; TanDong Yao; LiDe Tian; XinPing Zhang;
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Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China;

University of Chinese Academy of Sciences, Beijing 100049, China;

Central Dept.of Hydrology and Meteorology, Tribhuvan University, TU, Kathmandu, Nepal;

Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China;

Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China;

College of Resources and Environmental Sciences, Hunan Normal University, Changsha, Hunan 410081, China;

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Amount and temperature effects responsible for precipitation isotope variation in the southern slope of Himalayas

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