the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 28 Feb 2024
The impact of future climate projections and anthropogenic activities on basin-scale groundwater availability
Abstract. Groundwater is under the pressure of changing climate and increasing anthropogenic demand. In this study, we project the effect of these two processes on the projected future groundwater status. Climate projections of Representative Concentration Pathway (RCP) 4.5 and RCP8.5 from the Coupled Model Intercomparison Project Phase 6 (CMIP6) drive a one-way coupled fully distributed hydrological and groundwater model. In addition, three plausible groundwater abstraction scenarios with diverging predictions from increasing, constant, to decreasing volumes and spatial distribution are used. Groundwater status projections are assessed for the short-term (2030), mid-term (2050), and long-term (2100) periods. We use the Bandung groundwater basin as our study case, located 120 km from the current capital city of Indonesia, Jakarta, which is currently under a relocation plan. It is selected as the future anthropogenic uncertainties in the basin, related to the projected groundwater abstraction, is in agreement with our developed scenarios. Results show that changes in the projected climate input, including intensifying rainfall and rising temperature, do not propagate notable changes in groundwater recharge. Under the current unsustainable groundwater abstraction rate, the confined piezometric heads are projected to drop up to a maximum of 7.14 m, 15.25 m, and 29.51 m in 2030, 2050, and 2100, respectively. When groundwater abstraction expands in proportion to the present population growth, the impact is worsened almost two-fold. In contrast, if the groundwater abstraction decreases because of the relocated capital city, the groundwater storage starts to show replenishment potential. As a whole, projected groundwater status changes are dominated by anthropogenic activity, and less so by changes in climatic forcing. The results of this study are expected to demonstrate and inform responsible parties in operational water management on the issue of the impact of projected climate forcing and anthropogenic activity on future groundwater status.
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RC1: 'Comment on hess-2024-26', Anonymous Referee #1, 02 Apr 2024
The paper quantifies the impact of future climate change and changes in groundwater pumping on groundwater resources in the Bandung groundwater basin, Indonesia. This is done by driving a surface water and groundwater model with CMIP6 climate projections and various groundwater abstraction scenarios. Results show that groundwater abstraction has a larger impact on groundwater levels/storage than climate-induced changes in groundwater recharge.
The paper tackles an important and relevant topic and is generally well written. The following comments identify several points that deserve attention.
-Based on the introduction, novelty of the paper seems to be largely limited to the case study, since the literature review shows that very similar methodology has been used before with similar conclusions (groundwater abstractions more important than climate change). To justify publication in HESS the authors should strengthen the novelty description of their work in the introduction. Otherwise, this paper may be better suited for a case-study oriented journal.
-One of the main conclusions is that recharge is not significantly affected by climate change. I think this result should be more extensively explained and discussed. For example, it would be useful to provide more details about how recharge is calculated. I understand the modeling has been detailed in previous papers, but the recharge calculations are central to the current paper, so they deserve special attention. This could be accompanied with more detailed results e.g. time-series of computed soil water balances and groundwater tables, to more clearly demonstrate where the increased rainfall ends up and why. This should also be accompanied by a more detailed discussion of the assumptions (are your recharge conclusions robust wrt model assumptions and chosen parameter values?). This should help clarify whether the small changes in recharge are related to the physical characteristics of the basin or to the way the model calculates recharge. Such an analysis can also increase the scientific value of the paper beyond the case study.
-I'm missing an aquifer water balance, this can be very useful to put the recharge and pumping values in perspective and to assess sustainability of the system under different scenarios.
-title: it's not the projections that will impact water availability, so better to change "future climate projections" to "future climate change" or "future groundwater recharge" (unless you actually mean that the projections will lead to decisions that will impact groundwater availability). Also, I would suggest to change "anthropogenic activities" to something more specific like "groundwater abstractions" or similar.
-line 101: to what extent is the aquitard spatially continuous?
-figure 1a: can you explain how the basin was delineated? is it based on topography?
-line 150: one-way coupling is justified if water tables are relatively far below land surface, is that the case here?
-line 168: "in each period"
-figure 2 could perhaps be simplified by only showing the workflow once but then with different climate and abstraction forcing
-line 181: the method for estimating potential ET is based on temperature and radiation and thus ignores potential changes in humidity and wind - can you justify this simplification or discuss its impact? Also, this method was apparently not developed for computing potential ET, so why is it applicable for this purpose?
-line 196: did you check that the surface shortwave radiation from MRI-ESM2-0 is consistent with that from GFDL-ESM4? Or alternatively explain why this comparison is not needed.
-line 230: are there any rain gauges in the area to check the assumption of treating CHIRPS as ground truth?
-line 250: river discharge I assume
-line 252-253: shouldn't you be using bias-corrected CMIP6 data for the historical period? Similar comment for figure 4: show the bias-corrected MRI-ESM2-0 for historical period instead of CHIRPS.
-line 274: what are the values for the storage parameters? and what are the "river-related parameters? Do the latter overlap with parameters in the wflow model?
-figure 5b: not clear what the extra horizontal lines are in this plot
-line 374: and much smaller storage coefficient in the confined aquifer?
-figure 7: make colorbar title and labels more readable
-line 416: do your simulations predict decreases in baseflow?
-line 479: what do you mean by "pseudo water table"?
-line 485: "In regions with higher margins between the groundwater recharge and soil capacity". Not clear, please clarify.
-check erroneous text on line 576
Citation: https://doi.org/10.5194/hess-2024-26-RC1 -
RC2: 'Comment on hess-2024-26', Anonymous Referee #2, 19 Apr 2024
General Comments
Dear Editors,
The manuscript deals with a very interesting theme not only for the scientific community but for the entire society, that of the comparison of the impact of projected climate forcing and anthropogenic activity on future groundwater status. I found the manuscript well written with a quite correct structure and I can say that someone can read it with pleasure. The study is quite interesting and actually, I have occupied with the same case in the past ending up with the same conclusions. For that reason, I deposit a few comments for the paper improvement.
Specific Comments
Lines 19-20: The authors indicate that there are many basins worldwide with over-exploited groundwater resources, but the references presented are only three (3). More references should be added to satisfy the word “worldwide”.
Chapter 2.1. No information is given about the water uses, the crop types, or the volumetric budget of the aquifers.
Figure 1b. The line of the cross-section AA’ should be presented in Figure 1a.
Line 109 “In recent years, the groundwater situation has not been improving” This is a very vague phrase and not properly stated. What does the word “situation” mean? I can understand very well the meaning of this sentence, but it needs to be rephrased to be more specific eg situation of what? The quantity? The quality?
Lines 238-250: I can understand that a full description of the hydrological model parameterization is reported in the previous studies (Rusli et al., 2023a, b), but a very brief report should be given here only for the most important parameters.
Lines 263-279: I can understand that a full description of the groundwater flow model parameterization is reported in the previous studies (Rusli et al., 2023a, b), but a very brief report should be given here only for the most important parameters the storage coefficient of the aquifers, the conductance of the hydraulic connection between the rives and the upper aquifer, the starting conditions, the period of simulation, the volumetric budget.
Lines 317-318: How do you explain the fact that the surface radiation reveals a tendency of a slight reduction in the future? Is this a normal, and expected result? Please justify your answer with a reference to other studies.
Figure 5.c. How do you explain the fact that the potential evapotranspiration reveals a reduction in the future, since the temperature increases? Furthermore why the potential evapotranspiration of RCP8.5 is lower than the one of the RCP4.5? Is this a normal, and expected result? Please justify your answer with a reference to other studies.
Chapter 3.3. The presentation of the results, although is very understandable and compact, is poor regarding both the size of the text and the use of the tables/graphs.
For example:
- In Lines 373-384 where the results of the the increasing groundwater abstraction scenario are presented, the results of 1) the RCP 4.5 scenario for the unconfined aquifer, 2) the RCP 8.5 scenario for both the two aquifers are missing. The phrase “Under the RCP8.5 scenario, the numbers are also concerning for the unconfined aquifers, as the groundwater table is projected to dwindle to up to 3.38 m and 3.40 m in the long run under the RCP4.5 and RCP8.5 scenarios, respectively” is not enough.
- The maps with the hydraulic head changes is a good and very useful choice but the results of the RCP 8.5 scenario and that of the other groundwater abstraction scenarios are not presented. I understand that many maps are needed for that reason, but the authors can focus on the presentation of the worst-case scenarios. There is no use in presenting the maps of Figures 7.a,b,c since the drawdown is not higher than one meter. I propose the authors find an extra way of representing the decline of the groundwater levels in relation to the time e.g. a line for each climatic and groundwater abstraction scenario (6 scenarios * 2 aquifers = 12 lines -like Fig.8) showing the decline of the groundwater level for that cell of aquifers that reveals the maximum drawdown. The same could be done for the drawdown area.
Lines 384-385: Why do you use the phrase “as expected”? It is not so obvious to the reader because the groundwater table decline was not presented in chapter 2.1. This result should be highlighted more and it should be made clear that even though the withdrawals do not increase the level will continue to fall and it should be explained why.
Citation: https://doi.org/10.5194/hess-2024-26-RC2
Data sets
Data and models used for paper 'The impact of future climate projections and anthropogenic activities on basin-scale groundwater availability' Steven Rusli, Victor Bense, Syed Mustafa, and Albrecht Weerts https://doi.org/10.4121/d9706a2a-b77b-412f-a3aa-6e22bd8ddf4a
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