the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 08 May 2026
Linking hydrological responses in forest ecosystems to atmospheric forcing
Abstract. Across ecosystems, soil water is replenished by precipitation events and depleted by evapotranspiration. Evapotranspiration is driven by solar radiation and the aerodynamic evaporative demand of the atmospheric boundary layer (Eaero). However, vegetation regulates the rate of transpiration through species-specific stomatal closure mechanisms that depend on tree water status, which in turn depends on the tree’s water supply and the atmospheric water demand. Therefore, quantifying the effects of precipitation, solar radiation and Eaero on tree-mediated water fluxes is challenging. Here we use ERRA, a framework for de-mixing and de-convolving non-stationary system responses to multiple inputs, to quantify how atmospheric forcing affects ecosystem water fluxes and water content dynamics in a mixed beech and spruce forest. The resulting impulse-response functions describe how soil and tree water fluxes respond to three atmospheric forcing (precipitation, solar radiation, Eaero). Water contents of soils and trees responded positively and rapidly to precipitation pulses, indicating fast infiltration of precipitation into the soil and net increases in tree water contents. Tree water contents responded more clearly to precipitation inputs than sapflow rates did, suggesting that precipitation primarily reduced transpiration rather than enhancing tree water uptake. Trees responded quickly and strongly to impulses of solar radiation, but their responses to Eaero were less distinct, potentially reflecting stomatal closure effects on transpiration. The impulse-response functions reflected species-specific water use strategies and differences in hydraulic capacitance of trees, which buffered root water uptake during periods of high transpiration demand and thus prolonged the refilling of tree water storage after precipitation events. Impulse responses to solar radiation and Eaero were much less distinct in the soils than in the trees, illustrating how forest canopies shield the underlying soils from atmospheric forcing. Our study highlights how impulse-response functions can help to identify soil-plant-atmosphere relations, complementing our understanding of forest ecosystem functioning in response to atmospheric forcing.
- Preprint
(3745 KB) - Metadata XML
- BibTeX
- EndNote
Status: open (until 17 Sep 2026)
-
RC1: 'Comment on egusphere-2026-2481', David Ellison, 19 Jun 2026
reply
-
AC1: 'Reply on RC1', Stefano Martinetti, 17 Aug 2026
reply
I found this a fascinating and exceptional assessment/discussion of the drivers and explanatory factors behind evapotranspiration in spruce and beech stands in Switzerland (greater Zurich area). Most of my "larger" comments are comparatively minor and amount to suggestions for potential tweaks/improvements to the text. In general, though, I would not want to change that much. But perhaps my comments will nonetheless prove useful for sharpening the final draft. For more detail, please see the attached, commented submission pdf.
Thank you for your assessment of the manuscript and for your helpful comments and pdf-annotations. These suggestions will be helpful in revising our manuscript, resolving minor issues and strengthening the manuscript. In the following we provide detailed response (in bold) to the reviewer’s questions (in italics).
I do, however, have two-three larger questions that may prove interesting either for this paper, or perhaps for future work.
First, in reading this, I found myself frequently reflecting on the concept of "residence times". The paper never really comes out directly to address this concept. But nonetheless, it seems very prominently interested in and curious about the residence times of water in different tree species, stem, branch, soil and perhaps landscape contexts. Of course, to some extent, these residence times are likely to be partly driven by variation in the intensity and/or magnitude of the precipitation pulse. But still, it seems interesting to think about these questions in this larger context of the various residence times, and how these are affected by climatic variations, tree species type, and the like... I also wonder a bit how such residence times might be graphically displayed...Thank you for this comment. We agree that the analysis of residence times would be interesting and a logical next step for follow up work. However, it is important to highlight that what we show in the manuscript are solely response times to different impulses (i.e., the wave celerity with which changes in inputs are translated into changes in outputs) and not the actual residence times (i.e., the time required for material to be transported through the system). It has been recognized for decades in hydrology that these are different time scales controlled by different mechanisms. For example, the residence time of precipitation in the soil-plant atmosphere continuum (SPAC) might be orders of magnitudes longer (days to months) compared to the response of soils and plants to a precipitation impulse (days). A detailed analysis of residence times would require tracer data across the SPAC at a similar resolution as the water fluxes. For example, recently, Knapp et al. (2025) quantified catchment hydrological response and travel time distributions in two catchments (Erlenbach and Upper Hafren catchments) under varying wetness conditions. However, contrary to the study of Knapp et al., we currently do not have high-resolution measurements of stable water isotopes (or any other tracer) required to quantify residence/travel times of water along the pathway through the SPAC. In the revised version of the manuscript, we will expand our discussion to make the distinction between response times and residence times clearer.
Second, I find myself wondering a lot about how the tree growth cycle is affected by the various water related fluxes described herein. Though the carbon flux is not assessed here in this particular paper, all the assessed variations in things like sap flow, tree water content, and the ET flux are presumably all tightly linked to variations in growth-related outcomes... Thus, it would be interesting to learn more about how these phenomena are linked.
Thank you for this comment. We agree that transpiration (and the available measurements of water fluxes and potentials along the SPAC) and carbon uptake, allocation and plant growth are somewhat related. Our dendrometer measurements might even allow us to estimate tree growth. However, tree growth occurs over much longer timescales than the time windows in which trees respond to climate forcing captured by impulse-response functions. Also, potential tree growth responses to varying atmospheric control variables are difficult to observe because they occur more continuously than, for example, the more abrupt closure of stomata (and the resulting reduction in sapflow). While there is a link between stomatal conductance and tree growth, it is still difficult to quantify it based on the observed dynamics and we’d argue that this can only be looked at the scale of entire months & growing seasons in longer time series. We will nonetheless try to address these aspects in the discussion more prominently.
Together, these points seem to suggest that the current draft of these paper leaves some open questions about the larger take-home messages being crafted here. One of the more important strengths of this paper is the willingness of the Authors to wallow in the most rudimentary of details. But I wonder if this draft, at least, is perhaps a bit lost in the details while missing the bigger picture. What are they really trying to say, perhaps, about possible tipping points and/or the survival limits of different tree species types relative to the changing climatic conditions they currently face?
I feel like there is a larger picture here that is not quite made transparent, but is looming in the background. The Authors seem to make a convincing case for the ERRA analysis framework they deploy. But what are the ultimate implications of this analysis? And what are the principal goals of this paper?
This is an interesting point, and we appreciate the reviewers statement. We agree that in the manuscript, we show a very detailed analysis of the measurements. This was partially made possible through ERRA, which allowed us to detect details in the dataset that otherwise would be much more difficult to quantify (for example, the differences in responses to Eaero and solar radiation). The current focus of the paper on process measurements might indeed give the impression that we might be missing the bigger picture. However, because our current analysis is based on data at only one location across only five years on a limited number of tree replicates per species, we want to avoid creating the impression that our results are a benchmark for other central European forested ecosystems. Therefore, quantifying and reporting on “tipping points and/or the survival limits of different tree species types relative to the changing climatic conditions” in a more general way would be highly speculative and would greatly oversell our results. Nonetheless, we will thoroughly discuss potential broader implications of our results in the revised version of the manuscript.All-in-all, I am not necessarily expecting the Authors to integrate these factors into the current paper. These comments are mentioned more as food for thought, all points provoked by what is generally a fascinating and very detailed discussion of tree water fluxes under varied conditions. Still, I hope there is something useful here.
We thank the reviewer again for his positive assessment and for providing an additional viewpoint on the presented findings in our manuscript.
Citation: https://doi.org/10.5194/egusphere-2026-2481-AC1
-
AC1: 'Reply on RC1', Stefano Martinetti, 17 Aug 2026
reply
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 184 | 80 | 17 | 281 | 24 | 25 |
- HTML: 184
- PDF: 80
- XML: 17
- Total: 281
- BibTeX: 24
- EndNote: 25
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
I found this a fascinating and exceptional assessment/discussion of the drivers and explanatory factors behind evapotranspiration in spruce and beech stands in Switzerland (greater Zurich area). Most of my "larger" comments are comparatively minor and amount to suggestions for potential tweaks/improvements to the text. In general, though, I would not want to change that much. But perhaps my comments will nonetheless prove useful for sharpening the final draft. For more detail, please see the attached, commented submission pdf.
I do, however, have two-three larger questions that may prove interesting either for this paper, or perhaps for future work.
First, in reading this, I found myself frequently reflecting on the concept of "residence times". The paper never really comes out directly to address this concept. But nonetheless, it seems very prominently interested in and curious about the residence times of water in different tree species, stem, branch, soil and perhaps landscape contexts. Of course, to some extent, these residence times are likely to be partly driven by variation in the intensity and/or magnitude of the precipitation pulse. But still, it seems interesting to think about these questions in this larger context of the various residence times, and how these are affected by climatic variations, tree species type, and the like... I also wonder a bit how such residence times might be graphically displayed...
Second, I find myself wondering a lot about how the tree growth cycle is affected by the various water related fluxes described herein. Though the carbon flux is not assessed here in this particular paper, all the assessed variations in things like sap flow, tree water content, and the ET flux are presumably all tightly linked to variations in growth-related outcomes... Thus, it would be interesting to learn more about how these phenomena are linked.
Together, these points seem to suggest that the current draft of these paper leaves some open questions about the larger take-home messages being crafted here. One of the more important strengths of this paper is the willingness of the Authors to wallow in the most rudimentary of details. But I wonder if this draft, at least, is perhaps a bit lost in the details while missing the bigger picture. What are they really trying to say, perhaps, about possible tipping points and/or the survival limits of different tree species types relative to the changing climatic conditions they currently face?
I feel like there is a larger picture here that is not quite made transparent, but is looming in the background. The Authors seem to make a convincing case for the ERRA analysis framework they deploy. But what are the ultimate implications of this analysis? And what are the principal goals of this paper?
All-in-all, I am not necessarily expecting the Authors to integrate these factors into the current paper. These comments are mentioned more as food for thought, all points provoked by what is generally a fascinating and very detailed discussion of tree water fluxes under varied conditions. Still, I hope there is something useful here.