Associate editor
1. I wonder about the significance of (subsurface) lateral flow in your CZO? In your Eqs. 1-2, you
included streamflow. I assume that referred to actual stream discharge measured? With 7-18o slope,
many shallow soils, and hard soil-bedrock interface in upper reaches of the basin, I'm curious about
whether subsurface lateral flow down the hillslope would be an unavoidable factor influencing the water
budget at (some) locations of soil moisture sensors? Related to this issue, on p. 2 line 23, you indicated
that "we speculate that the deep drainage is stored locally in the deeper regolith .," here I also wonder
about the likelihood/degree of possible lateral flow down the slope (especially during snowmelt period)?
Some clarification along this line would be helpful to the overall understanding of your results presented.
Response: Yes, lateral flow undoubtedly contributed to the lower spatial variability in VWC
than in snow depth. Acknowledgement of lateral flow added.
2. It is good that you compared south- vs. north-facing slope soil moisture. Since there was no significant
difference in texture between south- vs. north-facing slopes (p. 9 line 237 and Fig. 2), I wonder whether
soil thickness might be different between south- vs. north-facing slopes that might contribute to the
observed soil moisture difference between south- vs. north-facing slopes (e.g., Fig. 8d)?
Response: With the 30-m DEM, there was no apparent difference in soil depth with aspect.
3. Can you clarify a bit on the locations of the 27 nodes and 11 trees vs. 3 soil types listed in Table 1?
Perhaps you could add some nodes' location information in Table 1? Alternatively, you might consider
adding a soil map to Fig. 1 a) as a background information? Also, I'm a bit confused with the number of
27 nodes. Since there were 11 trees and 3 sensor arrays per location (canopy, drip edge, and open),
shouldn't the total number of nodes be 33? Am I missing something here?
Response: Number and distribution of nodes clarified in text. Only one open per location,
not per tree. Map of soil families added to Figure 3.
4. I wonder how you reached and installed soil moisture sensors at 90 m depth in the 30-cm diameter
hole? (p. 6 line 120-)
Response: Long arms; a 30-cm diameter hole is large enough.
5. P. 7 lines 152-153: could you spell out the formula used in this conversion from VWC to total soil
water storage, given the different soil horizon depths shown in Table 1 and the varying soil thickness
shown in Fig. 3?
Response: Clarified in text.
6. Table 2 column for ΔSs: I assume 0 here is due to the truncation of decimals? May be better to use
decimals.
Response: The aim for this column is to show that over a year, change in storage did not
contribute to the overall water balance. Additional digits not needed.
7. Fig. 1: what is the background map in b) and c)? Would it be more informative to use soil depth map
as the background map instead? This may also help partially answer my comment #2 above.
Response: Background map is a digital photo. Soils information added to Figure 3.
8. Fig. 11: It would be better to spell out OND etc. in the caption.
Response: Done.
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Reviewer 1
Ln 20 and 21. I didn't see the evidence for short circuiting in some locations in the paper
Response: Agreed, statement revised.
Line 8 "and" after )
Done
Intro. Throughout refer to precipitation measured with rain gauges. At least for the study site, it would
be useful to know what those gauges are-they are clearly being used to measure both liquid and solid
precipitation
Response: Information added.
Ln 40 "," after elevations
Done
Might note that there have been at least a couple of relevant studies conducted in somewhat similar
conditions to those in this study---Williams et al., 2009, HESS 13:1325-1336 and Grant et al., 2004, HP
18: 3493-3511
Response: Reference added.
Ln 107 comma after stations
Done
Ln 125 comma after total and l after soi
Done
You probably don't want to get into these details, but the idea of using the Topp equation to "correct" soil
moisture data really doesn't make sense. I understand that the ECHO measures the soil dielectric
(described in Kizito). Topp is generally used to relate dielectric to water content. I read your paper to
mean that the dielectric readings in oven dry soil were very low. You then added an offset to make oven
dry be zero and assumed that the remainder of the calibration is parallel to the Topp equation. I'm not
sure what others would read or that I am close to correct. In the end it's not clear how accurate the lab
calibration was.
Response: Changed the text to indicate that the use of the Topp Eq. was not a correction, but
just an attempt to standardize different relationships between the dielectric measurement and
soil water content. This was largely done to resolve measurement differences between two
different Decagon sensors, the 5TE and the ECHO-TM which are both used in the watershed
but process the raw values differently. The application of the Topp Eq. to the ECHO-TM
data had the added benefit of removing the negative VWC values at very dry conditions.
Decagon has since introduced a digital version of the TM sensor, the 5-TM ,which processes
raw data in the same way as the 5-TE and will eliminate this step.
Ln 154, excavation, representative
Done
What was the size of the undisturbed samples?
Response: Text modified to indicate that undisturbed samples varied from 68 to 331cm3
Ln 160 laboratory,
Done
Water balance. I think you should make it clear that ΔS from two locations, one in P303 and one at the
lower met site, is assumed to apply to streamflow at P301 and P303.
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Response: Point added in discussion section.
Ln 200+ I don't see how you get SWE from the Judd sensors nor does it make sense that the timing to
Judd data would be systematically different from that in the "rain" gauge. If you use the snow depth data,
how good (uniform)-need some kind of indication for the water balance analysis.
Response: Average density from snow pillow multiplied by depth from Judd sensors to get
SWE; pls see text. Small differences in timing for recording of precipitation versus snow
depth changes do not affect the analysis, which is based on trends and cumulative quantities.
Ln 228 I wouldn't say that there was little variation in Ks-varied 21x
Response: This variability is still small over the possible range of Ks variability. Text
modified.
Ln 229 Seems like a contradiction-the statement that there is no consistent variation with depth is
followed by a discussion of how Ks varies with depth.
Response: We agree, and statement was changed accordingly.
Ln 231 Is there any reason (i.e., data) to attribute Ks to gravel and roots?
Response: Visual observations; now noted in text.
Ln 237 I'm accustomed to using the word "significant" in a statistical sense in scientific papers. I get the
idea you intend a more common vernacular meaning, is that so? If not, add an alpha value after the
word.
Response: changed to “apparent”.
Ln 293+ seems more like speculation than results. I think it should be deleted. Terms like linear, convex
or concave are not in the depth model and I don't know what those "results" are based on. Similarly, I
don't know what soil depth data you collected that indicate that the depth in one watershed is different
from another. Although I entirely agree that depth to bedrock may be important, that is hardly a result to
be presented here.
Response: Text modified to indicate that these are qualitative observations.
Ln 308 Something is wrong here. I think there were 2 main events in 08 and one in 09, but whatever, the
English is wrong as written.
Text corrected.
Ln 331 Looks to me like there is very little snow anywhere at either site by May 1.
Text corrected.
Ln 333 I haven't found a description of the methods for this.
Caption to Figure 6 clarified to explain density calculation.
Ln 338 as a comment--In my experience these water contents are extremely uniform
Text corrected.
Ln 361+ this is all reasonable-are there data to go with it -e.g., the undisturbed samples
Response: Parenthetical reference to coarse and very coarse sand fractions in Figure 2
added.
Ln 435-445 Talking of spatial variation, but the data don't look that variable. At any rate, this discussion
seems to be independent of the data presented. For example, I don't really see any evidence for local
runoff and runon. In fact, all the data support vertical infiltration as far as I can see. Nor do I see, for
example, how tree root uptake creates variability. I would expect the opposite, and that's the way the data
look to me.
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Response: Text clarified, meter scale.
Ln 454 I don't understand fig 10, but from fig 9 it seems that soil moisture doesn't change much until all
the snow is gone. This is also intuitive and observed elsewhere.
Response: Comparison made to April 5 vs. 27. Caption on Figure 10 clarified.
Water balance section. It is noted that there is a rapid streamflow response to water inputs. Perhaps I'm
sensitized to this, but I think it should be noted that it is extremely sensitive when the soil water storage is
greater than a threshold value of about 26 cm. Note the substantial rain and snowmelt the first 4 months
of 2009 with no effect on streamflow. This is described in depth by Seyfried et al., 2009 HP 23:858-873.
doi: 10.1002/hyp.7211.
Response: We agree. Point added to text.
Ln 492 No mention is made of underflow. That is, flow below the flume. Clearly there is a lot of water
moving into and through the "rock" -as you point out, that's what the trees use during summer. I know
that it's very difficult to quantify, and it may be quite small, but I think it should at least be mentioned.
Overall, I think the differences described should be presented in the context of the uncertainty of the
snowmelt input, which I expect is much greater than the differences discussed
Response: Text acknowledging this added.
I was struck by the large difference in runoff ratio between the two years but there seems to be no
discussion. Why is that?
Response: Quantities are actually very similar. Note also that 2008 data are not for the full
WY.
Ln 506+ The comparison of snow storage to soil storage is a bit misleading for two reasons. First, from a
water balance of view, you have to subtract 9 or 10 cm that is PWP or plant extraction limit, so the soil
storage is more like 15 cm, and secondly because, in this environment, the water inputs are much greater
than the snow pack storage at any given time.
Response: Good point. Text modified.
I'm not sure that fig 11 adds much and don't think that 11 b and c add even less.
Response: Figure simplified by reducing to a single panel that conveys the main point.
Conclusions. Texture difference leads to "significant" -is this based on the comparison of two sites?
Response: Yes, see Figure 8.
Conclusions 550. I think the intent is to distinguish between stochastic and deterministic variability. I
think that has important implications for modeling these systems.
Response: Point added.
Conclusions 553. I think you should consider the threshold idea mentioned previously as how streamflow
responds to soil moisture storage.
Response: Done.
Conclusions. I'm not sure how to reconcile the observation that the timing of soil moisture dry down
depends on snow melt dynamics with the earlier statement that, unlike snow, soil moisture responds only
to elevation.
Response: One is temporal and the other spatial. Text clarified.
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Reviewer 2
1. drip-edge, open, under canopy. The snow and soil moisture measurements are stratified by position
relative to individual trees (under canopy, drip edge, and open), and many of the figures include data
separated by position. I could not find any information about how close these measurements are from
each other, or how big the trees are around which the measurements are made. How far beyond the
canopy edge are the open samples? In the text, it states the trees are large (up to 50 m). Are the “open”
sensors only several meters from the drip edge of a 50 m tree, or are they in the middle of a clearing that
is 10’s of meters across? What considerations were made with regard to scaling between horizontal
distance from canopy edge and tree height? Were the trees around which observations were made of
‘average’ size within the stands (or big or small)?
“VWC did not show any distinct pattern with location relative to tree canopy (Figure 8b), indicating little or no
canopy effects on water infiltration or soil evaporation, and a uniform lateral distribution of root-water uptake,
irrespective of position within the local landscape.”
With no information on the horizontal spacing between sensor locations and size of trees selected, it is
hard to evaluate this statement.
Response: Under-canopy and drip-edge sensors were generally 2-3 m apart, with open
sensors generally 5-10 m away in clearings at least one tree height in extent. All 11 trees
were mature, 30-50 m tall, about 0.5 m in diameter at breast height, and with canopies
extending 2-4 m from the trunk. Text expanded.
2. Upward flow in soil?: As the manuscript is written, the authors (implicitly) preclude significant
upward flow in the soil during the summer months (from below 1 m towards the surface). For example,
they write:
“Late-summer VWC at all depths and locations approached low values of about 0.1 cm3 cm-3, indicating that both
streamflow and root-water uptake depend on deeper soil storage. Soil- moisture profiles showed higher nearsurface than deeper soil moisture in the winter, with an inversion occurring in spring and summer to lower VWC at
the near surface than at depth”.
“Because baseflow and ET continue after soils reach a plateau of dryness, further water is apparently drawn from
soil, saprolite and saprock at depths greater than 1 m.”
Were calculations made that show an upward flux is negligible? Or did they just assume that this is the
case because the soil is relatively coarse? Some portion of ET in summer may be sustained by a flux from
deeper-to-shallower soil horizons. I am not saying that this is the case, but it seems strange not to (a)
mention the possibility; and (b) do some simple calculations to show whether or not it is reasonable.
Response: No calculations made. This upward flux would not affect the interpretation of the
water budget in this paper, as the two ET terms end up combined in the Loss term. Whether
the ET comes from deeper water transported upward to shallower roots due to a moisture
gradient in the soil or deeper water taken up by deeper roots, the water comes from the
deeper compartment. Text regarding the two soil compartments added after Eq. [1].
3. Interception: The treatment of interception loss (sublimation and evaporation from the canopy) is
subpar, especially compared to the rest of the manuscript.
Response: The authors acknowledge the uncertainty in both precipitation and canopy
interception in this analysis. Text added near end of discussion section. To clarify analysis,
interception was included in equation 2; figures adjusted accordingly.
3.1 Amount of snow lost from the canopy to sublimation is assumed to be negligible based on the work
of Molotch et al.
“There could be an additional small correction for sublimation. Work by Molotch et al. (2007) reported values of
0.4‐0.7 mm d‐1 for sites in the Rocky Mountains. However, it should be small in these forested catchments, which
have low wind velocities.”
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This is not an accurate use of the data in the Molotch study for several reasons. First, Molotch’s sites are
much colder than the sites covered in the paper here (I would guess a temperature difference of ~10 deg
C if not more). Second, Molotch only studied mid-winter sublimation (day of year 60-100), not an entire
winter. Third, the 0.4 mm d-1 rate in Molotch is for sub-canopy sublimation, i.e. from the snowpack. The
0.7 mm d-1 rate is for canopy sublimation. (i.e., the 0.4 mm d-1 rate should not be mentioned in this
context). I have no idea how large the canopy sublimation loss is at the CA site discussed in the paper.
However, I am rather certain the 0.7 mm d-1 rate in Molotch et al. should be considered a minimum
estimate, and probably provides little constraint for the study here. There must be some other papers in
the literature that include more relevant information.
Response: Text and reference deleted.
3.2 Interception loss (summer and winter) seems to be treated as an afterthought, rather than an integral
part of the water budget. Interception should be included in equations 1 and 2. As written, interception is
not mentioned in the water balance, but is dealt with only towards the end of the paper (in the discussion
I think). This seems strange for a term that the authors suggest is ~20% of the input (line 454)
Response: Interception added to equations and more-explicitly considered.
3.3 Finally, some clarification about the position and number of rain gauges and the snow pillow relative
to canopies would be helpful (perhaps in a sub-section dedicated to interception). Are there only two rain
gauges (the manuscript says details are in another paper in review)? Are all the rain gauges are under
the tree canopies (I think) – from this the authors suggest that interception is therefore already accounted
for. At the same time, they mention in the text that stemflow could be important (line 442), so the subcanopy position of raingauges might underestimate water inputs. Is the snow pillow (used for density
calculations) under a canopy or in the open (the latter I presume). How does this impact the calculations
of inputs through the canopy.
Response: There are two rain gauges, located in clearings at least one tree height across; text
clarified. See also expanded treatment of rain interception, which is not acconted for in the
rain. Lack of spatially distributed precipitation measurements is still a limitation at the site.
This would also help with estimation of canopy interception.
4. Number of rain gauges and uncertainty: It is my understanding that only two rain gauges were used in
the study. This introduces significant uncertainty in the hydrologic budget (roughly half of the
precipitation is rainfall). Two significant sources of uncertainty should be addressed in the manuscript.
First, horizontal heterogeneity in rainfall is substantial in mountainous environments, at the scale of the
basin studied. Second, throughfall is heterogeneous at the scale of trees. Numerous papers exist on both
of these topics. If the authors are not going to assess this issue themselves, they should at least estimate
the uncertainty in their inputs based on previous studies.
Response: Text modified to note that the two rain gauges also matched two others at higher
elevation. Uncertainty in local-scale heterogeneity also acknowledged.
1. Abstract: Compared to the rest of the paper, the abstract is not well written. In particular, after
reading the abstract I had no what the purpose of the study was.
Response: Abstract revised to highlight the main aims & findings.
2. line 66: awkwardly written
Response: Sentence improved.
3. line 153: perhaps another sentence providing details would help. Were calculations based on the
midpoint between probes?
Response: Sentence augmented.
4. line 199: awkward.
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Response: Split into 2 sentences.
5. 225: are organic matter/bulk density values outside of the calibration tests of Kizito et al.?
Response: Kizito used several soils that encompass the bulk density values of the soils in the
field. Soil moisture measurements we made in the mineral soil beneath the organic rich
surface soils.
6. 371: how do you know the decrease is not from ET? Stating the rate (mm d-1) would be helpful.
Response: ET added to sentence, as we have other evidence that ET was occurring then.
7. 482: “assuming the declines are ET” is confusing as written
Response: Rewritten for clarity.
8. Figure 9 caption: It took me a while to rectify the text and the figure -- because I assumed (incorrectly)
that I could compare the magnitude of the precip and discharge lines in the figure. Only after careful
study, did I notice the different y-axis. Given the line down the middle of the figure (i.e., the side-by-side
panels), the y-axes as placed are confusing.
Response: Axis callouts added to caption.
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