A New Index to Assess the Effect of Climate Change on Karst Spring Flow Rate

Round 1

Reviewer 1 Report

The main question addressed by the research is to investigate the impact of climate change on karst springs' flow rate in the Zagros region under three CMIP6 scenarios (SSP1-1.9, SSP2-4.5, and SSP5-8.5).

Climate change is a very alarming situation nowadays and water supply is an important resource we have to care about. Then the manuscript is very important in this sense. Besides that, the topic is original or relevant in the field of global change and it t addresses some gaps in the field of sustainability. 

The research focuses on a specific type of aquifer (karstic) that is vulnerable to climate change. Investigating the impact on spring flow rates under different scenarios provides valuable insights into the hydrogeological response to climate change in this region.

The research adds value to the subject area by introducing a new index (𝐼𝑐𝑐) to assess the impact of climate change on spring flow rates. This novel approach, along with the consideration of various climate change scenarios, contributes to a better understanding of the complex interactions between climate change and karstic aquifers. The references are all appropriate till the topic results, but the discussion needs to be improved a lot.

Attached the manuscript with few yellow marks meaning that the phrase needs to be corrected (lines 117 and 118, 233, 408).

The figures and tables are both OK.

I would like to see again this manuscript with a nice and consistent discussion.

Comments for author File: Comments.pdf

Author Response

“The main question addressed by the research is to investigate the impact of climate change on karst springs' flow rate in the Zagros region under three CMIP6 scenarios (SSP1-1.9, SSP2-4.5, and SSP5-8.5).

Climate change is a very alarming situation nowadays and water supply is an important resource we have to care about. Then the manuscript is very important in this sense. Besides that, the topic is original or relevant in the field of global change and it t addresses some gaps in the field of sustainability. 

The research focuses on a specific type of aquifer (karstic) that is vulnerable to climate change. Investigating the impact on spring flow rates under different scenarios provides valuable insights into the hydrogeological response to climate change in this region.

The research adds value to the subject area by introducing a new index (???) to assess the impact of climate change on spring flow rates. This novel approach, along with the consideration of various climate change scenarios, contributes to a better understanding of the complex interactions between climate change and karstic aquifers. The references are all appropriate till the topic results, but the discussion needs to be improved a lot.

Attached the manuscript with few yellow marks meaning that the phrase needs to be corrected (lines 117 and 118, 233, 408).

The figures and tables are both OK.

I would like to see again this manuscript with a nice and consistent discussion.”

Responses: Many thanks for the thoughtful comments; below is the explanations to them and the lines are where the clarification has been done.

Corrected in comparison to original lines 117 and 118, 233, 408:

Lines 118-120:

On the other hand, approaches of lumped parameter modeling and of statistical basis offer solutions with less data (parameter) demand.

 Lines 239-244:

Three sequence steps of the study are (1) downscaling the GCMs climate output with LARS-WG6, (2) time series analysis using CCF as well as covariance function, (3) introducing new index. The first step is to predict future precipitation; in the second one the relation between the precipitation and springs flow rate in the historical period is investigated. In the third step, based on such relationship and predicted precipitation, the climate change impact on spring flow rate is studied.

Lines 429-431:

Fig. 7 shows the sum of differences between spring discharge at any time and its average (d) in the historical period (baseline) and in near future (2050-2021) and far future (2080-2051) under SSP1-1.9, SSP2-4.5 and SSP5-8.5.

Discussion improvement:

Lines 388-400:

Generally, precipitation increases under SSP1-1.9 scenario and decreases under SSP2-4.5 while it both decreases and increases under SSP5-8.5 scenario. The northern part, in terms of precipitation reduction, is affected by climate change to a lesser extent than the southern part under SSP2-4.5. On the contrast, under SSP5-8.5 southern part of Zagros suffers no precipitation reduction. Kuhrang in the central parts is affected the most particularly from 2051-2080 under SSP2-4.5. On the whole, the annual aver-age precipitation of all 14 stations in the baseline is 540 mm/y but in the first and sec-ond 30-year periods under SSP1-1.9 it increases to 665 and 691 mm/y, under SSP2-4.5 it endures reduction and becomes 504 and 484 mm/y, and under SSP5-8.5 it experiences a 13 mm/y rise (553 mm/y) and a 6 mm/y drop (534 mm/y), respectively. The corresponding percentage in the first and second 30-year periods under SSP1-1.9 is 24% and 28% increase, under SSP2-4.5 is 6% and 9% reduction, and under SSP5-8.5 is 3% in-crease and less than 1% reduction, respectively. 

Lines 439-445:

Pirghar with a decrease of (-0.085) has the largest decrease in flow rate and Tudezan with a decrease in of (-0.018) has experienced the lowest decrease in the flow rate. Therefore, the two springs of Pirghar and Bernaj, which show the most changes in the historical period and in all the future scenarios, are the most karstified springs contrasted to the two springs of Tudezan and Cureh which have the lowest degree of karstification. The other springs are in the range between these two end-members of low and high degree of karstification (low to high karstified springs: Sasan, Sarabgarm, Dimeh, Barm, Tangsiab and Biston).

Lines 525-539:

4.4. limitations and uncertainties

Data requirement in long term measurements and the interval of monitoring particularly for karst spring discharge is a challenge. In fact, in order to calculate the co-variance function so that it is safe to assume that it stays constant in future, requires such measures. On the other hand, the assumption on which the covariance function between rainfall and karst system stays constant in near future is conceivable but it is uncertain in far future. Another constrain is the necessity that the weather station site should be within the spring catchment area. Moreover, downscaling technique and the number of global circulation models (GCMs) are other uncertainty sources of such studies. Although, multi-model ensemble of Coupled Model Inter-comparison Project phase 6 (CMIP6) were used to resolve the shortcomings of an individual GCM, the ad-equate number of GCMs is unknown; see Raju and Kumar (2020) and Wang et al. (2020) for more details. To overcome such limitation and uncertainties the springs and stations with enough data having acceptable monitoring intervals and 37 GCMs were selected. Quantification the extent of such uncertainties with mitigation strategies are suggested for future research.

Reviewer 2 Report

Recommendations:

While the paper is comprehensive, a few recommendations for improvement include:

Providing additional context on the limitations and uncertainties associated with the proposed methodology.

Overall, the paper makes a valuable contribution to the understanding of climate change impacts on karstic aquifers, presenting a well-structured methodology and introducing a novel index for assessing such impacts.

The paper is well writen.

Author Response

“While the paper is comprehensive, a few recommendations for improvement include:

Providing additional context on the limitations and uncertainties associated with the proposed methodology.

Overall, the paper makes a valuable contribution to the understanding of climate change impacts on karstic aquifers, presenting a well-structured methodology and introducing a novel index for assessing such impacts.”

Responses: Many thanks and appreciations for the thoughtful comments; below is the explanations to them and the lines are where the future discussion has been implemented in the article.

Lines 525-539:

4.4. limitations and uncertainties

Data requirement in long term measurements and the interval of monitoring particularly for karst spring discharge is a challenge. In fact, in order to calculate the covariance function so that it is safe to assume that it stays constant in future, requires such measures. On the other hand, the assumption on which the covariance function between rainfall and karst system stays constant in near future is conceivable but it is uncertain in far future. Another constrain is the necessity that the weather station site should be within the spring catchment area. Moreover, downscaling technique and the number of global circulation models (GCMs) are other uncertainty sources of such studies. Although, multi-model ensemble of Coupled Model Inter-comparison Project phase 6 (CMIP6) were used to resolve the shortcomings of an individual GCM, the adequate number of GCMs is unknown; see Raju and Kumar (2020) and Wang et al. (2020) for more details. To overcome such limitation and uncertainties the springs and stations with enough data having acceptable monitoring intervals and 37 GCMs were selected. Quantification the extent of such uncertainties with mitigation strategies are suggested for future research.

Reviewer 3 Report

This paper is clearly written and it is interesting for publishing in this journal because of its topic and new information about climatic condition in mentioned area. My recommendation for further analysis is the application of partial correlation function for one complete advanced approach. So the literature will be extended by the newest papers dealing with this topic. 

There is one rather confused sentence in line 420-421....copy paste error probably

This paper is clearly written and it is interesting for publishing in this journal because of its topic and new information about climatic condition in mentioned area. My recommendation for further analysis is the application of partial correlation function for one complete advanced approach. So the literature will be extended by the newest papers dealing with this topic. 

There is one rather confused sentence in line 420-421....copy paste error probably

Author Response

“This paper is clearly written and it is interesting for publishing in this journal because of its topic and new information about climatic condition in mentioned area. My recommendation for further analysis is the application of partial correlation function for one complete advanced approach. So the literature will be extended by the newest papers dealing with this topic.”

Responses:

We greatly appreciate the suggestion for the application partial correlation function. In fact, autocorrelation function (PACF) was used for the main ten springs although not implemented in this paper; partial autocorrelation was highest at lag 1 and statistically significant for nine of the springs indicating an autoregressive model with order 1. Partial correlation function is also set to apply in a follow up research. In this perspective, we have some other research under consideration with artificial intelligence methodology in which PACF is implemented and partial correlation function would be applied.

“There is one rather confused sentence in line 420-421....copy paste error probably”

The sentences structure is improved in a way to convey the intended message (lines 439-445:):

Therefore, the two springs of Pirghar and Bernaj, which show the most changes in the historical period and in all the future scenarios, are the most karstified springs contrasted to the two springs of Tudezan and Cureh which have the lowest degree of karstification. The other springs are in the range between these two end-members of low and high degree of karstification (low to high karstified springs: Sasan, Sarabgarm, Dimeh, Barm, Tangsiab and Biston).

Reviewer 4 Report

The paper explores the vulnerability of karstic aquifers to climate change, choosing ten springs in the Zagros region of Iran as study sites. The paper presents noteworthy findings through time series and trend analysis. The introduction of the Icc index, which considers both the karst system and precipitation changes, is a novel aspect of the study. Generally, the paper is well organized. The authors introduce that one of the main objectives is to use the trend analysis, however, no specific method for trend analysis is described in the "Methodology" section. Also in the "Results" section, the analysis for trends is very descriptive. Therefore, moderate revision should be conducted before it could be considered for publishing. Additionally, the English should be polished before re-submission. The detailed comments are provided below.

In the abstract, it is suggested to clarify the full names and explain the new proposed indices.

Lines 117-120: is the needed amount of data less when using the lumped parameter modeling? what is the main findings by Labat et al.? Please make them clear.

Line 150-151: it's better to make it clear that "the impact of climate change" on hydrogeological condition (or spring rate) is rarely reported.

Lines 169-170: for objective (a), it is senseless to just "use" the time series analysis and covariance function. You should imply what insights you want to obtain through these methodologies.

Fig. 3: Please add the meaning of triangles in the legend.

The references are outdated, of which most are papers published before 2010. Therefore, more recent publications should be cited.

The format should be improved to meet the journal's standard. For example, the number of equations should be put on the rightest side of each row; the font should be kept the same for all figures;

English should be improved.

Author Response

“The paper explores the vulnerability of karstic aquifers to climate change, choosing ten springs in the Zagros region of Iran as study sites. The paper presents noteworthy findings through time series and trend analysis. The introduction of the Icc index, which considers both the karst system and precipitation changes, is a novel aspect of the study. Generally, the paper is well organized. The authors introduce that one of the main objectives is to use the trend analysis, however, no specific method for trend analysis is described in the "Methodology" section. Also in the "Results" section, the analysis for trends is very descriptive. Therefore, moderate revision should be conducted before it could be considered for publishing. Additionally, the English should be polished before re-submission. The detailed comments are provided below.”

Many thanks for your constructive questions and comments which have surly improved the quality of the article. Below is our responses:

Response to the well asked comments on the trend analysis:

Lines 245-247:

The linear model type was applied to the time series of both target variables (i.e. rainfall and spring discharge) in trend analysis to determine whether such variables have undergone any change.

In the abstract, it is suggested to clarify the full names and explain the new proposed indices.

lines 19 to 21:

  is variability of spring discharge from past to future,  is spring discharge variability over the historical data and  is effect of precipitation and spring discharge change together.

Lines 117-120:

is the needed amount of data less when using the lumped parameter modeling? what is the main findings by Labat et al.? Please make them clear.

Lines 118-123:

On the other hand, approaches of lumped parameter modeling and of statistical basis offer solutions with less data (parameter) demand. Labat et al. (2000 a, b) used correlation stochastic processes to investigate the rainfall and karst spring relationship. They concluded that wavelet analyses approach outperforms the linear-based relation of input- output models (i.e. rainfall-runoff) in karst systems which noticeably show non-stationary non-linearity behavior.

Line 150-151: it's better to make it clear that "the impact of climate change" on hydrogeological condition (or spring rate) is rarely reported.

Lines 156-158:

So far and to the knowledge of the authors, the impact of climate change on hydrogeological conditions in karstic regions in Iran is rarely reported.

Lines 169-170: for objective (a), it is senseless to just "use" the time series analysis and covariance function. You should imply what insights you want to obtain through these methodologies.

Lines 175-177:

In this study, the objectives: are a) to use time series analysis and covariance function in the historical period and future to characterize karst aquifer system b) to introduce new indices to evaluate the impact of climate change on the karstic springs flow rate.

Fig. 3: Please add the meaning of triangles in the legend.

Line 365:

The triangle is to show the water table; this marker is added onto the blue dash line to fulfill this purpose:

The references are outdated, of which most are papers published before 2010. Therefore, more recent publications should be cited.

Of the references 25 are more recent (i.e. 2010). We added three more recent articles to strengthen the discussion and weight the side of  the more updated references:

Lines 140-142:

Time series analysis can also be used to drive rainfall intensity and time lag curve which reveal valuable information on spring response and karst segments (Martín-Rodríguez et al., 2023).

Martín-Rodríguez, J.F., Mudarra, M., De la Torre, B. and Andreo, B., 2023. Towards a better understanding of time-lags in karst aquifers by combining hydrological analysis tools and dye tracer tests. Application to a binary karst aquifer in southern Spain. Journal of Hydrology, 621, p.129643.

Lines 532-536:

Although, multi-model ensemble of Coupled Model Inter-comparison Project phase 6 (CMIP6) were used to resolve the shortcomings of an individual GCM, the adequate number of GCMs is unknown; see Raju and Kumar (2020) and Wang et al. (2020) for more details.

Raju, K.S. and Kumar, D.N., 2020. Review of approaches for selection and ensembling of GCMs. Journal of Water and Climate Change, 11(3), pp.577-599.

Wang, H.M., Chen, J., Xu, C.Y., Zhang, J. and Chen, H., 2020. A framework to quantify the uncertainty contribution of GCMs over multiple sources in hydrological impacts of climate change. Earth's Future, 8(8), p.e2020EF001602.

The format should be improved to meet the journal's standard. For example, the number of equations should be put on the rightest side of each row; the font should be kept the same for all figures;

The number of equations are put on the end side of the corresponding row. The descriptive text font in the figures are set in a way to be easily readable.

Round 2

Reviewer 1 Report

The authors made substantial changes to the manuscript and most of the suggestions were accepted, improving the quality of the article to be published

Reviewer 4 Report

The paper has been greatly improved. I agree it to be published in sustainability.