Seasonal Impacts of Atmospheric Aerosols on Reference Evapotranspiration in the Mato Grosso Cerrado

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript investigates the seasonal impacts of atmospheric aerosols on reference evapotranspiration (ET) in the Mato Grosso Cerrado, with a focus on understanding the relationship between aerosol optical depth (AOD) and ET across different seasons. The study addresses a critical aspect of the water and energy balance in tropical ecosystems, and the results provide valuable insights for regional climate and agricultural water management. The methodology and data analysis appear sound, and the findings are relevant for the broader fields of atmospheric science and environmental hydrology.

 

1.      The manuscript mentions the impact of aerosols on reference evapotranspiration (ET), but there is limited discussion on how different land surface types (e.g., forests, grasslands, and croplands) may respond differently to aerosol concentrations. Given that the Cerrado region encompasses various land cover types, it would be valuable to extend the analysis to explore how vegetation type and land surface characteristics modulate the response of ET to aerosols. For example: Forests may have a different evapotranspiration pattern compared to grasslands or croplands due to differences in leaf area index (LAI), vegetation density, and stomatal conductance, which could influence their sensitivity to changes in solar radiation caused by aerosols.

2.      Another important aspect that requires further discussion is the hygroscopic nature of aerosols. Aerosols with high water uptake potential (e.g., hygroscopic aerosols such as sulfates) could significantly influence the local humidity and, in turn, the rate of evapotranspiration. This interaction is particularly relevant in regions like the Cerrado, where humidity and water vapor availability can be key factors in the ET process. The potential feedback loops between aerosol concentration, atmospheric moisture, and ET should be explored further. The paper could provide more insight into how aerosols may act not only by blocking solar radiation but also by influencing atmospheric moisture content, which could affect plant transpiration and soil evaporation.

3.      The manuscript identifies seasonal trends in the relationship between AOD and ET, but it would be beneficial to explore more deeply the mechanisms behind these seasonal variations. What are the key drivers behind the observed seasonal patterns in aerosol concentrations (e.g., agricultural activity, biomass burning)? More discussion on this would help readers understand how seasonal changes in land use or meteorological conditions contribute to the aerosol-ET relationship.

Author Response

We appreciate the comments and criticism made by the Reviewer. In the following, we provide a point-by-point response to the issues raised. The corrections in the new version are highlighted in red.

 

1. The manuscript mentions the impact of aerosols on reference evapotranspiration (ET), but there is limited discussion on how different land surface types (e.g., forests, grasslands, and croplands) may respond differently to aerosol Given that the Cerrado region encompasses various land cover types, it would be valuable to extend the analysis to explore how vegetation type and land surface characteristics modulate the response of ET to aerosols. For example: Forests may have a different evapotranspiration pattern compared to grasslands or croplands due to differences in leaf area index (LAI), vegetation density, and stomatal conductance, which could influence their sensitivity to changes in solar radiation caused by aerosols.

R/. Thank you for your comment, which highlights an important aspect of the interactions between atmospheric aerosols and land surface processes. We have addressed this concern by ex- panding the discussion on the role of land surface characteristics in modulating the ET response to aerosols. This addition has been incorporated into the manuscript (starting at line 324).

 

2. Another important aspect that requires further discussion is the hygroscopic nature of Aerosols with high water uptake potential (e.g., hygroscopic aerosols such as sulfates) could significantly influence the local humidity and, in turn, the rate of evapotranspiration. This interaction is particularly relevant in regions like the Cerrado, where humidity and water vapor availability can be key factors in the ET process. The potential feedback loops between aerosol concentration, atmospheric moisture, and ET should be explored further. The paper could provide more insight into how aerosols may act not only by blocking solar radiation but also by influencing atmospheric moisture content, which could affect plant transpiration and soil evaporation.

R/. Thank you for your comment. We agree that the hygroscopic nature of aerosols plays a crucial role in atmospheric and surface processes, particularly in biomes like the Cerrado. To address this, we have expanded the discussion to include the impact of hygroscopic aerosols on local humidity and evapotranspiration. This addition has been incorporated into the manuscript (starting at line 227).

 

3. The manuscript identifies seasonal trends in the relationship between AOD and ET, but it would be beneficial to explore more deeply the mechanisms behind these seasonal What are the key drivers behind the observed seasonal patterns in aerosol concentrations (e.g., agricultural activity, biomass burning)? More discussion on this would help readers understand how seasonal changes in land use or meteorological conditions contribute to the aerosol-ET relationship.

R/. Thank you for highlighting this important point. We agree that exploring the drivers behind the observed seasonal trends in aerosol concentrations would enhance the understanding of the seasonal variability in the AOD-ET relationship. To address this, we have expanded the discussion in the manuscript. This addition has been incorporated starting at line 349.

Reviewer 2 Report

Comments and Suggestions for Authors

The paper deals with the impacts of atmospheric aerosols on evapotranspiration. The data collected from the aerosol measuring networks are thoroughly processed statistically along with meteorological data. The conclusions are also very statistical: the revealed correlations are described in detail. However, atmospheric science (both chemistry and physics) cannot be reduced to just statistical evaluations. Besides, the use of a very complicated equation cannot replace the physical sense of a phenomenon. The authors mention the chemical composition of aerosol particles only once or twice, speaking of carbonaceous PM2.5 species. Thus, an essential portion of atmospheric aerosol  originating from the atmospheric photooxidation of vegetation-emitted organics, such as alkenes and aldehydes, is neglected. Discussing interrelations between atmospheric aerosols and air humidity, one should keep in mind the fact that the particles of atmospheric aerosol originating from different sources differ from each other in the surface characteristics: some are hydrophilic, others are initially hydrophobic. Not only the particles affect evapotranspiration, but also air humidity affects the growth of particles. This fact cannot be neglected. In the Introduction, speaking of natural and anthropogenic sources of atmospheric aerosol, the authors even do not mention vegetation as one of natural sources. The chemical composition of aerosol particles is not considered in the present paper, but it is recommended at least to mention the issues related to the aerosol formed in photonucleation of biogenic emissions. The "complex interplay" declared in lines 313-314 may just depict insufficient knowledge, why not discuss this issue even in brief? The paper would generally benefit from providing such an outlook.

Author Response

We appreciate the comments and criticism made by the Reviewer. In the following, we provide a point-by-point response to the issues raised. The corrections in the new version are highlighted in red.

 

The paper deals with the impacts of atmospheric aerosols on evapotranspiration. The data collected from the aerosol measuring networks are thoroughly processed statistically along with meteorological data. The conclusions are also very statistical: the revealed correlations are described in detail. However, atmospheric science (both chemistry and physics) cannot be reduced to just statistical evaluations. Besides, the use of a very complicated equation cannot replace the physical sense of a phenomenon. The authors mention the chemical composition of aerosol particles only once or twice, speaking of carbonaceous PM2.5 species. Thus, an essential portion of atmospheric aerosol originating from the atmospheric photooxidation of vegetation-emitted organics, such as alkenes and aldehydes, is neglected. Discussing interrelations between atmospheric aerosols and air humidity, one should keep in mind the fact that the particles of atmospheric aerosol originating from different sources differ from each other in the surface characteristics: some are hydrophilic, others are initially hydrophobic. Not only the particles affect evapotranspiration, but also air humidity affects the growth of particles. This fact cannot be neglected. In the Introduction, speaking of natural and anthropogenic sources of atmospheric aerosol, the authors even do not mention vegetation as one of natural sources. The chemical composition of aerosol particles is not considered in the present paper, but it is recommended at least to mention the issues related to the aerosol formed in photonucleation of biogenic emissions. The ”complex interplay” declared in lines 313-314 may just depict insufficient knowledge, why not discuss this issue even in brief? The paper would generally benefit from providing such an outlook.

R/. Thank you for your detailed feedback and valuable observations. We agree that incorporating a broader discussion of the physical and chemical aspects of atmospheric aerosols would significantly improve the manuscript. To address the suggested points, we have expanded the discussion in the manuscript. The texts have been added to the manuscript (starting at lines 23, 100, and 227).

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I have no more issues about this research.

Reviewer 2 Report

Comments and Suggestions for Authors

In the revised form, the paper has become much more comprehensive than in the initial version. I recommend the current version for publication.