the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 28 Nov 2024
Catchment hydrological response and transport are affected differently by precipitation intensity and antecedent wetness
Abstract. Hydrological response and transport are distinct catchment behaviours that have both been intensively studied, but rarely together. The hydrologic response characterises how quickly, and how strongly, streamflow reacts to precipitation inputs, whereas transport characterises how quickly precipitation reaches the stream. Here we use sub-daily time series of hydrometeorological fluxes and stable water isotopes to quantify both hydrological response and transport in two intensively studied temperate catchments. Consistent with previous studies, we find that hydrologic response is much quicker than transport. However, we also find that catchment wetness and precipitation intensity influence hydrologic response and transport in different ways. Increased antecedent wetness results in stronger runoff responses, primarily mobilising more old water, while increased precipitation intensity results in a faster propagation of the runoff response signal, and the delivery of greater proportions of recent precipitation to streamflow. Considered together, response times and travel times provide insights into runoff generation mechanisms, flow paths, and water sources.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Hydrology and Earth System Sciences.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.- Preprint
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Status: final response (author comments only)
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RC1: 'Comment on hess-2024-371', Markus Hrachowitz, 29 Nov 2024
The comment was uploaded in the form of a supplement: https://hess.copernicus.org/preprints/hess-2024-371/hess-2024-371-RC1-supplement.pdf
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AC1: 'Reply on RC1', Julia Knapp, 20 Dec 2024
The comment was uploaded in the form of a supplement: https://hess.copernicus.org/preprints/hess-2024-371/hess-2024-371-AC1-supplement.pdf
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AC1: 'Reply on RC1', Julia Knapp, 20 Dec 2024
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RC2: 'Comment on hess-2024-371', Anonymous Referee #2, 10 Feb 2025
The study by Knapp et al. investigates how precipitation intensity and antecedent wetness differently affect catchment hydrological response and transport. Using sub-daily hydrometeorological data and stable water isotopes in two catchments in Europe, the authors give evidence that hydrological response (streamflow reaction to rainfall) is much faster than transport (movement of precipitation to the stream). They find that increased antecedent wetness strengthens runoff responses by mobilizing older water, whereas higher precipitation intensity accelerates runoff signals and delivers more recent precipitation to streamflow. These findings provide insights into runoff generation, flow paths, and water sources.
The paper is written well and concise. The applied methodology and its findings are novel in will certainly contribute in advance catchment research. Some suggestions for minor revision in the following.
Introduction:
I think the "old water paradox " needs to be presented in a bit more detail. It is indeed not as detailed as what this study is about to present but it is worth mentioning that it has been known for a very long time that hydrodynamic responses have been found to be much faster than hydrogeochemical responses (by different tracers, often using end-member mixing analysis or similar)
As I remember the discussion of some of these studies, there were more possible explanations for this behavior. Wetness, but also something called transmissivity feedback, and the possibility, that unsaturated (but almost saturated) zones become saturated and all the "old water" that was previously immobile, becomes mobile again, e.g. in the riparian zone. Maybe these explanations could also be mentioned and possibly discussed.
Site descriptions and datasets
These two subsections are relatively short, which makes sense. But since differences of the two sites will be discussed later, it would be helpful seeing a direct comparison of their main characteristics in a table
Data analysis
Wetness quantification: it seems that wetness is considered to be related to the mobile storage, which is considered to be in relations with discharge. This would disregard wetness in the soils or the unsaturated zone, right? If so, please clarify. I think this might also be a possible reason why changes in antecedent wetness do not have an apparent effect on shallow flow paths. It might, if you quantify it differently (e.f. subsurface storm flow doesn't require saturated conditions, so the wetness metric of this study wouldn’t be a good proxy for it)
Figure 1: if space allows it, it would be good seeing both subfigures beside each other (discharge/P and isotopes of both catchments besides each other)
Subsection 2.3.3: in addition to the equation some explanation should be give on why backward and forward new water fractions are calculated and how they can be interpreted. This is well done in 3.4 but could be mentioned already up here.
Results and discussion
I think it would be worth clarifying what the term "infiltration" is meaning in this study as it seems that it is used to describe infiltration into the groundwater storage/aquifer, which is often referred to by "recharge". I assume that the authors had good reasons to speak about infiltration rather than recharge (or storage, rather than aquifer) but it would be good mentioning this early in the manuscript.
I very much like figure 6! But it also made me think how much it adds to the knowledge compared to the pre-event water / event water studies that have been published in the past. The methodology and datasets of this study are new and unique. In the results section the authors reveal very differentiated insights over hydrodynamics and transport dynamics over a large number of events. I think, if this differentiated information could be somehow added to this figure or be added to the general take-home message of the paper, it would be even more appealing to read it.
Finally, in a volume not too excessive, it would also be great to discuss the spatial domain to which the perceptual model in figure 6 could be applied when thinking beyond hillslope scales, and to which types of aquifer it may be most applicable to. Especially in flat terrains and for larger catchments, only regions closer to the stream show such obvious behaviour. I am wondering about it as it brings up the question how well groundwater models and surface models should be coupled and whether lumped or distributed schemes ar most adequate to accommodate the observed processes.
Citation: https://doi.org/10.5194/hess-2024-371-RC2 -
AC2: 'Reply on RC2', Julia Knapp, 05 Mar 2025
The comment was uploaded in the form of a supplement: https://hess.copernicus.org/preprints/hess-2024-371/hess-2024-371-AC2-supplement.pdf
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AC2: 'Reply on RC2', Julia Knapp, 05 Mar 2025
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