Investigating young water fractions in a small Mediterranean mountain catchment: both precipitation forcing and sampling frequency matter
The young water fraction (Fyw), the proportion of water younger than 2-3 months, was investigated in soil-, ground- and stream waters in the 0.56 Km2 sub-humid Mediterranean Can Vila catchment. Rain water was sampled at 5-mm rainfall intervals. Mobile soil water and groundwater were sampled fortnightly, using suction lysimeters and two shallow wells, respectively. Stream water was dynamically sampled at variable time intervals (30 minutes to 1 week), depending on flow. A total of 1,529 18O determinations obtained during 58 months were used. The usual hypothesis of rapid evapotranspiration of summer rainfall could not be maintained, leading to discard the use of an “effective precipitation” model. Soil mobile waters had Fyw up to 34%, while in ground and stream were strongly related to water table and discharge variations, respectively. In stream waters, due to the highly skewed flow duration curve, the flow-averaged young water fraction (F*yw) was 22.6%, whereas the time-averaged Fyw was 6.2%. Nevertheless, both F*yw and its exponential discharge sensitivity (Sd) showed relevant changes when different 12-month sampling periods were investigated. The availability of Sd and a detailed flow record allowed us to simulate the young water fraction that would be obtained with a virtual thorough sampling (F**yw). This showed that underestimation of F*yw is associated with missing the sampling of highest discharges and revealed underestimations of F*yw by 25% for the dynamic sampling and 66% for the weekly sampling. These results confirm that the young water fraction and its discharge sensitivity are metrics that depend more on precipitation forcing than on physiographic characteristics, so the comparisons between catchments should be based on mean annual values and inter-annual variability. They also support the dependence of the young water fraction on the sampling rate and show the advantages of flow-weighted F*yw. Water age investigations should be accompanied by the analysis of flow duration curves. In addition, the simulation of F**yw is proposed as a method for checking the adequacy of the sampling rate used.
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2020-05
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Online Access: | http://hdl.handle.net/10261/211200 |
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dig-idaea-es-10261-2112002020-05-13T01:08:34Z Investigating young water fractions in a small Mediterranean mountain catchment: both precipitation forcing and sampling frequency matter Gallart, Francesc Valiente, María Llorens, Pilar Cayuela, Carles Latron, Jérôme Gallart, Francesc [0000-0002-7050-2204] Llorens, Pilar [0000-0003-4591-5303] Latron, J. [0000-0003-3253-6734] Young water fraction Precipitation The young water fraction (Fyw), the proportion of water younger than 2-3 months, was investigated in soil-, ground- and stream waters in the 0.56 Km2 sub-humid Mediterranean Can Vila catchment. Rain water was sampled at 5-mm rainfall intervals. Mobile soil water and groundwater were sampled fortnightly, using suction lysimeters and two shallow wells, respectively. Stream water was dynamically sampled at variable time intervals (30 minutes to 1 week), depending on flow. A total of 1,529 18O determinations obtained during 58 months were used. The usual hypothesis of rapid evapotranspiration of summer rainfall could not be maintained, leading to discard the use of an “effective precipitation” model. Soil mobile waters had Fyw up to 34%, while in ground and stream were strongly related to water table and discharge variations, respectively. In stream waters, due to the highly skewed flow duration curve, the flow-averaged young water fraction (F*yw) was 22.6%, whereas the time-averaged Fyw was 6.2%. Nevertheless, both F*yw and its exponential discharge sensitivity (Sd) showed relevant changes when different 12-month sampling periods were investigated. The availability of Sd and a detailed flow record allowed us to simulate the young water fraction that would be obtained with a virtual thorough sampling (F**yw). This showed that underestimation of F*yw is associated with missing the sampling of highest discharges and revealed underestimations of F*yw by 25% for the dynamic sampling and 66% for the weekly sampling. These results confirm that the young water fraction and its discharge sensitivity are metrics that depend more on precipitation forcing than on physiographic characteristics, so the comparisons between catchments should be based on mean annual values and inter-annual variability. They also support the dependence of the young water fraction on the sampling rate and show the advantages of flow-weighted F*yw. Water age investigations should be accompanied by the analysis of flow duration curves. In addition, the simulation of F**yw is proposed as a method for checking the adequacy of the sampling rate used. This research was supported by the projects TransHyMed (CGL2016‐75957‐ R AEI/FEDER, UE) and MASCC‐ DYNAMITE (PCIN‐2017‐061/AEI) funded by the Spanish Ministerio de Ciencia, Innovación y Universidades, as well as the grant SGR 2017 1643 funded by the Generalitat de Catalunya. C. Cayuela was the beneficiary of a predoctoral FPI grant (BES‐2014‐070609) funded by the Spanish Ministry of Economy and Competitiveness and the contribution by M. Sprenger was supported by the Deutsche Forschungsgemeinschaft (project no. 397306994). We are grateful to G. Bertran, M. Roig-Planasdemunt and E. Sánchez for their support during field work at the Can Vila catchment, to J. Kirchner, J. von Freyberg and K. Beven for their comments, as well as to M. Eaude for his English style improvements. Peer reviewed 2020-05-12T16:14:55Z 2020-05-12T16:14:55Z 2020-05 artículo http://purl.org/coar/resource_type/c_6501 Hydrological Processes (2020) http://hdl.handle.net/10261/211200 10.22541/au.157979613.39458719 en Preprint 10.22541/au.157979613.39458719 Sí open Wiley-Blackwell |
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Young water fraction Precipitation Young water fraction Precipitation Gallart, Francesc Valiente, María Llorens, Pilar Cayuela, Carles Latron, Jérôme Investigating young water fractions in a small Mediterranean mountain catchment: both precipitation forcing and sampling frequency matter |
description |
The young water fraction (Fyw), the proportion of water younger than 2-3 months, was investigated in soil-, ground- and stream waters in the 0.56 Km2 sub-humid Mediterranean Can Vila catchment. Rain water was sampled at 5-mm rainfall intervals. Mobile soil water and groundwater were sampled fortnightly, using suction lysimeters and two shallow wells, respectively. Stream water was dynamically sampled at variable time intervals (30 minutes to 1 week), depending on flow. A total of 1,529 18O determinations obtained during 58 months were used. The usual hypothesis of rapid evapotranspiration of summer rainfall could not be maintained, leading to discard the use of an “effective precipitation” model. Soil mobile waters had Fyw up to 34%, while in ground and stream were strongly related to water table and discharge variations, respectively. In stream waters, due to the highly skewed flow duration curve, the flow-averaged young water fraction (F*yw) was 22.6%, whereas the time-averaged Fyw was 6.2%. Nevertheless, both F*yw and its exponential discharge sensitivity (Sd) showed relevant changes when different 12-month sampling periods were investigated. The availability of Sd and a detailed flow record allowed us to simulate the young water fraction that would be obtained with a virtual thorough sampling (F**yw). This showed that underestimation of F*yw is associated with missing the sampling of highest discharges and revealed underestimations of F*yw by 25% for the dynamic sampling and 66% for the weekly sampling. These results confirm that the young water fraction and its discharge sensitivity are metrics that depend more on precipitation forcing than on physiographic characteristics, so the comparisons between catchments should be based on mean annual values and inter-annual variability. They also support the dependence of the young water fraction on the sampling rate and show the advantages of flow-weighted F*yw. Water age investigations should be accompanied by the analysis of flow duration curves. In addition, the simulation of F**yw is proposed as a method for checking the adequacy of the sampling rate used. |
author2 |
Gallart, Francesc [0000-0002-7050-2204] |
author_facet |
Gallart, Francesc [0000-0002-7050-2204] Gallart, Francesc Valiente, María Llorens, Pilar Cayuela, Carles Latron, Jérôme |
format |
artículo |
topic_facet |
Young water fraction Precipitation |
author |
Gallart, Francesc Valiente, María Llorens, Pilar Cayuela, Carles Latron, Jérôme |
author_sort |
Gallart, Francesc |
title |
Investigating young water fractions in a small Mediterranean mountain catchment: both precipitation forcing and sampling frequency matter |
title_short |
Investigating young water fractions in a small Mediterranean mountain catchment: both precipitation forcing and sampling frequency matter |
title_full |
Investigating young water fractions in a small Mediterranean mountain catchment: both precipitation forcing and sampling frequency matter |
title_fullStr |
Investigating young water fractions in a small Mediterranean mountain catchment: both precipitation forcing and sampling frequency matter |
title_full_unstemmed |
Investigating young water fractions in a small Mediterranean mountain catchment: both precipitation forcing and sampling frequency matter |
title_sort |
investigating young water fractions in a small mediterranean mountain catchment: both precipitation forcing and sampling frequency matter |
publisher |
Wiley-Blackwell |
publishDate |
2020-05 |
url |
http://hdl.handle.net/10261/211200 |
work_keys_str_mv |
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_version_ |
1777669404773842944 |