Volume 34, Issue 25 pp. 4794-4813
USING WATER AGE TO EXPLORE HYDROLOGICAL PROCESSES IN CONTRASTING ENVIRONMENTS

Seasonal snow cover decreases young water fractions in high Alpine catchments

Natalie Ceperley

Corresponding Author

Natalie Ceperley

Institute of Earth Surface Dynamics, Faculty of Geosciences and Environment, University of Lausanne, Lausanne, Switzerland

Institute of Geography, Faculty of Science, University of Bern, Bern, Switzerland

Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland

Correspondence

Natalie Ceperley, Institute of Geography, University of Bern Hallerstrasse 12, 3012 Bern, Switzerland.

Email: [email protected]

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Giulia Zuecco

Giulia Zuecco

Department of Land, Environment, Agriculture and Forestry, University of Padova, Legnaro, Italy

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Harsh Beria

Harsh Beria

Institute of Earth Surface Dynamics, Faculty of Geosciences and Environment, University of Lausanne, Lausanne, Switzerland

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Luca Carturan

Luca Carturan

Department of Land, Environment, Agriculture and Forestry, University of Padova, Legnaro, Italy

Department of Geosciences, University of Padova, Padova, Italy

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Anthony Michelon

Anthony Michelon

Institute of Earth Surface Dynamics, Faculty of Geosciences and Environment, University of Lausanne, Lausanne, Switzerland

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Daniele Penna

Daniele Penna

Department of Agriculture, Food, Environment and Forestry, University of Florence, Florence, Italy

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Joshua Larsen

Joshua Larsen

Institute of Earth Surface Dynamics, Faculty of Geosciences and Environment, University of Lausanne, Lausanne, Switzerland

School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK

The Birmingham Institute of Forest Research (BIFoR), University of Birmingham, Birmingham, UK

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Bettina Schaefli

Bettina Schaefli

Institute of Earth Surface Dynamics, Faculty of Geosciences and Environment, University of Lausanne, Lausanne, Switzerland

Institute of Geography, Faculty of Science, University of Bern, Bern, Switzerland

Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland

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First published: 11 October 2020
Citations: 24

Funding information: Fondazione Cassa di Risparmio di Padova e Rovigo, Grant/Award Number: Bando Starting Grants 2015; Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, Grant/Award Number: PP00P2_157611; Università degli Studi di Padova, Grant/Award Number: DOR2019

Abstract

Estimation of young water fractions (Fyw), defined as the fraction of water in a stream younger than approximately 2–3 months, provides key information for water resource management in catchments where runoff is dominated by snowmelt. Knowing the average dependence of summer flow on winter precipitation is an essential context for comparing regional drought severity and provides the hydrological template for downstream water users and ecosystems. However, Fyw estimation based on seasonal signals of stable isotopes of oxygen and hydrogen has not yet explicitly addressed how to parsimoniously include the seasonal shift of water input from snow. Using experimental data from three high-elevation, Alpine catchments (one dominated by glacier and two by snow), we propose a framework to explicitly include the delays induced by snow storage into estimates of Fyw. Scrutinizing the key methodological choices when estimating Fyw from isotope data, we find that the methods used to construct precipitation input signals from sparse isotope samples can significantly impact Fyw. Given this sensitivity, our revised procedure estimates a distribution of Fyw values that incorporates a wide range of possible methodological choices and their uncertainties; it furthermore compares the commonly used amplitude ratio approach to a direct convolution approach, which circumvents the assumption that the isotopic signals have a sine curve shape, an assumption that is generally violated in snow-dominated environments. Our new estimates confirm that high-elevation Alpine catchments have low Fyw values, spanning from 8 to 11%. Such low values have previously been interpreted as the impact of seasonal snow storage alone, but our comparison of different Fyw estimation methods suggests that these low Fyw values result from a combination of both snow cover effects and longer storage in the subsurface. In contrast, in the highest elevation, glacier dominated catchment, Fyw is 3–4 times greater compared to the other two catchments, due to the lower storage and faster drainage processes. A future challenge, capturing spatio-temporal snowmelt isotope signals during winter baseflow and the snowmelt period, remains to improve constraints on the Fyw estimation technique.

DATA AVAILABILITY STATEMENT

All data and accompanying Matlab files to support the analyses and findings presented in this work is included in Data S2.

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