A Risky and Potentially Costly Future: Implications of Climate-Induced Changes in Groundwater and Flooding for Coastal Dairy Farming in New Zealand
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript proposes a conceptual framework for converting slow and sudden climate risks into economic impacts in a coastal area of New Zealand. It assumes that sea level rises at the same rate as sea level rise and models severe flooding every 10 years with a cost-based model.
The manuscript presents a relevant and timely topic, but after review, some suggestions were made that could help strengthen the manuscript.
1) It is assumed that GW rise equals SLR; however, in coastal aquifers, this relationship depends on conductivity, surface and subsurface drainage, recharge, hydraulic gradients, and the presence of agricultural activities, this response may not be linear. It is suggested that the 1:1 scenario be considered central and that two sensitivity scenarios (0.5:1 or 1.5:1) be added to improve the analysis of productivity thresholds.
2) Explicitly describe that the results represent a conceptual framework and not a prediction, as well as the conditions that could generate the 1:1 scenario.
3) Modeling a severe event every 10 years to analyze the distribution of losses is not the most advisable approach; it is suggested to consider scenarios with shorter time periods, for example, 5 years, or in one case, use an annualized approach.
4) A mathematical relationship is used for ryegrass dry matter production; however, if the reader wishes to replicate the study, they must know the equation, understand the ranges of applicability, and how dry matter translates to profit. A section with the equation, units, and a more detailed explanation could be included.
5) The results show that mangrove conversion yields gross benefits compared to other options, but this may lead to double counting, additionality, and permanence for carbon credits. It is suggested that at least two cases be included: a) without monetization and b) with payments for ecosystem services.
6) Site adaptation costs should be incorporated, for example, including reconnection engineering costs or conditions for restoration to be viable, although this can be maintained conceptually.
7) The wording and consistency across sources, tables, and formulas should be reviewed.
8) Other questions also arise: What about salinization due to saltwater intrusion and its effect on pastures, soils, and water? How is the hydraulic effect on ditches and drainage modeled?
9) Can a driver system diagram be added to economic flows?
10) Incorporate an uncertainty table.
11) Is it possible to divide the results into rankings based on private market and public policy assumptions?
Author Response
Comments 1: It is assumed that GW rise equals SLR; however, in coastal aquifers, this relationship depends on conductivity, surface and subsurface drainage, recharge, hydraulic gradients, and the presence of agricultural activities, this response may not be linear. It is suggested that the 1:1 scenario be considered central and that two sensitivity scenarios (0.5:1 or 1.5:1) be added to improve the analysis of productivity thresholds.
Responses 1:
Thank you for this. We have:
- Stated that our basic assumption is for a relationship of 1:1
- Added the revised and expanded our narrative to include following caveat:
“We apply this simplified assumption for our model. Nevertheless, in practice, the relationship between groundwater rise and sea level rise will vary in response to site differences in conductivity, surface and subsurface drainage, recharge, hydraulic gradients, and the presence of agricultural activities (Ferguson & Gleeson, 2012, Michael et al., 2013, Richardson et al., 2024)
For the purpose of this exploration, we draw on work by Hamlington et al. (2024) that estimates sea-level rise in the order of 4.5 mm per year, and assume a groundwater rises the same rate (a sea level rise to groundwater rise ratio of 1:1). While the true rate of rise may be higher or lower, the logic of change remains the same. We apply a sensitivity analysis (Section 3.3) to explore implications if the rate of groundwater rise is lesser or greater than sea level rise.”
Followed your advice and provided a sensitivity analysis of groundwater rises of 1:9.5 and 1:1.5.
In the interest of accommodating the new tables, we have removed tables containing ranks (although rank data remains provided in Appendix A).
Comment 2: Explicitly describe that the results represent a conceptual framework and not a prediction, as well as the conditions that could generate the 1:1 scenario.
Response 2: Thanks for these suggestions. We have:
- Expanded the early sections to clarify the conceptual, not predictive purpose of the framework:
“Associated site adaptation options and practical solutions have been developed in consultation with local subject-matter experts (dairy consultants), drawing on their real-world, hands-on experience and the costs associated with the documentation they suggested or provided. We aim to maximise the accuracy of our representation of New Zealand dairy farming practices without exploring sensitive information, so we provide generalities for farming. Based on this, we develop a conceptual framework that integrates physical hazards and farm-level practice information with adaptation options to illustrate how the financial future may look. Recognising that this is a conceptual framework based on generalities, it is important to recognise that this framework is not yet suitable for predictive purposes as site level finances would be needed for that purpose.”
- added narratives about the 1:1 scenario in the Limitations section to make this description clear as following:
“Our exploration assumes there are no catastrophic failures in existing stopbanks and drainage systems that drastically change the viability of farming. We also assume a static ongoing sea level rise rate of 4.5 mm/year, with no future acceleration or abrupt rises (e.g. an abrupt ice shelf collapse scenario). This may not be the case given the increased rates observed over recent decades and the potential for acceleration as a result of tipping points and cascading effects not accounted for in sea level rise models (Wunderling et al., 2024). We also acknowledge that in coastal aquifers, the relationship between groundwater rise and sea level rise depends on conductivity, surface and subsurface drainage, recharge, hydraulic gradients, and the presence of agricultural activities (Ferguson & Gleeson, 2012, Richardson et al., 2024). Thus, the rate of groundwater rise may not be linear with the rate of sea level rise. The projections to 2100 should therefore be viewed as an exploration of the method and as a conceptual framework rather than a precise scenario or a prediction because the research assumes of the groundwater rise the same rate as the sea level rise.”
Comment 3: Modeling a severe event every 10 years to analyze the distribution of losses is not the most advisable approach; it is suggested to consider scenarios with shorter time periods, for example, 5 years, or in one case, use an annualized approach
Response 3: Thank you for the suggestion. With respect, we are retaining the 10-yearly flood assumption for the following reasons:
- The rationale for not annualising flood costs but specifying explicit events was to illustrate how singular events can impact profitability over time. Individual shock events provide incentives for operators to adapt (more so when several events happen within close succession). By comparison, annualising costs gives the impression of smoothness and steady, gradual declines in profitability.
As this is a conceptual framework, we see value in presenting the singular events so that people can see the impacts. However, acknowledging the value of your point, we have justified our approach by expanding the narrative as follows:
“We could apply average annual losses to illustrate the risks of flooding over time (e.g., United Nations Economic and Social Commission for Asia and the Pacific, 2019; Earthquake Commission, 2023; Federal Emergency Management Agency, Undated). However, average annual losses mask the shocks that farmers experience from individual extreme events and that provide explicit imperatives for the uptake of adaptation. Accordingly, we instead present the case where a severe flood hits the farm every 10 years to illustrate how climate change leads to spikes in costs (dips in operating profits) at the farm.”
- You have suggested we increase the frequency of our flood events to five yearly. The costs from a 10 year and a five year event are not necessarily proportional. In all likelihood, the costs of a five year event would be disproportionately lower than that of a 10 year event as stopbanks are considerably less likely to fail (although overwash from rain and the harm it causes would persist). As a result, proportionalising costs to insert five early floods is unlikely to be appropriate. Furthermore, the logic of the analysis would remain the same. Consequently, we do not believe that revising the exploration to include five-yearly floods will add significantly to the findings of the conceptual framework.
- Nevertheless, we do contextualise the frequency of flood events in NZ and how these are increasing with additional wording: “Flooding in New Zealand is a common hazard. Between 1968 and 2017 more than 80 damaging floods were reported to have occurred (Te Ara 2009). With increases in sea levels and associated rises in groundwater, the risk of storm surge and river flooding can be expected to increase (Befus et al., 2020; Bosserelle et al., 2022; Newton 2025; Nicholls et al., 1999;). The result is likely to be increases in harm from extreme events and, with increasing costs, falling profitability”
Comment 4: A mathematical relationship is used for ryegrass dry matter production; however, if the reader wishes to replicate the study, they must know the equation, understand the ranges of applicability, and how dry matter translates to profit. A section with the equation, units, and a more detailed explanation could be included.
Response 4: The report containing the formula and parameter values had been completed but had not been released online at the time of manuscript preparation. It has now released. Consequently, we have:
- Added in Appendix C reference to the detailed explanations.
- Added the link to the report in the reference for Snow et al. (2025) (https://niwa.co.nz/hazards/future-coasts-aotearoa/research-outputs/impact-rising-sea-levels-new-zealand-pasture)
- Strengthened our explanation of how declines in dry matter and feed relate to profit (volume reductions in dry matter are assumed to be replaced by purchased feed, adding the following:
“Reductions in ryegrass dry matter production are assumed to be offset by purchased feed. We assume that the greater the reduction in ryegrass production, the higher are the purchased feed requirement and the lower the operational profit. This is logical and representative of the realities in New Zealand. We use proportional declines in dry matter yield arising from waterlogging to infer potential the increases in feed costs required to maintain farm production, and the consequent reduction in operational profits that arise. Cost information on feed is adapted from Dairy NZ (2023).”
5) The results show that mangrove conversion yields gross benefits compared to other options, but this may lead to double counting, additionality, and permanence for carbon credits. It is suggested that at least two cases be included: a) without monetization and b) with payments for ecosystem services.
Response: We acknowledge that the risk exists that ecosystem service values of wetland-related options may risk double counting, additionality etc. To address this, we have:
- added the following section to the narrative:
“In representing the economic value of wetlands in this work, including values for both carbon sequestration and other ecosystem services can be precarious. It brings the risk of double counting and overstating the value that wetlands confer. To minimise this risk, we select a single other ecosystem service values whose relationship with carbon sequestration is limited – wetlands biomass as food production in supporting biodiversity ecosystem services. As some risk of overstating wetlands values may still exist, we also include a sensitivity analysis of the performance of wetland-related options (Section 3.3).”
- In relation to the question of permanence for carbon credit, added statement as following:
“However, this does not mean that mangrove related responses are necessarily practical for New Zealand. First, although saltmarshes occur in suitable habitats throughout New Zealand, mangroves only grow in the northern half of the North Island of New Zealand (Bulmer et al. 2024). Secondly, rapid mangrove expansion in many New Zealand estuaries has been driven by increased deposition of fine sediments from anthropogenic land-management practices. Thirdly, in current Emission Trading
Schemes none of mangrove or saltmarshes are included currently.”
Followed your advice and added an explicit sensitivity analysis of values with and without monetisation scenarios and tables
6) Site adaptation costs should be incorporated, for example, including reconnection engineering costs or conditions for restoration to be viable, although this can be maintained conceptually.
Response:
Our estimates of wetlands costs draw on Matthews et al. (2024) and Bulmer et al (2024). Data from Matthews et al. (2024) draws on case studies where wetlands were physically established and therefore cover all costs including engineering. The extent to which data from Bulmer et al. (2024) includes engineering costs is unclear. Accordingly, we have:
- Noted limitations to the data in the narrative.
- Added the following statement in the material and method section to make it clear:
“To determine establishment costs for salt marsh restoration, we draw on the estimates by Matthews et al. (2024 – NZD$48,000/ha) and Bulmer et al. (2024 – NZD$30,000/ha) to assume indicative establishment costs for salt marsh restoration today to be NZD $40 000/ ha (see their research for more details). In both cases, wetlands were physically established and therefore cover all costs including engineering (e.g., including reconnection engineering costs or conditions for restoration to be viable). As we used secondary data, our cost of site adaptation can be maintained as conceptual.”
7) The wording and consistency across sources, tables, and formulas should be reviewed.
Thank you for drawing our attention to this matter. We have:
- reviewed the wording and consistency across sources, tables, and formulas
- fixed the citations and checked the full name of each organizations to make sure the sources are citied correctly.
- checked numbering and presentation of tables, figures, sections and formulae to make sure the wording, statements and consistency of sections are consistent.
- In light of this, we have re-sequenced appendices and removed duplications.
Please see tracked changes throughout the manuscript.
8) Other questions also arise: What about salinization due to saltwater intrusion and its effect on pastures, soils, and water? How is the hydraulic effect on ditches and drainage modelled?
As explained in the narrative, salinisation is not included in this exploration. The implication of salinisation is that rising groundwater would eventually be accompanied by salinisation which would cause profitability to decline more rapidly. We have strengthened this observation by adding clarifying statements in the limitation section as follows:
“Due to data gaps, we do not include the impacts of climate change on salinisation of soil in this exploration. As sea level rises, it is likely that soil will be exposed to greater salinity, and ryegrass pasture production could be expected to decline more rapidly than that estimated only by reference to groundwater heights. Where sea level rise does cause soil salinisation (Water New Zealand, 2024; Parliamentary Commissioner for the Environment, 2015), profitability can be expected to decline more rapidly. The logic of our exploration remains the same at this point, but the windows for change in adaptation would contract more rapidly. In this case, farmers would likely also have incentives to explore alternative adaptation options (e.g., more salt tolerant pasture).”In relation to ditches, we note that ditches can drain excess water from soil and lower the water table but that we focus on the use of drainage ditches as a means to mitigate waterlogging from rising groundwater in this exploration.
9) Can a driver system diagram be added to economic flows?
We have added a schematic.
10) Incorporate an uncertainty table.
We have added tables for the alternative performance of adaptation options under different monetarisation/non-monetisation of ecosystem benefits assumptions and different groundwater rise rates.
11) Is it possible to divide the results into rankings based on private market and public policy assumptions?
We have:
- provided commentary in the narrative about public (ecosystem-service) values including the following:
“Based on the exploration conducted, only wetland-related options confer benefits to the public. Due to the monetised values assumed for ecosystem services of wetlands (NZD$3,076 /ha/year for saltmarsh and NZD$7,134 /ha/year for mangroves – Section 2.4.2), mangrove-related adaptation options offer the greatest benefits to the public…”
Added a table accordingly.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsI think the paper tackles a timely and underexplored issue by examining the combined economic impacts of slow- and sudden-onset climate hazards on New Zealand’s coastal dairy agriculture, with strengths in its integration of climate risk, adaptation pathways, timing, and ecosystem service valuation. However, I suggest
- I guess its contribution would be strengthened by clearer positioning within existing literature, greater transparency of the conceptual framework and assumptions, more detailed explanation of expert consultation methods and limitations, and clearer operationalisation of ecosystem service monetisation.
- I reckon the discussion of timing and long-term impacts would benefit from illustrative scenarios and a clearer distinction between exploratory and predictive claims, particularly toward 2100.
- I advise strengthening links to New Zealand policy contexts, addressing equity and distributional effects, ensuring terminological consistency, and discussing transferability would further enhance the paper’s rigour, policy relevance, and overall impact.
I suggest running a thorough English grammar and spelling check and using only one of either British or US English
Author Response
Comment 1: I guess its contribution would be strengthened by clearer positioning within existing literature, greater transparency of the conceptual framework and assumptions, more detailed explanation of expert consultation methods and limitations, and clearer operationalisation of ecosystem service monetisation
Response 1:
- Clearer positioning within existing literature:
We have added literature review on this topic of currently the literature, focusing mainly on sudden onset events, as follows:
“Examples of investigation Into sudden onset threats in New Zealand include assessments of the impact of storm surges on built assets nationally (Lan et al., 2023), analysis of associated economic risks of storm surge (Eaves et al., 2025; Nguyen et al., 2022b), the impact of permanent inundation and coastal erosion hazards (Stephens et al., 2021), impact of storm surge on stormwater and wastewater networks (Kool et al., 2020) and associated risks of storm surge and flooding on insurance retreat (Storey et al., 2024). By comparison, little has been investigated in relation to the impact of slow-onset climate change-driven hazards, such as rising groundwater. As exceptions, Setiawan et al. (2022, 2023) map salinity exposure of municipal assets and Chambers et al. (2023) model and quantify uncertainties of the temporal disposition of groundwater inundation (Chambers et al., 2023). Otherwise, most attention to slow onset hazards in New Zealand relate to adaptation and management strategies, focussing on either a specific sector of adaptation (e.g., insurance or managed retreat). Harker et al. (2016) discuss managed re-treat in New Zealand of housing and associated vulnerabilities (Harker et al., 2016). Cuendet et al. (2020) analyse adaptation options of sea level rise in Seaview Gracefield New Zealand as a case study (Cuendet et al., 2020). Mourot et al. (2022) develop a methodological framework to support adaptation (Mourot et al., 2022). Otherwise, investigation of slow onset threats has been so limited as for the UNFCCC (2012) to observe that globally even monitoring over the long term of slow-onset processes has thus far not been adequate in most countries.”
2. Greater transparency of the conceptual framework and assumptions: We have added expanded our justification of assumptions and approaches throughout the narrative, and added caveats to the Limitations and Discussion sections.
- Explanation of expert consultation methods and limitations: We have clarified our consultation process clearer as follows in the Methods section:
“Associated site adaptation options and practical solutions were developed in consultation with local subject-matter experts (dairy consultants), drawing on their real-world, hands-on experience and the costs associated with the documentation they suggested or provided. We aimed to maximize the accuracy of our representation of New Zealand dairy farming practices without exploring sensitive information. We then developed a conceptual framework that integrates physical hazards and farm-level practice information with adaptation options to illustrate what the financial future may look like. It is important to note that this work represents a conceptual framework rather than a prediction.”
- Clearer operationalisation of ecosystem service monetisation: We have clarified this in the narrative as follows:
“In our research, we included carbon credits and the ‘food provision for species’ ecosystem service as benchmarks to illustrate that mangroves and saltmarshes have monetary value. However, this approach may lead to double counting, as the same habitat is valued twice—once for carbon sequestration services and once for biodiversity-related services (i.e., food provision for species that support biodiversity). We purposely choose one conservative ecosystem service to minimize double counting …”
“… However, this does not mean that mangrove related responses are necessarily practical for New Zealand. First, although saltmarshes occur in suitable habitats throughout New Zealand, mangroves only grow in the northern half of the North Island of New Zealand (Bulmer et al. 2024). Secondly, rapid mangrove expansion in many New Zealand estuaries has been driven by increased deposition of fine sediments from anthropogenic land-management practices. Thirdly, in current Emission Trading Schemes none of mangrove or saltmarshes are included currently.”
Comment 2: I reckon the discussion of timing and long-term impacts would benefit from illustrative scenarios and a clearer distinction between exploratory and predictive claims, particularly toward 2100.
Response 2:
We have added the following statements in the discussion section:
The projections to 2100 should therefore be viewed as an exploration of the method and as a conceptual framework rather than a realistic scenario or a prediction as the research assumes of the groundwater table rise the same rate as the sea level rise.’
Comment 3: 3. I advise strengthening links to New Zealand policy contexts, addressing equity and distributional effects, ensuring terminological consistency, and discussing transferability would further enhance the paper’s rigour, policy relevance, and overall impact.
Response 3:
Thank you for this feedback. We have:
- added literature of work in assessments conducted within new Zealand and made reference to the need for further work on environmental values in New Zealand as well as the relevance of our work to the emissions trade scheme (and possible variation).
- added commentary and values for public (ecosystem-service) benefits, noting that only wetland-related adaptation options confer public benefits
checked the manuscript for sources, citations, terminologies and cross references. Our changes are tracked throughout the manuscript.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for Authors The authors have made improvements to the manuscript. These improvements help to better explain the methodology and some key concepts. The manuscript is more robust in its current state and can be published.