|The authors have made a substantial effort by including extra simulations and experimental data in their revised paper, which is highly appreciated. |
Nevertheless, I think there are still a few issues that should be addressed.
First, the authors compared evaporation from layered (or top soil compacted) soils under saline and non-saline conditions with those from other soils and use these comparisons to draw conclusions on the effect of layering (or compaction) and salinity on evaporation. However, there are two issues the authors should pay attention to. First, they should always make clear with what they are referring, i.e. they have to clarify clearly the reference case. Second, they should define the reference case so that it is representative for the non-compacted soil. I do not agree that the case they are considering now as the reference case, namely the homogenized soil which has a much wider grain size distribution, than the layered soil that is used to represent a compacted soil, can be considered as a proxy for the non-compacted soil. Therefore, although the comparisons for the two cases: layered soils with layers of uniform grain sizes versus homogenized soil with mixed grain sizes is very interesting and illustrative, it does not represent a comparison between a compacted versus a non-compacted soil. Thus, it is not correct, to my opinion, to draw conclusions about the difference of evaporation between compacted and non-compacted soils based on this comparison. The comparison between the layered FU and CU soils is already interesting on its own and I am wondering what the additional value of the homogeneous HO scenario in fact is. To my opinion, it represents the behavior of another porous medium with a much wider pore size distribution. One could consider leaving it out and replacing it by a numerical simulation but using a homogenous soil profile that corresponds with the properties of the lowest layer (although this might be a bit extreme in hydraulic property contrast between the top and bottom).
Second, improve the quality of figure 7.
Third, explain in figure 11 why stage 1 evaporation of the saline compacted sand soil column is much smaller than the stage 1 evaporation of the saline non-compacted sand column.
Ln 119: ‘It was shown that porous media composed of a fine texture domain that overlies a coarse texture domain may result in longer duration of S1 and increased cumulative evaporation.’ As I commented in my previous review, it is important to mention the reference case. With respect to what does this layered medium evaporates more? With respect to a homogeneous coarse domain or a homogeneous fine domain? I think it is in most cases correct to state that the layered profile (with fine on top) will have more S1 evaporation than the uniform coarse profile. The depth of the drying front (i.e. where the transition between saturated and unsaturated conditions take place) in the coarse layer will be translated downward by approximately the thickness of the fine layer (if the thickness of the fine layer is smaller than its characteristic length) so that the same amount can be extracted from the coarse layer during S1 evaporation in the layered system as in the homogeneous coarse soil. Since water is also extracted from the fine layer on top, the total amount of water that can be evaporated from the layered system will be larger than the amount of water that is extracted from the coarse layer. Whether the layered system with a fine layer on top will evaporate more during S1 than a uniform fine layer, depends on the characteristic lengths of the fine and coarse soils, the thickness of the fine layer, and on the initial water content (or porosity when evaporation of a saturated soil is considered). When the thickness of the fine layer is much smaller than its characteristic length and when the stage 1 evaporation from the uniform coarse soil is lower than that from the uniform fine soil, the layered soil will evaporate less during stage 1 than the uniform fine soil. When the thickness of the fine layer is larger than its characteristic length, the layered soil will evaporate the same amount of water than the uniform fine soil. When the thickness of the fine layer is close to its characteristic length but smaller, then extra water can be wicked from the coarse layer below the fine layer at relatively low capillary pressures. Of course, this extra wicking is only possible when the water reservoir in the coarser layer did not drain by gravity (e.g. when there is a shallow water table).
Ln 125 ‘Consequently, the coarse texture layer acts as a water reservoir that supplIES extra water to sustain a longer S1 and higher cumulative evaporation, compareD to a homogeneous FINE? soil structure.’ See comment above. Can’t it be stated that the thickness of the fine layer should be larger than Lcfine*delta_theta_fine – Lccoarse*delta_theta_coarse? In the line below, you mention that the fine layer should not be thicker than a certain threshold, which I understand. But, I think it should also not be thinner than another threshold.
Ln 152: ‘In some cases, if the precipitated salt layer over the soil surface is hydraulically connected to the solution in the pores below, it may accelerate evaporation, as the surface area of the precipitated salt is usually higher compared to the underlying bare soil. Consequently, as long as the salt crust can pump liquid water from the underlying media, the elevated surface area of the salt crust would increase total evaporation’ Why would an increase in surface area increase the evaporation? I think this would be related to the increase in surface roughness which increases for the same wind speed the latent and sensible heat exchange. This would imply an increased S1 evaporation.
Ln 218: compareD to…
Ln 225: The salt crust will reduce (skip s)
Ln 338, layer 60-80 mm: why does this layer have such a low porosity. Also the mixed layer has a much lower porosity than most of the layers in the layered soil profile.
Ln 523: compareD to
Ln 550: I am still not convinced that a comparison between a simulation of a layered porous medium consisting of layers with a different textures and a porous medium that represents a mixture of the grain sizes of these layers is appropriate for a comparison between compacted versus non-compacted soils. This homogeneous layer would not represent a non-compacted soil. I think the layered medium should be compared with a homogeneous profile that either consists of the layer with the coarsest texture or the layer with the finest texture.
Ln568 Figure 7. The figure is hardly readable since the legend of the figure does not explain all the lines shown in the figure.
Ln571: I do not understand which simulation results are shown here. When the evaporation is still in s1, the evaporation flux at the top of the soil and the interface with the salt crust should be nearly equal to the potential evaporation rate. But it is much smaller in the simulation. How can these simulation results then still represent S1 evaporation?
Ln 666: ‘no salt crust was observed (in CU) because of the low cumulative evaporation’ I don’t think that the low cumulative evaporation can explain this since the cumulative evaporation was nearly as high in CU as HO. In HO, a salt crust was built up. I think the reason is mainly the fact that in HO, the evaporation front remains longer at the soil surface so that all salt accumulation occurs there.
Ln 747: ‘The differences in the impact of salinity on evaporation between the HO and FU setups (Figures 9-10), together with the differences in patterns of drying (Figure 8), support the research hypothesis that even though more salt accumulation on the surface is expected in compacted conditions, its impact on evaporation is expected to be moderate compared to neutral conditions, since the hydraulic connection to the surface persists longer and includes the salt crust.’ The problem is that the HO setup must not be considered as the ‘neutral condition’. The HO is a different porous medium than the FU and does not represent the ‘uncompacted analogue’ of FU. The closest that comes to the uncompacted analogue is the CU setup.
Ln 775: ‘an experiments’ Skip ‘an’.
Ln 785: ‘For saline conditions the compacted sand also displayed higher cumulative evaporation compared to the uncompacted state, with total cumulative evaporation of about 16.5 mm and 14.5 mm, for the compacted and uncompacted samples, respectively (Figure 11).’ Under saline conditions, the cumulative evaporation is indeed larger for the compacted sand than for the uncompacted sand.But why is the stage 1 evaporation in the compacted sand much lower than in the uncompacted sand?