the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 May 2024
Long-term Hydro-economic Analysis Tool for Evaluating Global Groundwater Cost and Supply: Superwell v1.0
Abstract. Groundwater plays a key role in meeting water demands, supplying over 40 % of irrigation water globally, with this role likely to grow as water demands and surface water variability increase. A better understanding of the future role of groundwater in meeting sectoral demands requires an integrated hydro-economic evaluation of its cost and availability. Yet substantial gaps remain in our knowledge and modeling capabilities related to groundwater availability, feasible locations for extraction, extractable volumes, and associated extraction costs, which are essential for large-scale analyses of integrated human-water systems scenarios, particularly at the global scale. To address these needs, we developed Superwell, a physics-based groundwater extraction and cost accounting model that operates at 0.5° (≈50x50 km) gridded spatial resolution with global coverage. The model produces location-specific groundwater supply-cost curves that provide the levelized cost to access different quantities of available groundwater. The inputs to Superwell include recent high-resolution hydrogeologic datasets of permeability, porosity, aquifer thickness, depth to water table, and hydrogeological complexity zones. It also accounts for well capital and maintenance costs, and the energy costs required to lift water to the surface. The model employs a Theis-based scheme coupled with an amortization-based cost accounting formulation to simulate groundwater extraction and quantify the cost of groundwater pumping. The result is a spatiotemporally flexible, physically-realistic, economics-based model that produces groundwater supply-cost curves. We show examples of these supply-cost curves and the insights that can be derived from them across a set of scenarios designed to explore model outcomes. The supply-cost curves produced by the model show that most nonrenewable groundwater in storage globally is extractable at costs lower than 0.23 USD/m3, while half of the volume remains extractable at under 0.138 USD/m3. We also demonstrate and discuss examples of how these cost curves could be used by linking Superwell’s outputs with other models to explore coupled human-environmental systems challenges, such as water resources planning and management, or broader analyses of multi-sectoral feedbacks.
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Status: open (until 24 Jul 2024)
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RC1: 'Comment on egusphere-2024-799', Anonymous Referee #1, 10 Jun 2024
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This manuscript outlines the development of a tool that can estimate the cost of groundwater pumping across the globe. The cost and availability of groundwater pumping is a timely and important area of research, particularly in the context of climate change and increased pressures on our water supplies. My expertise is in hydrogeology and water management, and as such I will be primarily commenting on those aspects.
This manuscript is very well written and brings aspects of hydrogeology and economics together in a clear manner. I do have several concerns with respect to the methodology, particularly the explanation and description of the drawdown assessments, and with the exclusion of any other aspect of the hydrologic cycle within the analysis.
- I don’t feel that this tool evaluates groundwater supply, as described by the title and implemented in the research. It seems to provide one static quantification of availability but doesn’t include any other aspect of the hydrologic cycle that effects the ever evolving groundwater volumes and availability across the globe. I think you could argue that this tool can evaluate changes in supply due to pumping, but the lack of connection with any other part of the hydrologic cycle makes the claim of evaluating groundwater supply very thin.
- Recharge needs to be mentioned WAY before the very end. There are various sources of estimated recharge rates across the globe. I understand that it would bring in a lot of uncertainty, but this is already wrought with uncertainty, I’m not sure how much it would change it. This is connected back to the exclusion of any other part of the hydrologic cycle.
- Lateral inflows are inherently part of Theis – it is assumed that there are infinite sources of water available laterally. Saying you aren’t including them is erroneous unless you have modified Theis to include boundary conditions of some sort.
- If the wells are pumped for 100 days (which may be very short for many parts of the globe), are they in recovery for the remaining part of the year? Is that simulated or do you just pause the groundwater levels after 100 days and start from there the next year? Both have obvious assumptions and limitations but it is not clear from the manuscript which approach is taken. I would hope that recovery is enabled through inclusion of modified Theis.
- Some discussion of the uncertainty in all of the datasets you use as inputs would be beneficial. Particularly because they are dependent on data that is now over a decade old. For example, how does Fan et al. (2013) capture different aquifer units? There are many instances where irrigators use deeper aquifer units that are overlain by shallow, unconfined units. In addition, how does Gleeson et al. (2014) capture this same issue? What about fractured rock aquifer which are prolific in many parts of the work and are very productive.
As a result of the concerns above, in addition to some more specific, yet related comments provided below, I suggest this manuscript be returned for major revisions.
Specific Comments
- Figure 3: Do you check to see if the well interference and Jacob correction result in a violation?
- Line 220: The accepted definition of saturated thickness is the depth from water table to a bottom confining unit, not to the depth of the well. The well can draw water from below as it follows pressure gradients. It is fine to keep this definition, but I would be clear that you are defining it much differently than the convention.
- Line 241-244: You are assuming that there are always adjacent wells? Or do you do this when the number of wells in the grid meet a certain criteria?
- Line 252-254: You should provide the main categories of aquifers that you use – I presume they are unconfined and confined? The reader should be provided this information without having to look through supplemental information. I would guess this category determines whether the correction is needed.
- Line 264: Here you mention an ‘off period’ – is this simulated as recovery (as per comment above)?
- Line 362: Some context for these two depths would strengthen this work – do they correlate with particular crops?
- Line 373-375: Some regions of the Ogallala are already well beyond these value, some having already depleted most of their resources. This treatment of the aquifer as one large unit is inconsistent with how it actually works. To account for this, just reword to say that on average, it was 30% depleted – if you want upper and lower bounds you can look at recent Kansas Geological Survey reports to see the ranges within Kansas – this would communicate to the reader that you understand that these units do not operate as one big bathtub.
- Section 3.2.1: I struggle with this whole section because nothing here is new or novel to the hydrogeology community. I understand that this manuscript is reaching a multidisciplinary audience but given the length of the manuscript I think it could be moved to supplemental information.
- Line 453: How does the Vavailable term change with time? Again, the problem with this is that you are completely removing GW from the hydrologic cycle. There is data and research that can support bringing it back in (e.g. inclusion of recharge), and I don’t feel that doing so is an unreasonable request.
- Figure 5: When is this representative of? Groundwater supply is not stationary and constant. Also interesting that the Great Lakes are not removed from this reporting, as with other inland lake regions - was there a reason for this?
- Section 6.1: Since you highlight the ability to work at a variety of scales (Figure 11), I would think that the first step could be to calibrate against smaller-scale depletion – for example the well documented depletion in the High Plains Aquifer that you discussed earlier.
- Section 6.3: As described in several previous comments, I think this is a bigger issue than this one paragraph insinuates. I don’t have additional comments beyond those given in sections above, but rather point to this as one place that can be extended to better capture the implications of the rest of the hydrologic cycle on this work.
Citation: https://doi.org/10.5194/egusphere-2024-799-RC1
Data sets
Global Geo-processed Data of Aquifer Properties by 0.5° Grid, Country and Water Basins H. Niazi et al. https://doi.org/10.57931/2307831
Globally Gridded Groundwater Extraction Volumes and Costs under Six Depletion and Ponded Depth Targets H. Niazi et al. https://doi.org/10.57931/2307832
Model code and software
superwell: v1.0 H. Niazi et al. https://doi.org/10.5281/zenodo.10828260
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