02 Nov 2023
 | 02 Nov 2023
Status: this preprint is currently under review for the journal HESS.

Altitudinal Control of Isotopic Composition and Application in Understanding Hydrologic Processes in the mid Merced River Catchment, Sierra Nevada, California, USA

Fengjing Liu, Martha H. Conklin, and Glenn D. Shaw

Abstract. Mountain snowpack has been declining and more precipitation has fallen as rainfall than snowfall, particularly in the US West. Isotopic composition in stream water, springs, groundwater, and precipitation was examined to understand the impact of declining snowpack on hydrologic processes in the mid Merced River catchment (1,873 km2), Sierra Nevada, California, USA. Mean isotopic values in small tributaries (catchment area < 122 km2), rock glacier outflows and groundwater from 2005–2008 were strongly correlated with mean catchment elevation (R2 = 0.96 for δ2H, n = 16, p < 0.001), with an average isotopic lapse rate of -1.9 ‰/100 m for δ2H and -0.22 ‰/100 m for δ18O in meteoric water. The lapse rate did not change much over seasons and was not strongly affected by isotopic fractionation. A catchment-characteristic isotopic value was thus established for each sub-catchment based on the relation between isotopic composition and the mean catchment elevation to elucidate hydrometeorologic and hydrologic processes. Compared to Tenaya Creek without water falls, flow and flow duration of Yosemite Creek are much more sensitive to temperature increase due to a strong evaporation effect caused by waterfalls, suggesting possible prolonged dry-up period of Yosemite Falls in the future. Groundwater in the Yosemite Valley (~900–1,200 m) was recharged primarily from the upper snow-rain transition zone (2,000–2,500 m), suggesting its strong vulnerability to shift in snow-rain ratio. The information gained from this study helps advance our understanding of hydrologic responses to climate change in snowmelt-fed river systems.

Fengjing Liu et al.

Status: open (until 28 Dec 2023)

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Fengjing Liu et al.

Fengjing Liu et al.


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Short summary
Mountain snowpack has been declining and more precipitation falls as rain than snow. Using stable isotopes, we found flows and flow duration in Yosemite Creek are most sensitive to climate warming due to strong evaporation of waterfalls, potentially lengthening the dry-up period of water falls in summer and negatively affecting tourism. Groundwater recharge in Yosemite Valley is primarily from the upper snow-rain transition (2,000–2,500m) and very vulnerable to shift in the snow-rain ratio.