In this article, the authors explore representations of evapotranspiration in the chemistry-climate model EMAC, and how this impacts air temperature as well as air pollution, focusing mainly on tropospheric O3. The remarks below need to be addressed before the manuscript can be accepted for publication.   

This work presented is within the scope of the journal, and I think the results are robust and quite interesting. However, I have two major concerns:

1. I think the manuscript has a lot of build-up but then the implications on air quality are not discussed thoroughly. In other words, Section 3.5 needs to be expanded. I listed some suggestions below. 
2. I had to re-read some text multiple times to understand what the authors wanted to say. I strongly recommend the re-writing of some parts. It would probably be a good idea to send the manuscript for proofreading. 

General comments:

While reading the manuscript I came across words written in US English and British English. Please be consistent.

I think the manuscript would benefit from having an “Experimental design” section where you describe the experiment setup in detail. i.e., not just the relevant parameterisations, but also the submodules responsible for the land surface, vegetation, etc.

It is not clear what vegetation representation is being used. It was only later in L357/358 that I realised that you have no vegetation in your model. This should be made more clear. The suggestion above would help to clarify this. 

Figure captions are way too short. Generally one should be able to understand the figure completely from the caption without referring to the main text (i.e. self-describing). E.g., Fig. 2 - “Anual mean maximum assimilation” Assimilation of what?

Fig. 3 was not discussed enough in the text. Please update the figure’s caption (see above), and also provide the geographical extent of the areas considered.

I find some of your colour bars confusing. When using a diverging colour bar, please decide whether you want the min/max to be pointy or not, but be consistent! The min/max of the colour bars is misused in most of the figures presented.

Fig. 4 - Fix the colour bar for subplot (a). Caption - Which panels are from EMAC and which are not?

Fig. 8 - Color bars. Why do you have a change in stomatal conductance over deserted regions, e.g., the Sahara desert? Please explain this, and if the values are negligible consider applying a mask.

Section 3.5: In the supplement, you show a strong decrease in isoprene mixing ratios. Could you also show the absolute difference not just the relative (%) change?

From Fig. 6 I would expect a strong increase in isoprene emissions given the increase in surface temperatures. Would be nice to dig in deeper here and quantify the increase in surface isoprene emissions and see how this increase compares to the decrease in isoprene concentrations from enhanced OH oxidation. Also, provide details on the isoprene emissions and sensitivities. Are you using MEGAN? 

Fig. S1: In some places over Africa (e.g. 20-30 deg S), you show a decrease in the OH radicals but this does not correspond to an increase in isoprene. Why is that? This seems to violate your hypothesis that isoprene concentrations go lower because of increased loss by OH. Similarly, could you explain the hotspot (increase in isoprene) over Antarctica where there are no apparent corresponding changes in OH?

Please include some limitations in your study. E.g. No vegetation representation, and the fact that the biosphere and BVOC emissions do not respond to changes in tropospheric chemistry e.g. ozone concentrations.

Specific comments:

L26: When writing “e.g.” for citations, it is generally expected that you mention more than one study. Please correct all other instances in the manuscript. 

L29: ”(plant’s pores)” - I don’t think this is needed here. 

L36/37: “Currently” should go at the start of the sentence.

L51: “non-stomatal processes in plants”  - like what?

L61: “GLEAM” - Is this an acronym? Please define acronyms on their first instance.

L61: More details are needed on the EUMETSAT satellite you are referring to. 

L90: Include unit for LAI m2/m2.

L98: Latter not “later”

164: EUMETSAT was already used. Please define in the first instance.

L184/85: Not clear what you mean here. Do you mean the sum of the bare soil, short/tall vegetation evapotranspiration per grid box?

L193: mmday-1 - why italic?

L246/253: Text not clear. Please consider rewriting this part. “Saharian” - do you mean Sahara desert? 

L250: The distribution of transpiration inf Fig. 2b follows patterns of vegetation distribution e.g. LAI. Why would the additional soil moisture in the tropics explain the geographical distribution?

L302: “African desert” - Sahara desert

L308: “...in the southern part of South America …..”

L344: “to to”

L352: “... respective changes in tropospheric ozone….”

L392/393: Provide more details on the “bucket model” in EMAC or JSBACH.

L394: JSBACH - define the model acronym.

L405: “...(LSMs) generally agree with…”

L414: Double brackets.

L401/402: Give more details on the ‘ozone-climate penalty’. What is the benefit suggested in Zanis et al. 2022?

Emmerichs et al. assessed the implementation of various functions related to plant water stress in the ECHAM/MESSy model and examined their subsequent effects on change in evapotranspiration. The authors also investigated the impact of changes in evapotranspiration on ground-level ozone. While this modelling exercise is valuable for pinpointing the appropriate functions implemented in their atmospheric chemistry model, there are a few drawbacks in the current form of this paper, particularly regarding the overall structure and model-data validation. Here I provide some comments for the authors’ and editor’s consideration.

Major comments:

1. The title of this paper is misleading. It led me, as a reader, to expect a primary focus on how plant-water stress influences ground-level ozone. However, two-thirds of the Results are on testing/comparing the impact of changes in plant-water stress functions on plant transpiration, evapotranspiration, and air temperature. Ozone is only a minor aspect of the findings. It might be more appropriate to adjust the title to better reflect the actual results. If the authors aim to quantify the effect of plant water stress on ozone, the results should provide the correlation between the water stress index/ET/Temperature and ozone concentration.
2. It is not clear to me from the text how the change in evapotranspiration (ET) will affect ozone concentration through atmospheric chemical processes. I was trying to get some basics from the Introduction and Method but was unsuccessful. Although the author does mention chemical processes in Section 3.5, it would be more effective to introduce this information much earlier to provide a general understanding of how changes in ET could impact ozone. While the relationship may be self-evident in atmospheric chemistry, it is still essential to include basic information in the paper to present a comprehensive story.
3. A major concern regarding the model's performance is the absence of model-measurement validation. All data presented in Section 2.2 consist of simulations from other models. No ground-based data were used to validate the ET estimates obtained by modifying the plant-water stress functions in their model. Data from EMUETSAT or GLEAM may provide a robust estimation of ET by validating their performance against ground-based measurements. As an independent model, the outputs from ECHAM/MESSy should also be validated against ground-based measurements. It is feasible to get the ET measurements from the FLUXNET network nowadays. A direct comparison in a 1:1 space, plotting ground-based measurements against model estimates, would provide a clear assessment of the model's performance and illustrate how changes in plant water stress functions impact ET and other model outputs.

Minor comments:

1. The first 4 sentences of the abstract were written in a way that jumps from one topic to another without logical connections.
2. “Overall, the new functionalities” What do these new functionalities refer to? No mention in the previous text.
3. Before Line 55, there should be a section to introduce the research background on ozone using modelling.
4. In line 55, please provide the full name of MESSy, where it is first introduced.
5. From Lines 105 to 115, it is not clear what are inputs and outputs from the listed equation. It states (L154) that “The two schemes are combined afterwards to yield a smooth function for An” and then (L108)“ to yield the stomatal conductance (gs)”. Is An used to calculate gs after An is derived from Am?
6. The temperature dependence of gm is highly variable. What function is used to describe gm and why in your model?
7. Line 119 how do you implement the water stress function into the stomatal conductance? Please provide the used function here.
8. Figure 2 How the Am,max is derived? It seems unrealistic in central Australia and southern Africa where most of the area is desert with low photosynthesis but model predictions of Am,max are high in those regions in panel a.
9. Line 344, delete “to”
10. Line 372 Please elaborate on the correlation between stomatal conductance and photosynthesis and how the change in CO2 concentration will affect the stomatal conductance and photosynthesis differently.