Assessment of Run-of-River and Hydropower Plants in Peru: Current and Potential Sites, Historical Variability (1981–2020), and Climate Change Projections (2035–2100)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The following comments are quite the same as the attached PDF file. Please read the PDF file if the format of this comment may be inadequate.

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Review
This manuscript addresses the present and future estimation of hydropower plants
(HPP) and run-of-river plants (RoR) in Peru using the ARNOVIC hydrological
model. Before the hydrological simulations, the authors detect the potential
RoR sites out of the restriction zones in Peru using GIS, in addition to the
operational+planned HPP sites. The ARNOVIC model needs daily forcing data
of precipitation and evapotranspiration, which is obtained from daily temperature
using Hargreaves-Samani equation. As historical (1981-2020) and future (2035-
2065 and 2071-2100 for SSP1-2.6, SSP3-7.0, SSP5-8.5) datasets, the authors use
the BASD-CMIP6-PE, which are statistically downscaled daily precipitation
and temperature based on 10 GCMs’ outputs in CMIP6. As a reference of
daily precipitation, temperature, and streamflow in the historical real world,
they use the Peruvian Interpolated data of the SENAMHI’s Climatological and
Hydrological Observations (PISCO). The authors show both future HPP and
RoR are projected to decrease in many regions, compared with the baseline
period of 1981-2010(2020?) with future time slices of 2035-2065 and 2071-2100
under SSP1-2.6, SSP3-7.0, and SSP5-8.5 emission scenarios.
I recommend that this paper be accepted after some revisions. I believe that this
paper becomes more useful and valuable study after the authors add more explanations
to clarify your understanding and interpretation without any confusion
and misunderstanding.
Major comments:
The authors show only the percentile changes of hydroelectric parameters in
future simulations compared with the historical simulations. They do not show
the increases and decreases of simulated CR (MW), EF and EP (GWh) parameters
as the numbers in any Figures, Tables nor texts. While the absolute value
changes of CR, EF and EP are very useful for the stakeholders, the differences
between future and historical period simulations have large bias because of
the large differences between observed and simulated historical parameters, as
shown in Figure 7. How should the stakeholders interpret the percentage change
in this paper as the absolute increases and decreases? The stakeholders will
need the information how large and many HPPs and RoRs will be required in
future. Could you show or suggest how to recognize the absolute changes from
the percentage change? Then this article will become more valuable for the
stakeholders. If the authors show only the percentage changes in this study, the
absolute change estimation may become future works.
The authors show mainly SSP1-2.6 and SSP5-8.5 scenarios in future compared
with the baseline. On the other hand, the description for SSP3-7.0 is quite small
in main text. There are larger changes in SSP3-7.0 than SSP1-2.6 and SSP5-8.5
scenarios in many parameters, future periods, and regions in this study. Could
you interpret such strange behavior of SSP3-7.0? Shiogama et al (2023, Nature
Climate Change) show how SSP3-7.0 is different from the other SSP emission scenarios. I don’t know the difference can explain the SSP3-7.0 behaviour in
Peru in your study. But I recommend you to consider the SSP3-7.0 behaviour
with Shiogama et al (2023). Removing SSP3-7.0 simulations and analyses from
this paper is one way to simplify your message.
Tables 6-7 and Figures 8-11 in 3.3 Future hydropower assessment:
The authors should explain clearly how to compute the 20th, 50th and 80th
percentiles in this subsection. I think that Figures 9 and 11 shows differences
between the 50th percentile values for historical (30 years * 10 GCMs = 300
samples) and future climates (300 samples) for each site. If so, “hot model”
problem may distort this study results. Please check the 50th percentile value
changes between historical (30 years * 1 GCM) and future climate for each site
and each GCM, and compare 10 GCM results for each other to check robustness
of Figures 9 and 11. Moreover, the area averaged cases (Tables 6-7 and Figures
8 and 10) are more difficult to interpret the results. The percentile values (20th,
50th and 80th) are computed using all the samples in one region (30 years * 10
GCMs * number of sites) for historical and future climates, then the difference
is computed between historical and future climates? The percentage changes of
50th percentiles shown in Figures 9 and 11 are area-averaged as in Tables 6-7
and Figures 8 and 10? . . . or something else? Without such definition of the
percentage changes of percentile values shown in your study, the readers can not
recognize your results correctly.
The above comments may come from my misunderstanding of your figures
and main text. Please explain your interpretation more carefully without any
confusion.
Minor comments:
• historical period is 1981-2010 (30 years) or 1981-2020 (40 years)? The
former is shown in L13, L181, L322, L327, L408, L439, Figures 8-11, and
the latter in title, L9, L170, Figures 3-7. If the former 30-year case is enough
to show your message, please use the former period for easy-understanding.
• 2050s period is 2035-2065 (31 years) or 2036-2065 (30 years)? The former
is shown in title and L15, and the latter in L182, L334, Figures 8-11. The
latter is better due to the same length (30 years) of periods in baseline
and 2 future timeslices.
• Figure 1 and related statements: Please note the letters “a” to “c” for the
panels in Figure 1, and distinguish them in the related statements. Figure
1 in L112 should be written as Figure 1a. Figure 1 in L130 and L243
should be written as Figure 1c. Figure 1 in L209 is Figure 1b? The colored
circles as CON and PLA may be difficult to distinguish for each other in
the middle panel of Figure 1. Take care of such identification problem.
Which panel is noted as Figure 1 in L120? If possible, Figure 1b and 1c
should be swapped due to their order in the main text (Such order issues are found in the following Figures and Tables in main part and appendix).
L104-112: Please clarify the relationship between 3 hydrographic basins
(BP, BT, BA, not related after here. . . required?) and 6 regions (PFS, PFN,
ALN, ALC, ALS and TIC) in Figure 1a. BP=PFN+PFS?, BT=TIC?,
BA=ALN+ALC+ALS? or not?
• Figure 2: Please use upper/lower letters appropriately. The box “Simulated
flow” should be placed at both in “Historical parameters” and “Future
projection” rows? The boxes “Historical simulated” and “Future simulated”
should be written as “Simulated historical” and “Simulated future”? “Head
net” should be written as “Net head” in Figure 2 and Table 1?
• Table 4 and related statements: Too many values are listed in Table 4, but
most of them are not explained. Why Min and Max have a symbol “”’?
What is shown in the last row in English? Omit unnecessary rows and
columns. L349: “. . .was estimated at 94.1GW (Table 4). . . ” but I can
not find the value in Table 4. How can we derive the value using Table 4?
Please check such insufficient descriptions in this article.
• Table 5 and related statements: What is shown for HPP and RoR by region
. . . add “The numbers of” before “Hydropower and . . . ”. If the 6 regions in
Table 5 (“Pacific South” to “Titicaca”) means 6 regions in Figure 1a (PFN
to TIC), the latter notation is ennough and less missunderstanding. What
means “LAC” in L361-362? . . . typo of “ALC”? While the numbers of
HPP are distinguished between “operational” and “planned”, the numbers
of RoR are not. All of RoR is just planned now? . . . or “operational” and
“planned” RoR are mixed? Such clasification of HPP and RoR should be
explained more clearly before.
• Figures 3-4 and related statements: Please note the letters “a” to “c” for
the panels in Figures 3-4.
• Figures 5 and 6 and related statements: At least, CR and EF (1st and 2nd
column) in PFN (2nd row) show decrease trends in Figure 5, but the box
colour is blue. These are correct? How about some of other panels not
only in Figure 5 but also in Figure 6? L379-380: “All the hydro-energy
parameters of the six regions. . . ” but only five regions are shown in Figure
5. Where is 6th region of TIC in Figure 5? Format of Figures 5 and 6
are similar (except for TIC panels), but the gray shades are shown only
in Figure 6. Please explain these gray shades in Figure 6. Why the gray
shades are not shown in Figure 5?
• Figure 7: Please explain the solid blue and dashed black lines in 3 panels.
Figure 7 shows the hydro-energy parameter simulations using statistically
downscaled 10 GCM outputs tend to underestimate in historical period.
Computing such relations for the sub-basins in each GCM historical output
may be useful for the bias correction of the percentage changes in future
climate scenarios.

• Figures A1-A2: Add graphical colour legend in or beside of Figures to
help easy-understanding. Especially, it is necessary in Figure A2 because
of many colour classification. Light green should be change into easierdistinguish
colour from white “no restriction area” in Figure A2. If whete
areas in Figure 1c are consistent and equal to those in Figure A2, it may
be enough to replace Figure A2 instead of Figure 1c.
What’s “PH” in L417, L437 and L462? What’s “ICN” in L432? Please check
such abbreviation without explaining.
I hope these comments will be helpful to improve this paper.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The notations of SSP scenarios are not consistent in this article as follows: 1) SSPa-b.c, 2) SSPa.b-c, and 3) SSPa.b.c. (a, b, c show digits). I recommend the notation of 1), for example SSP1-2.6, SSP3-7.0 and SSP5-8.5, as used in this abstract and IPCC reports.

"Head net" should be written as "Net head" in Figure 2 and Table 1?

"hydro-energy" or "hydroenergy"

Some figures and tables are not written in English:

• "Scenary" at the 3rd column's head in Tables 6 and 7 should be written as "Scenario"?
• Head row of Table A2.
• Head row and last column of Figure A1.

Author Response

Summary

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files.

 

Minor comments

Comments 1: Historical period is 1981-2010 (30 years) or 1981-2020 (40 years)? The former is shown in L13, L181, L322, L327, L408, L439, Figures 8-11, and the latter in title, L9, L170, Figures 3-7. If the former 30-year case is enough to show your message, please use the former period for easy-understanding.

Response 1: Thanks for the comments, your suggestion is much appreciated. We detailed that historical period is 1981-2020 (40 years), this period is analysed in section “Historical hydropower assessment” using “observed historical data”. On the other hand, in section “Future hydropower assessment” reference period to evaluate future projection is between 1981-2010 (30 years) from “simulated historical data”, because historical period from BASD-CMIP6-PE is until 2014. We included a new sentence in the Revised Manuscript (RM), section Overview: “We defined the hydropower potential for historical period (1981-2020) for HPPs and RoRs. At last, we generated a series of future projections for hydropower potential, based on the percentage change between the parameters of a reference period (1981-2010) and those of medium-term (2036-2065) and long-term (2071-2100) future periods from an ensemble of statistically downscaled CMIP6 climate scenarios.”

Comments 2: 2050s period is 2035-2065 (31 years) or 2036-2065 (30 years)? The former is shown in title and L15, and the latter in L182, L334, Figures 8-11. The latter is better due to the same length (30 years) of periods in baseline and 2 future timeslices.

Response 2: Thank you for your valuable comment. The period 2050s is between 2036-2065, the necessary changes have been implemented throughout the abstract to homogenize that period. In the RM, see abstract: “The main results about capacity indicated that operational hydroelectric plants (Run-of-River plants) are projected to decrease by -2.8 to -5.2\% (-1.2 to -6.6%) during 2036-2065 and...”.

Comments 3: Figure 1 and related statements: Please note the letters “a” to “c” for the panels in Figure 1, and distinguish them in the related statements. Figure 1 in L112 should be written as Figure 1a. Figure 1 in L130 and L243 should be written as Figure 1c. Figure 1 in L209 is Figure 1b? The colored circles as CON and PLA may be difficult to distinguish for each other in the middle panel of Figure 1. Take care of such identification problem. Which panel is noted as Figure 1 in L120? If possible, Figure 1b and 1c should be swapped due to their order in the main text (Such order issues are found in the following Figures and Tables in main part and appendix). L104-112: Please clarify the relationship between 3 hydrographic basins (BP, BT, BA, not related after here. . . required?) and 6 regions (PFS, PFN, ALN, ALC, ALS and TIC) in Figure 1a. BP=PFN+PFS?, BT=TIC?, BA=ALN+ALC+ALS? or not?

Response 3: Thanks for your comments. Figure 1 has been redrawn to edit the numeration, arrangement, and reference of subfigures. Subfigure 1c, was edited for better visualization. Additionally, the regions' and basins' relation is explained in the last sentence. Relation “BP=PFN+PFS?, BT=TIC?, BA=ALN+ALC+ALS” is right, now we deleted acronyms for basins. In RM, section Study Area the Figure 1 is edited.

Comments 4: Figure 2: Please use upper/lower letters appropriately. The box “Simulated flow” should be placed at both in “Historical parameters” and “Future projection” rows? The boxes “Historical simulated” and “Future simulated” should be written as “Simulated historical” and “Simulated future”? “Head net” should be written as “Net head” in Figure 2 and Table 1?

Response 4: We appreciate your detailed remark and have adjusted the manuscript to apply your recommendation. In Figure 2 and Table 1, we edited capital letters and rewrote word boxes. Moreover, the box “simulated flow” is now located in the “Historical Parameters” row; only “Simulated future” from “Parameters hydroenergy” is in the “Future projection” row. In RM, section Overview the Figure 2 is edited.

Comments 5: Table 4 and related statements: Too many values are listed in Table 4, but most of them are not explained. Why Min and Max have a symbol “”’? What is shown in the last row in English? Omit unnecessary rows and columns. L349: “. . .was estimated at 94.1GW (Table 4). . . ” but I can not find the value in Table 4. How can we derive the value using Table 4? Please check such insufficient descriptions in this article.

Response 5: Thanks, your comment is well taken. We have made the correction as recommended. in Table 4, the column and row names Mín, Máx, Nº ríos/sitios are replaced to, Min, Max, Nº subbasins, and Nº sites. Moreover, the amount and classifications data on theoretical capacity were reduced and detailed by column. To refer to L349 as edited, “... these sub-basins add up to a potential theoretical capacity of 91.7 GW”. In RM, section Potential Hydropower Sites, Table 4 is edited.

Moreover, to explain Table 4, we added in RM: “For a more detailed description of the hydropower potential, the following cases were analysed (Table 5). a) All sub-basins excluding restricted zones, b) sites identified with capacity up to 100 MW, c) sites identified with capacity up to 20 MW, d) sites identified with capacity up to 1 MW (mini-HPP), and e) sites identified with capacity from 1 to 20 MW (small-HPP). Sites with capacity below 0.1 MW were excluded, because their total capacity is insignificant with respect to the national total (less than 0.2 %).”

Comments 6: Table 5 and related statements: What is shown for HPP and RoR by region . . . add “The numbers of” before “Hydropower and ...”. If the 6 regions in Table 5 (“Pacific South” to “Titicaca”) means 6 regions in Figure 1a (PFN to TIC), the latter notation is ennough and less missunderstanding. What means “LAC” in L361-362? . . . typo of “ALC”? While the numbers of HPP are distinguished between “operational” and “planned”, the numbers of RoR are not. All of RoR is just planned now? . . . or “operational” and “planned” RoR are mixed? Such clasification of HPP and RoR should be explained more clearly before.

Response 6: We appreciate your insightful observation and have updated Table 5 accordingly. The title of table was edited and now is “The numbers of Hydropower and Run-of-River plants by region”, and their names for regions are listed by acronyms. LAC refers to ALC, now both is ALC to standardize terms. The number of HPP and RoR were distinguished and explained as plannified and operational. In that sense all RoRs are defined as off-grid power plants plannified. In RM, section Potential Hydropower Sites the Table 5 is edited.

Comments 7: Figures 3-4 and related statements: Please note the letters “a” to “c” for the panels in Figures 3-4.

Response 7: Thank you for your observations; Figures 3 and 4 now include and refer to subfigures “a” to “c”. In RM, section Historical Hydropower Assessment the Figures 3 is edited.

Comments 8: Figures 5 and 6 and related statements: At least, CR and EF (1st and 2^nd column) in PFN (2nd row) show decrease trends in Figure 5, but the box colour is blue. These are correct? How about some of other panels not only in Figure 5 but also in Figure 6? L379-380: “All the hydro-energy parameters of the six regions. . . ” but only five regions are shown in Figure 5. Where is 6th region of TIC in Figure 5? Format of Figures 5 and 6 are similar (except for TIC panels), but the gray shades are shown only in Figure 6. Please explain these gray shades in Figure 6. Why the gray shades are not shown in Figure 5?

Response 8: Thank you for pointing out these observations. Indeed, Figures 5 and 6 have a continuous blue line as a linear reference model, we have suppressed this element because of its discordance with the statistics described as Sen's slope, which already indicate the decadal rate of change of each variable. On the other hand, the text to refer to Figure 5 was edited because only five regions have operational HPPs according to Table 5. Moreover, gray shades around solid lines were deleted because they only refer to the limits of the 0.3 and 0.7 percentiles of each group of RoR or HHP according to their hydro-energetic parameters. In RM, section Trends the Figures 5 is edited.

Comments 9: Figure 7: Please explain the solid blue and dashed black lines in 3 panels. Figure 7 shows the hydro-energy parameter simulations using statistically downscaled 10 GCM outputs tend to underestimate in historical period. Computing such relations for the sub-basins in each GCM historical output may be useful for the bias correction of the percentage changes in future climate scenarios.

Response 9: Thank you for highlighting this issue. The necessary changes have been implemented in Figure 7, their caption was edited to detail blue and black line, both refers to correlation and 1:1 ratio, respectively. Both datasets were evaluated with the hydro-energy parameters estimated with equations in Table 3 based on the observed flows from the PISCO-HyD-ARNOVIC model (simulated) and from the annual averages recorded by COES (observed). The hydro-energy parameters based on the median of 10 GCMs were used to evaluate future projections. In RM, section Statistical Assessment the Figures 7 is edited.

Comments 10: Figures A1-A2: Add graphical colour legend in or beside of Figures to help easy-understanding. Especially, it is necessary in Figure A2 because of many colours classification. Light green should be change into easier distinguish colour from white “no restriction area” in Figure A2. If white areas in Figure 1c are consistent and equal to those in Figure A2, it may be enough to replace Figure A2 instead of Figure 1c.

Response 10: Thank you for your comments, and we agree with you. Legends and color reassignments were added to Figure A1 for suitable visual differentiation from the background. Additionally, to group the information presented, Figure A2 replaced Figure 1c, new version of this Figure has already been presented and described above. In appendix of RM, the Figures A1 is edited.

Comments 11: What’s “PH” in L417, L437 and L462? What’s “ICN” in L432? Please check such abbreviation without explaining.

Response 11: Thank you for your suggestion and we have updated the text accordingly, terms “PH” and “ICN”, were replace with “Hydro-energy Parameters” and “Installed Capacity”, both terms were explained in this article. In the RM section Future Hydropower Assessment now is: “... It is relevant to mention that the Central Atlantic region, where the set of HPPs with the highest CR is located (52.7 and 59.2 \% of the total operational and planned, respectively),...”.

 

Major comments

Comments 12: The authors show only the percentile changes of hydroelectric parameters in future simulations compared with the historical simulations. They do not show the increases and decreases of simulated CR (MW), EF and EP (GWh) parameters as the numbers in any Figures, Tables nor texts. While the absolute value changes of CR, EF and EP are very useful for the stakeholders, the differences between future and historical period simulations have large bias because of the large differences between observed and simulated historical parameters, as shown in Figure 7. How should the stakeholders interpret the percentage change in this paper as the absolute increases and decreases? The stakeholders will need the information how large and many HPPs and RoRs will be required in future. Could you show or suggest how to recognize the absolute changes from the percentage change? Then this article will become more valuable for the stakeholders. If the authors show only the percentage changes in this study, the absolute change estimation may become future works.

Response 12: Thank you for highlighting the importance of clear definitions in our study. According to various studies (Tobias et al., 2023; Stucchi et al., 2023; Trancoso et al., 2024), it is advisable to present future projections as a range of percentage-based outcomes relative to a reference period (1981–2010). This approach accounts for model biases and the scale of analysis used in this study, thereby necessitating a cautious interpretation of the results. Figure 7, as referenced in “Minor Comments IX”, estimates the correlation between observed data (COES records) and simulated results (derived from the methodology presented) for hydro-energy parameters. The uncertainty analysis of these findings is detailed in the Discussion section, primarily attributing variations to technical considerations related to system efficiency and the operational rules governing existing hydropower plants.

To enhance the accessibility and comprehension of these results for stakeholders, the percentage change in future projections, alongside historical values, is available through a web-based application (indicated in the Data Availability section). This platform visualises future projections for each RoR (Run-of-River) and HPP (Hydropower Plant). While general demand-related information is outlined in the Introduction, a comprehensive national strategy for addressing regional energy deficits remains undefined. Furthermore, the assessment of absolute changes in hydro-energy parameters is identified as a subject for future research. We hope that with these comments we have answered your question. In the RM section Methods, now is: “The future projection is based on the percentage of change (Bosshard et al., 2011, Savelsberg et al., 2018) in hydro-energy parameters between the future period (2036-2065 and 2071-2100) and the reference period (1981-2010); for both periods, the parameters are the averaged over a period of 30 years (Jung et al., 2021, Baniya et al., 2024, Chuphal et al., 2023, Stucchi et al., 2023, Tobias et al., 2023).”

Comments 13: The authors show mainly SSP1-2.6 and SSP5-8.5 scenarios in future compared with the baseline. On the other hand, the description for SSP3-7.0 is quite small in main text. There are larger changes in SSP3-7.0 than SSP1-2.6 and SSP5-8.5 scenarios in many parameters, future periods, and regions in this study. Could you interpret such strange behavior of SSP3-7.0? Shiogama et al (2023, Nature Climate Change) show how SSP3-7.0 is different from the other SSP emission scenarios. I don’t know the difference can explain the SSP3-7.0 behaviour in Peru in your study. But I recommend you consider the SSP3-7.0 behaviour with Shiogama et al (2023). Removing SSP3-7.0 simulations and analyses from this paper is one way to simplify your message.

Response 13: Thanks for your comment regarding the analysis of uncertainty in our assessment of future projection. Greater emphasis has been placed on describing the results derived from the SSP1 and SSP5 scenarios, as they represent the minimum and maximum projected changes. However, the analysis has now been expanded to include SSP3, detailed in the Future Projections Assessment section. Following the recommendations outlined in Shiogama (2023), discussions have been enhanced to address uncertainties in the future projections based on simulations under the SSP3 scenario. These three scenarios were selected as they are the ones available in the BASD-CMIP6-PE dataset, which contains calibrated models for the study area. Presenting the estimated biases across all three scenarios is crucial for understanding the uncertainties associated with Global Climate Models (GCMs) in hydro-energy parameter estimations. Nonetheless, the deficiencies identified within SSP3 are specifically highlighted in the Conclusions section of this study. First, in the RM section Discussions, now is: “..., for this reason, it is important to develop a hydrological model of higher resolution in the disaggregation of sub-basins, include regional GCMs for the analysis of future projection and the improvement of digital elevation models to increase the representativeness of the longitudinal profiles of the rivers (Almazroui et al., 2021, Bista et al., 2021).”

Second, in the RM section Discussions, now is: “Additionally, recently SSP3-7.0 received increased attention due to leading to the warmest climate scenarios (Shiogama et al., 2023), Our results coincide with these observations, since, in the regions analysed and mainly for the period 2050s, higher rates of decrease and lower increase rates are observed for all hydro-energy parameters (Table 6 and 7).”

Comments 14: Tables 6-7 and Figures 8-11 in 3.3 Future hydropower assessment: The authors should explain clearly how to compute the 20th, 50th and 80th percentiles in this subsection. I think that Figures 9 and 11 shows differences between the 50th percentile values for historical (30 years * 10 GCMs = 300 samples) and future climates (300 samples) for each site. If so, “hot model” problem may distort this study results. Please check the 50th percentile value changes between historical (30 years * 1 GCM) and future climate for each site and each GCM, and compare 10 GCM results for each other to check robustness of Figures 9 and 11. Moreover, the area averaged cases (Tables 6-7 and Figures 8 and 10) are more difficult to interpret the results. The percentile values (20th, 50th and 80th) are computed using all the samples in one region (30 years * 10 GCMs * number of sites) for historical and future climates, then the difference is computed between historical and future climates? The percentage changes of 50th percentiles shown in Figures 9 and 11 are area-averaged as in Tables 6-7 and Figures 8 and 10? . . . or something else? Without such definition of the percentage changes of percentile values shown in your study, the readers can not recognize your results correctly.

Response 14: Thank you for this detailed feedback on our Figures and Tables. The estimation process for the 20th, 80th, and 50th percentiles (median) of future projections from the 10 GCMs has been described in greater detail in the section Methods from the RM: "Therefore, the outputs of the 10 GCMs were summarized in three series of hydrological references, taking into account the extreme scenarios proposed by COES. This choice is based on the 20th and 80th percentiles \% of the 10 streamflow series grouped by each scenarios and period, to refer to extremely wet and dry years, respectively."

In this sense, a single projection value is obtained by averaging the 30-year reference period and the future horizon, yielding six values per site for each RoR (Run-of-River) or HPP (Hydropower Plant), this values is showed in web aplication (section Data Availability). The influence of extreme values, potentially linked to hot model variations, is mitigated through the use of selected percentiles. An analysis of precipitation and temperature projections comparing reference and future periods (based on 30-year averages by GCMs) has been added in Figure S03 to identify the level of aggremet between models results. This analysis has been incorporated into the Discussion section of the RM to enhance the interpretation of results: "Furthermore, with respect to changes in the ETCCDI indices by GCMs, it is generally observed that models projecting high negative (positive) changes in Prec also show high positive CDD (R99P) changes; while in Temp models projecting high changes also show high changes in WSDI and CSDI."

Additionally, outcomes estimated using the 20th and 80th percentiles are shown in Figures 8 and 10, while the medians of sites classified by region for each percentile are detailed in Tables 6 and 7. A description has been added to clarify the scale of these results, in the section Methods of the RM: "Emphasis was placed on exposing the percentage of change grouped by regions, as well as expressing the results obtained through boxplots to estimate the uncertainty of the GCMs using the interquartile ranges (Liu et al., 2016). Finally, the percentage of positive or negative change obtained for each hydrological condition and scenario was applied to observed series of hydro-energy parameters...".

The estimation of future projections across reference and future periods for the 20th, 50th and 80th percentiles of daily streamflow series, applied to each RoR and HPP, then we obtain their correspond hydro-energy parameters. The variations corresponding to 50th percentile are presented in Figures 9 and 11, without an areal average, whereas Figures 8 and 10, along with Tables 6 and 7, display results grouped by region using boxplots (Figures 8 and 10) and medians (Tables 6 and 7). We hope that with these comments we have answered your question.

 

Reviewer 2 Report

Comments and Suggestions for Authors

The article is very good, but some clarifications are needed that I hope the authors will consider for improvement.

A. Minor observations:
1.   The introductory paragraph correctly identifies that run-of-river hydroelectric power plants generally have a lower environmental impact compared to those with large dams. However, the greater environmental impact of dammed hydroelectric power plants is somewhat mitigated by the socio-economic importance of reservoirs. Specifically, these reservoirs associated with larger hydroelectric projects often serve multiple complex purposes, namely flood mitigation and flow regulation to ensure a reliable water supply for both the population and industry.

2. While the text points out the sensitivity of small hydropower plants to climate change, particularly concerning alterations in streamflow regimes, it's important to note that all hydropower generation is inherently vulnerable to the broader impacts of climate change on precipitation patterns and overall water availability, which are widely projected to intensify with global warming.

3.  The methodology section mentions the use of ten global climate models and three emission scenarios to assess future changes in the hydrological regime, but it is important to acknowledge that climate scenarios primarily model changes in air temperature, with subsequent, and potentially less direct, impacts on rainfall patterns and, consequently, the hydrological regime. In the absence of a detailed and exhaustive analysis of regional hydrological data and direct climate model outputs for precipitation, this inherent simplification within climate models and their application to hydrological projections should be explicitly stated. This clarification would help the reader understand the inherent uncertainties and indirect relationships involved in projecting future hydrological changes based on climate scenarios.

B. Major Observations:
1. A clear and operational definition of the different types of potential is required. Precise equations, parameters, and methodologies for calculating the gross theoretical, technical, and economic potential must be provided.
2. The hydrological model used, along with its calibration and validation process (including specific performance indicators), needs a more detailed description. For instance, an example of a flow duration curve of average daily flows should be presented, indicating the position of the installed flow and the ecological flow (which is currently undefined). The used volume on this requested graph should also be clearly shaded.
3. A preliminary economic analysis must be included. This analysis should consider capital costs, operational costs, potential revenues from energy sales, infrastructure costs, and a sensitivity analysis of key economic factors.

I trust that my observations will be considered, at least to some extent. Nevertheless, presenting the flow duration curve of the average daily flows with the mentioned parameters is essential.

Best regards,

The reviewer.

Author Response

Minor observations

Comments 1: The introductory paragraph correctly identifies that run-of-river hydroelectric power plants generally have a lower environmental impact compared to those with large dams. However, the greater environmental impact of dammed hydroelectric power plants is somewhat mitigated by the socio-economic importance of reservoirs. Specifically, these reservoirs associated with larger hydroelectric projects often serve multiple complex purposes, namely flood mitigation and flow regulation to ensure a reliable water supply for both the population and industry.

Response 1: Thanks, dear reviewer, your comment is well taken. A reference was added to point out that in large power plants part of the less favourable effects can be mitigated by the socio-economic importance of a project. In the Revised Manuscript (RM), see the introduction. "However, despite its socio-economic benefits and providing multiple services in addition to energy, such as the regulation of peak events (Kumar et al., 2021), water management, etc., it is still a very important energy source. LHP causes disturbances in ecological flow by disrupting river connectivity (Zhou et al., 2019), methane gas emissions involved in construction, and deteriorating riparian ecosystems (Campodonico et al., 2022, Auerbach et al., 2014, Poff et al., 2010)."

Comments 2: While the text points out the sensitivity of small hydropower plants to climate change, particularly concerning alterations in streamflow regimes, it's important to note that all hydropower generation is inherently vulnerable to the broader impacts of climate change on precipitation patterns and overall water availability, which are widely projected to intensify with global warming.

Response 2: Thank you for this constructive comment; we have added your suggestion. The impact of climate change on hydropower in general was specified, most strongly for SHP, and citing references were cited about the effect of changes in rainfall patterns on seasonal energy production was also emphasized. In the RM, see the introduction changes. “Therefore, it is essential to assess the impact of climate change on hydro-energy, especially in SHP, as a result of changes in precipitation and the disruption in flow regimes caused by the increased frequency of extreme hydrological events (Wei et al., 2020, Xiong et al., 2024).”

Comments 3: The methodology section mentions the use of ten global climate models and three emission scenarios to assess future changes in the hydrological regime, but it is important to acknowledge that climate scenarios primarily model changes in air temperature, with subsequent, and potentially less direct, impacts on rainfall patterns and, consequently, the hydrological regime. In the absence of a detailed and exhaustive analysis of regional hydrological data and direct climate model outputs for precipitation, this inherent simplification within climate models and their application to hydrological projections should be explicitly stated. This clarification would help the reader understand the inherent uncertainties and indirect relationships involved in projecting future hydrological changes based on climate scenarios.

Response 3: Thank you for pointing this out. The necessary changes have been implemented to add information about the BASD-CMIP6-PE product to provide details about the generation of this database and subsequently to understand the uncertainties encountered in estimating the future projection of hydro-energy potential. In the RM, see Discussion section. “Moreover, various studies evaluating the performance of GCMs in representing historical climate patterns indicate a higher accuracy in capturing temperature variations compared to precipitation; consequently, future projections of annual precipitation cycles and subsequent hydrological products, such as runoff estimates, exhibit greater uncertainty than temperature trends (Bazzanela et al., 2024, Olmo et al., 2023, Hamed et al., 2022, Lun et al., 2021, Almazroui et al., 2021). In this sense, studies focused on South America suggest that projected increases or decreases in precipitation vary significantly across models due to internal fluctuations in circulation patterns; these projections tend to show greater consistency during the mid-future period (2040–2070), whereas uncertainty increases substantially in the late future (2070–2100), where model dispersion is more pronounced (Olmo et al., 2023, Almazroui et al., 2021, Fernandez et al., 2024).”

Major observations

Comments 4: A clear and operational definition of the different types of potential is required. Precise equations, parameters, and methodologies for calculating the gross theoretical, technical, and economic potential must be provided.

Response 4: Thank you for your insightful comment. In the Historical Parameters section of the Methods, the types of capacity (potential) used in the scope of this research are described. According to Table 3, theoretical and technical capacity (CR and CT) are described with their respective equations, acronyms, and units. On the other hand, in our study we did not analyze the capacity variable, but we will include in the future a study that considers the economic approach of hydropower projects.

Comments 5: The hydrological model used, along with its calibration and validation process (including specific performance indicators), needs a more detailed description. For instance, an example of a flow duration curve of average daily flows should be presented, indicating the position of the installed flow and the ecological flow (which is currently undefined). The used volume on this requested graph should also be clearly shaded.

Response 5: Thank you in advance for your comment about the PISCO-HYD-ARNOVIC dataset; a brief description has been added. On the other hand, details about calibration, validation, and other indicators can be found in the indicated reference (Llauca et al., 2023). We have now added a supplementary Figure S02 to the detailed explanation of the daily mean flow duration curve to identify Q₈₀ and Q₉₅. Moreover, ecological flow has not been included in this study, as the scale of this study is at the regional level. In RM, the section Datasets. “... but also simulated flow series based on hydrological model ARNOVIC, considered in this study as observed streamflow (PISCO_HyD_ARNOVIC; 1981-2021); more details on calibration and validation can be found in the respective study (Llauca et al., 2023)).”

Comments 6: A preliminary economic analysis must be included. This analysis should consider capital costs, operational costs, potential revenues from energy sales, infrastructure costs, and a sensitivity analysis of key economic factors.

Response 6: Thank you for your suggestion. In this article, we have focused on identifying potential sites for the development of small-scale hydroelectric power plants at a national level, taking into account future projections of their hydro-energy parameters. However, economic analysis was not set as an objective in this study. Nonetheless, based on your suggestions, we have incorporated your comments within the discussion section as future perspectives. In the RM, section Discusions now. "The results of this study can be considered in the development of public policies for national energy planning (MINAM, 2022), aimed at closing the energy deficit gaps and quantifying the economic viability of hydro-energy projects identified at the local scale in the first instance, especially in regions that do not have access to the SEIN energy grid (Balkhair et al., 2017, Rojanamon et al., 2009).”

 

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

I thank the authors for their responses to my questions and requests.

This manuscript is valuable to the research community, and the additions have significantly improved its presentation of the research.