the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 Jun 2025
Enhanced Vegetation Evapotranspiration Increases Precipitation in Oasis Regions
Abstract. While the impact of vegetation on global climate has been confirmed, the feedback mechanisms between vegetation and precipitation at local scales remain unknown. This study selects oasis as relatively independent geographical units and analyzes stable isotopes in precipitation, soil water, and xylem water across four different vegetation cover areas. Results show that in oasis areas, tree-covered regions have the highest recycled vapor ratio (fre), averaging 53 %, and the lowest raindrop re-evaporation rate (fre-ev) at 38 %. Cropland, grassland, and shrub-covered areas have lower fre (39 %) and higher average fre-ev (between 60–70 %). In comparison, desert areas show more extreme differences between these two vapor ratios, further indicating that vegetation transpiration can increase precipitation by inhibiting sub-cloud re-evaporation loss of raindrops. This provides new insights into the impact of local vegetation on precipitation changes. In future assessments of water resources in arid environments, the effects of vegetation transpiration, recycled vapor, and secondary evaporation of precipitation on local water resources cannot be ignored.
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CC1: 'Comment on egusphere-2025-2410', Nima Zafarmomen, 06 Jul 2025
Overall the paper makes a valuable contribution to the field.
- Limited Clarity in Experimental Design Description: The experimental analysis section (3.2) describes the process of sample collection and isotope analysis but lacks detail on critical aspects, such as the number of replicates, sampling frequency, or specific environmental conditions at the collection sites. This omission makes it difficult to assess the robustness of the methodology. The authors should provide a more comprehensive description of the experimental setup, including site characteristics, sampling protocols, and potential sources of variability, to strengthen the reproducibility of the study.
- Incomplete Data Presentation in Table 1: The document repeatedly references Table 1 for stable isotope variations in precipitation, soil water, and xylem water (Page 7), but the actual table is not included in the provided excerpt. This absence hinders the ability to evaluate the reported isotope values (e.g., average δH of -35.19‰ for forest precipitation). The authors should ensure all referenced tables and figures are included and clearly labeled, with sufficient explanation of the data to support their interpretations.
- Ambiguity in Model Application and Assumptions: The use of the Craig and Gordon model and the Keeling plot equation (Section 3.3.1) is appropriate for isotope-based evapotranspiration partitioning, but the manuscript does not adequately justify key assumptions, such as the equivalence of oxygen isotope composition in vegetation transpiration and xylem water (δI = δET). This assumption may oversimplify complex physiological processes. The authors should provide supporting references or empirical evidence for such assumptions and discuss potential limitations to enhance the rigor of the analysis.
- To strengthen the literature review and demonstrate relevance to hydrologic modeling: Please consider citing studies such as: "Assimilation of Sentinel-Based Leaf Area Index for Modeling Surface–Groundwater Interactions in Irrigation Districts" which shows the role of vegetation dynamics in altering atmospheric and subsurface water interactions.
- Lack of Quantitative Data for Key Claims in Discussion: The discussion section (Page 14) makes bold claims about the contribution of crop transpiration (62%) and recycled water vapor from trees (53%) to atmospheric water content, but these figures lack context regarding statistical significance, error margins, or comparisons with other studies. Without this, the claims appear speculative. The authors should include quantitative measures of uncertainty (e.g., standard errors) and compare their findings with existing literature to substantiate their conclusions and improve the scientific impact of the study.
Citation: https://doi.org/10.5194/egusphere-2025-2410-CC1 -
RC1: 'Comment on egusphere-2025-2410', Anonymous Referee #1, 29 Jul 2025
This manuscript presents potentially interesting and important analyses of stable isotopes in precipitation, soil water, and xylem water in oases, which may yield new insights in local moisture recycling in these areas. However, unfortunately, the quality of the manuscript is below par.
The manuscript is very weakly written. The structure is unclear and the English is poor. This results in sometimes incorrect statements, which is a major concern. Examples include calling plants “buffer zone” or stating that the growth of vegetation results from “the synergistic stimulation from increased water and nutrient supply under global warming.”
The introduction of the research aim is too weak. Apparently the authors aim at “solving the problem of precipitation distribution patterns”, but what problem this is exactly is unclear. The isotopes appear out of nowhere, and introduction section does not include any introduction of the study area, leaving the reader guessing what is meant by “the oasis” or “the region”. This is illustrative of the unjustifiably generic claims that the manuscript makes, leading to overpromises of the results. It is sometimes hard to judge the merits of the work, because of blurriness between findings and interpretations (example: lines 169-172), but surely generic claims such as in the title and abstract, but also in the following sentences, are not justified:
“The research results will help fully elucidate the impact of vegetation evapotranspiration on precipitation and consider the regulatory effect of vegetation on precipitation and atmospheric water vapor from the perspective of heat transfer.”
“This study, using stable isotope analysis, found that the water consumption capacity of crop transpiration far exceeds soil evaporation.”
Beyond the quality of writing, sloppy mistakes in the text and figures make it difficult to trust the carefulness of the work. The authors need to carefully consider what to show and how, and take the reader along in the message, which is not the case now. For example, three new figures are presented in the Discussion, including a “calibration of different models” as the final figure. Section 5 is headed “4: Discussion”, but also section 6 is headed “Discussion”.
Citation: https://doi.org/10.5194/egusphere-2025-2410-RC1 -
RC2: 'Comment on egusphere-2025-2410', Anonymous Referee #2, 10 Sep 2025
General Comments:
I commend the authors for their considerable efforts in obtaining long-term, continuous observational data. Such in situ measurements from an oasis-desert ecosystem are highly valuable and provide a robust foundation for directly investigating vegetation-precipitation responses.
The study's objective—to elucidate the feedback mechanisms by which oasis vegetation influences local climate, particularly through transpiration-induced precipitation—is both timely and significant. The potential implications for ecosystem restoration and water resources management in arid regions are considerable.
However, the manuscript in its current form requires major revision to meet the publication standards of HESS. The central conclusion regarding plant transpiration increasing precipitation requires more rigorous substantiation. The logical relationships and computational methodologies underpinning this conclusion must be carefully scrutinized and strengthened. Furthermore, a critical oversight is the lack of discussion regarding the role of groundwater irrigation in sustaining the oasis ecosystem, which is fundamental to the hydrological cycle described.
While the overall narrative is readable, the logical framework requires consolidation, and the results section presents findings that are currently vague and require clearer articulation. I strongly recommend a thorough revision of the language to eliminate ambiguity, particularly in key sentences conveying the core findings. I encourage the authors to address all points raised below proactively.
Major Comments:
Abstract:
The abstract does not clearly articulate the inhibitory relationship between recycled water vapor (fre) and re-evaporation vapor (fre-ev). The findings of Jiao et al. should be contextualized: in regions with high recycled vapor, sub-cloud secondary evaporation loss is minimal. The vegetation-precipitation response narrative should also integrate key meteorological variables such as near-surface air temperature and relative humidity.
The concluding statement on water resource assessments should be reframed to focus on the study's specific implications. Replace the current sentence with: "This finding also implies that the potential impacts of large-scale ecosystem restoration in arid regions on water resource availability must be re-examined."
Introduction:
The introduction requires significant improvement in logical coherence, readability, and reference accuracy.
Logical Reorganization: The flow of argumentation should be restructured as follows:
- a) Global context and research motivation.
- b) The process mechanisms (e.g., ET → moisture budget → boundary layer/LCL → sub-cloud re-evaporation → precipitation) that form the basis of the scientific questions.
- c) Identification of the research gap and a clear statement of the research hypotheses.
- d) Justification of the study area's typicality and particularity.
- e) Clear articulation of the research objectives and significance.
Explicit Hypotheses: The following two hypotheses need to be explicitly stated:
- a) Different vegetation types alter the proportion of recycled water vapor by modifying evapotranspiration (ET) fluxes and the partitioning of its components.
- b) Vegetation-induced changes in the near-surface thermodynamic state (temperature and humidity) modulate the lifting condensation level (LCL) and raindrop re-evaporation rate, creating a feedback loop to precipitation intensity and isotopic signatures.
Reference Accuracy: Correct “De et al., 2013” to “De Frenne et al., 2013”.
Focus: The second paragraph is tangential to the paper's focus on hydrological processes. Its content should be refined to progressively narrow the scope toward water-vapor feedback processes.
Study Area:
Clarify whether the value of 2580.7 mm refers to actual evapotranspiration or potential evapotranspiration.
Materials and Methods:
Sampling Details: The sampling methodology is insufficiently detailed. Please provide specific geographic coordinates of the sampling sites, the number of samples collected, and the plant species sampled.
Equation Notation: Carefully check the consistency of all subscripts and symbols in the equations, both in the main text and in the Supporting Information. Ensure all equations are appropriately referenced.
Supporting Information: Place the citation for Table S1 in a more prominent location within the methodology section.
Discussion:
Critical Pathway: The proposed sequence of “enhanced transpiration → suppressed sub-cloud re-evaporation → increased precipitation” relies on the intermediary pathway of “near-surface humidity and temperature → LCL → raindrop re-evaporation rate.” I recommend strengthening this argument by establishing clear statistical associations between observational/reanalysis data for relative humidity (RH), LCL, and fre-ev>.
Impact of Irrigation: For oasis croplands, agricultural irrigation is the primary water source. The authors must explicitly address how irrigation water, as distinct from natural precipitation, influences the calculated cropland evapotranspiration fluxes and the subsequent interpretation of the local water vapor recycling.
Minor Comments:
L11: Revise “four different vegetation cover areas” to “four vegetation cover types”.
L14: Express the range as “60–70%” (using an en-dash).
L15: Revise to: “…further suggesting that enhanced vegetation transpiration may increase precipitation by reducing below-cloud re-evaporation losses.”
L26: The citation should be: (Huang et al., 2023).
L38: Revise to: “As a relatively humid enclave at the desert margin…” to avoid mischaracterizing an oasis as a broadly humid region.
L67: Please verify the figure citation; it is likely intended to be (Fig. 1).
L71: Cite the dataset mentioned in the Acknowledgements here: “Daily precipitation and evaporation data were provided by the National Ecosystem Science Data Center, National Science & Technology Infrastructure of China.”
L117: Discuss the potential uncertainty introduced by using surface atmospheric pressure as a proxy for water vapor in the calculation of the F value.
L128 & L133: Ensure consistency between in-text citations and the reference list. The main text cites "Pruppacher and Klett, 2010" and "Rogers and Yau, 1989," but these must match the entries in the References section.
L223: Correct the numbering to “5 Discussion”.
L273: Correct the subheading to “6 Conclusion”.
Table 1: Please add a footnote explaining the meaning of the “/” symbol.
Figure 1: The caption should clearly differentiate the panels: “(a) represents the sampling point..., (b) represents..., (c) represents...”
Figures 2 & 4: Perform statistical significance tests on the data presented and indicate the corresponding p-values directly on the figures. In Figure 4, ensure the colors representing different rainfall intensities are consistent across panels (b), (c), and (d).
Figure 7: In the caption, clarify panel (b) by stating: “Initial raindrop diameter back-calculated from the microphysical end-state based on the re-evaporation model…” to avoid confusion with panel (a).
Citation: https://doi.org/10.5194/egusphere-2025-2410-RC2
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