|Although the authors have tried to address the concerns that were raised during the first round of review, I am still not satisfied with the quality and the scientific contribution of this paper to warrant its publication in HESS. In a nutshell, the paper relies on a large dataset of desalination plants (DesalData) to identify grid cells that rely on desalinated water through a set of predetermined conditions (GDPC>14k, aridity<7.5%, distance<~165km) , and then through a set of assumptions, the model establishes the amount of desalinated water that would need to be produced. The established thresholds are kept the same globally and over time and as such they could yield strong implications about the future dependence on desalinated water. For example, the per capita income threshold of 14k does not account for the depreciation value of money over time, and since GDPC is expected to increase under all the 5 SSPs, this assumption will lead to wide spread of desal under all the SSP scenarios even the defragmented (and relatively poor) world of SSP3. As ground water resources start to deplete, there is no guarantee that the 165km threshold will hold and this is already seen in the case of the city of Riyadh, which is about 400km from the nearest coast. The same can be said about the aridity index threshold. Also the fact that conditions/threshold/assumptions were based on the same data that the authors are using to validate the model defeats that purpose. One would expect there is an independent dataset for calibration and another one for validation, which was not the case for this study. Even when basing the validation on the actual year (2005) to derive the grid areas depending on desalinated water and their production estimates, there are many exceptions as discussed by the authors (e.g., Spain and Israel). Finally the paper can still improve from proofreading to clarify the writing. I have tried to highlight some examples below. |
Line 18: change ‘period’ to ‘year’
Lines 25-26: I would suggest omitting the second to last sentence. If you keep it, I would reduce the number of significant figures used or use billion $ unit instead of millions (1.1-10.5 & 1.5-22.1 Billion USD). Although I am not familiar with how much desal plants typically cost, but the numbers do look small. Is it only the capital investment cost that you have accounted for? or also the levelized cost over the lifetime of the plant including operation and maintenance, and the energy cost often associated with such activities, plus piping structures, pumping and distribution costs?
Line 32: ‘there is a growing concern over the sustainability of’
Line 45: Add a more recent citation beside (Bremere et al., 2001).
Line 47: the introduction lacks any information about the current capacity & production of desal and even the historical evolution beyond citing figure S1. For example, when citing that Kim et al came up with the estimate of 250km3/yr by 2100, it is hard for the reader to give sense to how big or small that number is in comparison to current use.
Line 91: give the numbers for the rest of categories, ‘followed by brackish water, saline inland and river water, and others.’ If I am understanding this correctly, the 13.3 is the largest portion of the 21.9 total, and the other categories add up to the remaining 8.6km3, right?
Line 93: “First, we selected the desalination plants (hereafter Major Plants) to be included in our analyses.” Are not you missing the word ‘major’ in that sentence?
Lines 93-94: “The detailed selection criteria and the rationale is shown in Table S1 and Supplemental Text.” Table S1 lists the criteria but does not say anything about the rationale. For example, it is still not clear what was the rationale for using only 613 large of 17000+ plants available? The SM does not really address this point as claimed by the authors. The only piece that relates to this aspect is the following “Finally, we selected plants of larger than 10000m3d-1 of capacity. It corresponds to approximately 1.5mm yr-1 of water resources assuming the area of a grid cell is 2500km2(0.5°×0.5°), which is same order of the magnitude of other water resources components simulated in H08.”
Lines 95-96: “For example, DesalData contains some records indicating that plants in mountainous inland regions use seawater as the source, which is erroneous. The plants excluded from this study are listed in Table S2with reasons.” The mountainous example is not listed as a reason for any of the 11 excluded plants in table S2. Does that mean that criterion was never used to exclude any plant? If so, then replace with the criteria mentioned in table S2.
Lines 103-107: it is not clear yet in the flow of the paper why there is a need to collect data on the distance of desal plants and major cities. Briefly explain
Line 149: By inputting ..." rephrase the sentence. replace 'inputting' with 'using', 'extracts' with 'identifies', and 'that' with 'where'. also specify what gridded global maps are used as inputs. Also what conditions? The sentence needs to be rephrased.
Line 153: delete ‘latest’
Lines 155-157: replace “but it is not necessarily true that desalination plants are located” with ‘but desalination plants are not necessarily located’
Lines 162-164: the three conditions stand out as subjective at best. It seems that it would make more sense to discuss the data analysis first to justify the selection of these criteria
Line 167: delete “Conditions B, C, A correspond to each.”
Lines 174-176: again these seem random assumptions without sufficient justification to their logic. Where is the 30-80% coming from? The tendency to promise info to come later in the manuscript makes the manuscript harder to follow.
Line 168: “data used and spatial resolution of interest, hence modified if SDM is applied in a different simulation settings.” – not sure what this really means. Rephrase.
Line 206: replace ‘was installed’ with ‘were installed’
Line 245: “We approximated it to 30-80% and set as Assumption C.” why not use 28-77% as shown by the data?
Figure S3: Are you accounting for the diminishing purchasing power of money over time (discount rate) when accounting for the 14000$/person threshold? The SSP3 should be a ‘poor’ world with high population and difficulties to both mitigate and adapt.
Table S2: what does it mean that ‘lat/long data collapsed’? this does not make sense to me. Are you saying these points (lat/long) fall outside of the country boundary (Spain in this case)? Or something else.