In:
Hydrology and Earth System Sciences, Copernicus GmbH, Vol. 22, No. 7 ( 2018-07-19), p. 3841-3861
Abstract:
Abstract. The young water fraction Fyw, defined as the proportion of
catchment outflow younger than approximately 2–3 months, can be estimated
directly from the amplitudes of seasonal cycles of stable water isotopes in
precipitation and streamflow. Thus, Fyw may be a useful metric in
catchment inter-comparison studies that investigate landscape and
hydro-climatic controls on streamflow generation. Here, we explore how
Fyw varies with catchment characteristics and climatic forcing,
using an extensive isotope data set from 22 small- to medium-sized
(0.7–351 km2) Swiss catchments. We find that flow-weighting the tracer
concentrations in streamwater resulted in roughly 26 % larger young water
fractions compared to the corresponding unweighted values, reflecting the
fact that young water fractions tend to be larger when catchments are wet and
discharge is correspondingly higher. However, flow-weighted and unweighted
young water fractions are strongly correlated with each other among the
catchments. They also correlate with terrain, soil, and land-use indices, as
well as with mean precipitation and measures of hydrologic response. Within
individual catchments, young water fractions increase with discharge,
indicating an increase in the proportional contribution of faster flow paths
at higher flows. We present a new method to quantify the discharge
sensitivity of Fyw, which we estimate as the linear slope of the
relationship between the young water fraction and flow. Among the
22 catchments, discharge sensitivities of Fyw are highly variable
and only weakly correlated with Fyw itself, implying that these
two measures reflect catchment behaviour differently. Based on strong
correlations between the discharge sensitivity of Fyw and several
catchment characteristics, we suggest that low discharge sensitivities imply
greater persistence in the proportions of fast and slow runoff flow paths as
catchment wetness changes. In contrast, high discharge sensitivities
imply the activation of different dominant flow paths during precipitation
events, such as when subsurface water tables rise into more permeable layers
and/or the river network expands further into the landscape.
Type of Medium:
Online Resource
ISSN:
1607-7938
DOI:
10.5194/hess-22-3841-2018
DOI:
10.5194/hess-22-3841-2018-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2018
detail.hit.zdb_id:
2100610-6
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