the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 Jun 2025
Simulating regional impacts of irrigation on the atmospheric and terrestrial water cycle using Earth System Model physics
Abstract. This study presents regional simulations over the Iberian Peninsula between 2010 and 2022 with the atmospheric (ICOLMDZ) and land surface (ORCHIDEE) components of the IPSL climate model in a new limited area model configuration (25 km resolution). It uses a recently developed river routing and irrigation scheme based on a water-conservative supply-and-demand approach. Two simulations, with and without irrigation, are compared to isolate the impacts of simulated irrigation on land surface-atmosphere interactions and the water cycle. First, an evaluation of the simulations is conducted to characterize existing model biases in river discharge, precipitation and evapotranspiration (ET), and assess whether they can be improved by simulating irrigation. The simulated irrigation is too low in southern Spain because of a lack of available water in the reservoirs, and likely because of the absence of representation of river dams. In northern regions such as the Ebro Valley, the simulated irrigation is more realistic and reduces the biases of river discharge and ET in summer and autumn. Second, atmospheric changes induced by irrigation are studied in summer (JJA). Large atmospheric responses are found over intensely irrigated areas, mainly consisting of a shift in energy partitioning between the turbulent fluxes (increase in latent heat flux and decrease in sensible heat flux, up to 50 W m⁻²), and a lowering of the atmospheric boundary layer (−100 m) and of the lifting condensation level (−250 m). Increases in precipitation are statistically significant only over the mountainous areas surrounding the Ebro Valley, and are closely linked to increases in convective available potential energy. Finally, atmospheric moisture recycling over the Iberian Peninsula is identified by showing that the increase in ET in the presence of irrigation exceeds the amount of water added by irrigation. This is made possible by an increase in precipitation over land, although most of this increase is located in lightly irrigated areas rather than in intensively irrigated areas. These results point to remote atmospheric effects of irrigation and motivate further investigation into surface-atmosphere coupling processes in the presence of irrigation in the IPSL model.
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RC1: 'Comment on egusphere-2025-2491', Anonymous Referee #1, 18 Jul 2025
Summary
Tiengou et al. used a land-atmosphere coupled model to analyze the regional impacts of irrigation on the atmospheric and terrestrial water cycle over the Iberian Peninsula. Specifically, the authors designed two simulations to simulate the climate conditions with and without irrigation, respectively. They then evaluated the irrigation volumes and terrestrial water cycle variables, and analyzed the impacts of irrigation on river discharge, precipitation, evapotranspiration (ET), and atmospheric moisture recycling. Overall, this manuscript is well-structured and the analysis is systematic. However, substantial revisions are needed before publication. The following comments are intended to help the authors improve the manuscript.
Comment
- Due to the large regional variability in climate and irrigation effects, consider explicitly naming the Iberian Peninsula in the title. Besides, the term “physics” in the current title is confusing. I suggest authors could use “Earth System Model” or “coupled land-atmosphere model” instead.
- The introduction needs updated references, especially in the first four paragraphs, which currently cite only one paper from the last five years.
- Line 33: Please update the reference from CMIP5 to CMIP6.
- Lines 48-53: This paragraph emphasizes that “irrigation can create strong spatial heterogeneities in SM”. However, the subsequent content focuses on effects of irrigation on other climatic variables rather than soil moisture (SM), which seems unrelated to aforementioned statement. The authors should clarify or connect these points.
- The authors cited so many studies regarding regional and global climatic impacts of irrigation, but didn’t clearly summarize their limitations, or explained how the authors’ study addresses them. For example, in Lines 55-68, the authors summarized that previous studies were limited to “short simulations over a limited domain”, yet this study also used only a short (13 model-year) simulation over a limited domain (Iberian Peninsula). Similarly, in Lines 70-75, global-scale studies were mentioned without clarifying their shortcomings or relevance to this study. The Introduction should be reorganized to improve logical flow and to highlight the novelty and necessity of this research.
- Line 80: The stated scientific question “which regional impacts of irrigation on surface-atmosphere couplings and the water cycle can be represented by a climate model.” does not align with the focus on that “regional climatic impacts of irrigation” indicated by the title and discussion.
- Parameter choices. The target SM is set to 60% of the SM at field capacity when calculating the moisture deficit. This proportion significantly affects the results, as different irrigation conditions could alter their climate response. Why was 60% chosen, and how would other values change the results? Besides, the assumption “Only 90 % of the volume can be withdrawn from each reservoir to maintain a minimum environmental flow” in Line 151 requires justification. The authors should perform sensitivity tests for these parameters or add uncertainty discussion.
- Line 160: When first referring to the Ebro Valley, please mark this region on Figure or a related map. In addition, basin boundaries should be included in all relevant figures.
- Line 170: It is unclear whether a 3-year spin-up (or warm-up) is sufficient for soil moisture and other variables to “reach a satisfactory equilibrium”. The authors should provide evidence to prove it.
- Section 2.3: Given that SM is a core variable for this study, the authors should validate it against observations or reanalysis data. Likewise, river discharge validation (Line 191) should be added to Table 2.
- Figure 7: Use a different color bar for variables unrelated to the water cycle (e.g., temperature), so they are clearly distinguished from the water-related variables.
- Section 3.5: Although the analysis focuses on summer, the authors should at least briefly present results for other seasons or include the relevant figures in the appendix.
Citation: https://doi.org/10.5194/egusphere-2025-2491-RC1 -
RC2: 'Comment on egusphere-2025-2491', Xabier Pedruzo Bagazgoitia, 26 Aug 2025
The present manuscript studies the regional representation of irrigation by a global Earth System Model over the Iberian peninusla regional, as well as its impact on river discharge and atmospheric variables through evapotranspiration. The authors perform two simulations: one with and one without irrigation, and analyze the difference in performance while explaining the processes behind the differences encountered. The manuscript is well structured, easy to follow and presents relevant results. I have some minor comments that could make the manuscript more consistent, and after them being addressed I would recommend it for publication.
- Some reference to the actual region studied should be mentioned in the title. Either South-Western Europe, Iberian Peninsula, or similar. Also, while I understand what is meant by ‘Earth System Model physics’, it is a bit vague of a term for the title. Please rephrase that too.
- L54: This paragraph presents the state of the art on regional modelling studies to study irrigation and atmospheric impacts. There, the LIAISE initiative, with a special focus over the Ebro basin, is mentioned but little reference is made to the studies that have been produced so far within the project. They appear vaguely in the discussion, but I believe that some of the already published studies could be present in the introduction as they shed light on the specific role of irrigation over the region of focus in this manuscript.
- L100: 2 or 3 sentences on the surface layer would help the reader to understand its basics without having to go to the references mentioned.
- L146L The calibration of routing and irrigation to from 90% to 60% of the SM at field capacity should be explained in more detail as currently there is almost no explanation of it.
- L174 I am aware this may be out of the scope of this work, but it would have been interesting to briefly look at whether there is any impact North of the Pyrenees from the irrigation south of them.
- Table 1. A validation of Soil moisture, given its critical role in evapotranspiration and the need for irrigation, would increase confidence in the simulations.
- -L245 The ‘much better match with observations’ may be for the wrong reasons. The presence of dams is used as an explanation for discharge increases in the summer that the simulation fails to catch for Figure 5e. If dams pay a role there, and acknowledging that dams may partly explain the strong overestimation of discharge in winter and spring, it is also fair to admit that over summer the irr simulations have a larger positive bias in most of the other stations than what is apparent in Fig5. In those, irr seems to agree with observations over summer but it is in fact overestimating the discharge since dams, that increased discharge at the time, are not accounted for in the simulations.
- L263. What about the role of modelled snow cover and snow melt in river discharge? There is not a single mention to this process in the whole manuscript.
- L278: Fig 6 shows a strong overestimation of precipitation over the peninsula North-West, and a strong underestimation of ET at the same time. What is the explanation for this? The validation of soil moisture mentioned before may be helpful here.
-L337: I’d still mention the underestimation (overestimation) in thalwegs (hillslopes)Citation: https://doi.org/10.5194/egusphere-2025-2491-RC2 -
RC3: 'Comment on egusphere-2025-2491', Anonymous Referee #3, 28 Aug 2025
This paper describes the implementation of an irrigation scheme in the IPSL climate model, evaluation and the impacts of its implementation on both river discharge and properties of the overlying atmosphere in regional simulations for Iberia. The manuscript is well written and quite easy to follow. I have only minor comments on the presentation.
Specific comments
L78-85: The paragraph is confusing. I wonder if in this sentence “this study aims to understand which regional impacts of irrigation on surface-atmosphere couplings and the water cycle can be represented by a climate model.” To me the impacts that are represented are the ones that are parameterised. Would it be better to say that “the study investigates the impacts of irrigation on surface-atmosphere coupling using a climate model”. But perhaps I am missing the meaning. Either way please look and revise to make the motivation and the unique selling point clear.
Fig 7: The figure would benefit from more appropriate selection of colourbars. For example, blue-red (rather than green brown) for temperature difference would be more intuitive.
L455: Missing info for Budyko 1956 reference.
Citation: https://doi.org/10.5194/egusphere-2025-2491-RC3
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