Water isotope-based hydrological and paleoaltimetry studies in high mountain areas are generally done using the isotopic composition of river discharge. However, rivers capture a basin averaged signal of regional precipitation and are less likely to register the meteorological processes intrinsic to distinct hydrological fractions at different altitudes. This has been observed in the Khumbu (Mt. Everest) Himalayan watersheds of Dudh Kosi Basin (DKB), where the δ¹⁸O values of snowpack and stream water vary non-uniformly with altitude while the δ¹⁸O values of river water show a uniform relationship. Snow exhibits the highest (+0.9 to −4.4‰/100 m) isotopic lapse rate (ILR), followed by streams (+0.2 to −0.4‰/100 m) and rivers (−0.05‰/100 m). Sublimation, catchment vegetation, diurnal temperature, cloud type, and insolation play a significant role in controlling the isotopic composition of snowpack and stream water. Similarly, the isotopic composition of small streams disproportionately represents the meteoric water composition of an area, as rainfall immediately joins the stream-runoff while the snow melts gradually around the year. To map the isotopic heterogeneity in DKB surface waters, we have modeled the isoscape for surface runoff using the isotopic composition of snow and stream water, and remotely sensed parameters. Accordingly, we simulate the isoscapes for snow and stream-runoff via multi-regression models which extrapolate the observed data as a function of the controlling factors. The amount-weighted summation of both the isoscapes (relative contribution (%) *δ¹⁸O value) constitutes the hydropool. The hydropool model incorporates spatiotemporal variation in ILR computed from the δ¹⁸O values of surface runoff.

中文翻译：

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高山流域地表径流的等值景：气象水表征的替代模型及其影响

高山地区基于水同位素的水文和古高度测量研究通常使用河流排放的同位素组成进行。然而，河流捕获区域降水的流域平均信号，不太可能记录不同海拔不同水文部分固有的气象过程。这已经在 Dudh Kosi 盆地 (DKB) 的 Khumbu（珠穆朗玛峰）喜马拉雅流域观察到，其中积雪和溪流水的 δ ¹⁸ O 值随高度不均匀变化，而 δ ¹⁸河水的 O 值表现出一致的关系。雪的同位素递减率 (ILR) 最高 (+0.9 至 -4.4‰/100 m)，其次是溪流 (+0.2 至 -0.4‰/100 m) 和河流 (-0.05‰/100 m)。升华、集水植被、昼夜温度、云类型和日照在控制积雪和河流水的同位素组成方面起着重要作用。同样，小溪流的同位素组成不成比例地代表了一个地区的大气水组成，因为降雨会立即加入溪流径流，而雪在一年中逐渐融化。为了绘制 DKB 地表水中的同位素异质性，我们使用雪和溪流水的同位素组成以及遥感参数对地表径流的等值线进行了建模。因此，我们通过多重回归模型模拟雪和河流径流的等值景观，该模型将观测数据外推为控制因素的函数。两个等值景的数量加权总和（相对贡献 (%) *δ¹⁸ O值）构成水池。水池模型结合了根据地表径流的 δ ¹⁸ O 值计算出的 ILR 的时空变化。