Climate Change Impacts on Groundwater Recharge in Cold and Humid Climates: Controlling Processes and Thresholds

Round 1

Reviewer 1 Report

The authors addressed and tried to revise the manuscript “Climate change impacts on groundwater recharge in cold and humid climates: controlling processes and thresholds” as per the comments that I mentioned in the first-round review. Although the authors mentioned that Dubois et al. [22] is accepted by HESS journal, however the link (https://hess.copernicus.org/preprints/hess-2021-71/) that the authors provided does not show any accepted version of this paper (ONLY Preprint version is available so far, and preprint is NOT accepted version at all). Anyway, I did second-round review of this manuscript. Based on my review, I recommend that this manuscript is NOT applicable for publication in “Climate” journal. The reasons are as below:

1. Based on the Preprint of Dubois et al. [22] (https://hess.copernicus.org/preprints/hess-2021-71/ that the authors provided), the authors calibrated the HydroBudget model for the study area (36,000 km²) of southern Quebec, Canada based on three hypotheses. Among those hypotheses, the third hypothesis (i.e., the watershed response time is shorter than one month, thus compensating for the absence of water routing) is an absurd. The second hypothesis (i.e., the rivers drain unconfined aquifers) is not completely true.  The reason is that the river drains (a significant portion) unconfined aquifer during high river flow seasons; however, during low river flow seasons, unconfined aquifer drains/feeds the major portion to the river.  In the revised manuscript, the authors also mentioned that from May to November groundwater inflow into superficial (i.e., surface) water bodies (line 631-632), which represents that the second hypothesis is not completely correct. Since the model calibration was done based on two wrong hypotheses, the model outputs generated by this model for this study look questionable.
2. The second objective of this study was to identify controlling processes and thresholds of groundwater recharge (GWR) changes. However, the authors only highlighted the impact of meteorological variables (precipitation and temperature) on GWR changes as only controlling process. As we know that land use/land cover types significantly affect surface and subsurface hydrology (GWR here). In addition, soil types affect surface and subsurface hydrology (GWR). However, there is no evidence how land use and soil type variations affect GWR changes in the revised manuscript by using numerical values although the authors studied 8 watersheds in this study. This variation can be seen by comparing Fig 2(a), (b) of Dubois et al. [22] and Fig 9 of the revised manuscript between W7 and W8 watersheds, which receive same amount of mean annual precipitation and have similar mean annual temperature. The relationship of land use type, soil type along with precipitation and temperature with GWR changes would be complex, and it would take significant time to find this relationship. However, they only mentioned this issue qualitatively in Lines 574-583 and 601-604 of this manuscript by citing other articles. Similar concerns are given for determining thresholds of GWR changes (due to land use type and soil type variations along with precipitation and temperature changes). Therefore, the thresholds, which are provided in this study, do not represent the comprehensive guideline.
3. The authors addressed first and second major comments that I provided adequately. However, they did not address the third comment completely. They addressed and revised Introduction part nicely as per the comment. However, they did not response adequately when they were asked “How will the findings of this study be valid in other watersheds (which have different land use and soil types compared to this study) in cold and humid climatic regions around the world?” They addressed that “the results are expected to be comparable to other regions with similar climates in post-glacial geological environments and future climate change conditions” in Abstract Lines 26-28.  This explanation is not sufficient here because the thresholds of GWR changes they found in this study was based on having mainly coarse-grained soils in the unconfined aquifer. If any study area in cold and humid climatic region contains more fine-grained soils in the unconfined aquifer, the threshold for GWR changes that the authors mentioned would be higher and vice-versa (for having more coarse-grained soils than this study). Therefore, the findings is only applicable to this study area (36,000 km²) of southern Quebec, Canada.
4. To determine threshold for anything, it is necessary to consider all the factors and scenarios associated with the particular matter. For example, during determining drinking water guideline, public health authority set a specific threshold for a particular element considering all factors and scenarios associated with that element. Likewise, identifying thresholds of GWR changes under climate change conditions, all factors (i.e., at least land use type and soil type) and scenarios associated with GWR changes need to be considered. Therefore, examining one study area can not provide guideline in terms of thresholds of GWR changes to other study areas in cold and humid climatic regions around the world. Therefore, the title of this manuscript would provide wrong message to the reader. This study is a case study for this particular study area (southern Quebec, Canada). It can not be a general case study covering all cold and humid climatic regions around the world.

Based on the above-mentioned review, this manuscript is recommended to reject for publication in “Climate” journal. The authors are recommended to think their study as a regional case study for future publication. If they want to go for a general study (i.e., cold and humid climatic region), they need to resolve all the above-mentioned comments.

Reviewer 2 Report

I reviewed an earlier version of this manuscript and note that the authors have addressed many of the comments raised by reviewers. It's great to see that the underlying model has been published in HESS, allowing the resubmission to Climate to proceed and focus on the range of future climate scenarios and significance of groundwater recharge in this region.