The effect of moisture source and synoptic conditions on precipitation isotopes in arid central Asia

Abstract

The stable isotope composition of precipitation has been widely applied to trace moisture sources. In the westerly dominated areas of central Asia, the isotopic composition of precipitation significantly correlates with surface air temperature, and the temperature effect is widely accepted. However, the significance of isotopes in tracing water vapor source is not clear for this region, and a further investigation using event‐based observations is still needed. Based on a network around the Tianshan Mountains, the westerly regime of precipitation isotopes is investigated. Although the seasonality of precipitation isotopes for the northern and southern basins of the Tianshan Mountains is similar, the more arid climate and leeward landform of the southern basin lead to weak moisture transport and relatively enriched oxygen isotopes. Of the synoptic systems resulting in heavy precipitation, the central Asian vortex more commonly leads to depleted isotopic ratios in precipitation, which is related to the contribution of northerly moisture and/or surface moisture. The specific humidity‐adjusted Lagrangian diagnostic indicates that the heavy precipitation on the southern basin stations usually has relatively local moisture sources in this arid climate and that terrestrial moisture evaporated from Europe and central Asia, rather than marine moisture from the Atlantic Ocean, is more likely to be the direct moisture source. A sensitivity analysis for target height and adjusting threshold of specific humidity is also applied to the improved Lagrangian diagnostic. Overall, the findings were unaffected by different conditions, and the moisture was more likely to be locally sourced, as indicated by higher specific humidity thresholds.

Stable Isotopic Characteristics and Influencing Factors in Precipitation in the Monsoon Marginal Region of Northern China

“…This seasonal change is similar to that of temperature, reflecting continental climate characteristics [27]. Terrestrial moisture evaporated from Europe and central Asia may be the main moisture source around the Tianshan Mountains [28].…”

Nonmonsoon Precipitation Dominates Groundwater Recharge Beneath a Monsoon‐Affected Glacier in Tibetan Plateau

“…An interesting feature is found that the ice‐melt water is generally more enriched in heavy isotopes than the summer precipitation in the SETP, while it is inverse in the Tianshan Mountains. This is probably due to lack of monsoon sources for precipitation in the Tianshan Mountains (Kong & Pang, ; Li et al, ; Wang et al, , ), which is beyond the discussion of this work.…”

Water Source Signatures in the Spatial and Seasonal Isotope Variation of Chinese Tap Waters

“…Winter precipitation in this region is very limited, and amount‐weighted precipitation isotope ratios are higher than the tap water values on an annual basis (Figures a and b). Tap water in this region is also characterized by limited seasonal isotopic variability (Figure S5a), despite large variations in precipitation isotope ratios (Wang et al, ; Zhang & Wang, , ), leading to the largest observed seasonal offsets between tap water and precipitation (Figure a). This argues for a relatively weak interaction between local precipitation and surface water in the systems supplying the water, consistent with the dominant use of groundwater or water from river basins with a relatively long residence time.…”