The Role of Vegetation on Urban Atmosphere of Three European Cities—Part 1: Evaluation of Vegetation Impact on Meteorological Conditions

Round 1

Reviewer 1 Report

A very good manuscript, well set out and explained, good figures and detailed results

Author Response

We would like to thank the reviewers for their useful and constructive suggestions that helped us improving the quality of the paper. We address below each specific issue raised by reviewers (blue text) updating the manuscript accordingly.

 Reviewer#1: We thank very much the reviewer for reading our manuscript and appreciating our work.

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear author, your paper "The role of vegetation on urban atmosphere of three European cities. Part 1: Evaluation of vegetation impact on meteorological conditions" deals on the modification of some monitorizable climate characteristics such as wind due to the presence of vegetation (trees, srubs...) in major cities.

Please consider my comments as suggestions in order to improve the quality of your manuscript.

Line 53 illnesses instead of illness.

Line 60-62: is it possible to add the regulatory text that stimulates your research? i.e.:

To face these effects and their worsening trend in a climate changing environment, it is crucial for local communities and governments to evaluate, plan and implement mitigation measures, especially in urban areas. To do so, the European Union approved a regulatory package, being one of their exponents the Directive 2008/50/EC of the European Parliament and of the Council of 21 May 2008 on ambient air quality and cleaner air for Europe (AAQ Directive).

Please consider this comment also for the Part 2 research manuscript.

Material and Methods: please indicate and explain what informatic programmes were used to perform the models and present your results (figures).

Line 227: discussion instead of discussions.

Line 242: In figures 3 and 4 instead of "In these figures".

Figure 2: please add the north arrow (see figures 3 and 4) and, if possible, increase the size of axes labels. 

Figures 3 and 4: please increase slightly the width of the municipality boundary area (see figure 2).

There are not serious flags on the Quality of English.

Author Response

Responses to Reviewers

We would like to thank the reviewers for their useful and constructive suggestions that helped us improving the quality of the paper. We address below each specific issue raised by reviewers (blue text) updating the manuscript accordingly.

Reviewer#2: Dear author, your paper "The role of vegetation on urban atmosphere of three European cities. Part 1: Evaluation of vegetation impact on meteorological conditions" deals on the modification of some monitorizable climate characteristics such as wind due to the presence of vegetation (trees, srubs...) in major cities.

Please consider my comments as suggestions in order to improve the quality of your manuscript.

• Line 53 illnesses instead of illness.

 Done, thank you.

• Line 60-62: is it possible to add the regulatory text that stimulates your research? i.e.:

To face these effects and their worsening trend in a climate changing environment, it is crucial for local communities and governments to evaluate, plan and implement mitigation measures, especially in urban areas. To do so, the European Union approved a regulatory package, being one of their exponents the Directive 2008/50/EC of the European Parliament and of the Council of 21 May 2008 on ambient air quality and cleaner air for Europe (AAQ Directive).

Thank you for the suggestion. Additional text has been added to manuscript at lines 83-89.

• Please consider this comment also for the Part 2 research manuscript.

Material and Methods: please indicate and explain what informatic programmes were used to perform the models and present your results (figures).

Thank you for the suggestions. Besides the references to the WRF model and its applications, we added some explanatory text in Section 2. Moreover, a mention to the software used for analysis and plots is added at the end of subsection 2.3.

• Line 227: discussion instead of discussions

 Done. Thank you.

• Line 242: In figures 3 and 4 instead of "In these figures"

 Done. Thank you.

• Figure 2: please add the north arrow (see figures 3 and 4) and, if possible, increase the size of axes labels. 

Figure 2 was modified accordingly. It is clearer now. Thank you.

• Figures 3 and 4: please increase slightly the width of the municipality boundary area (see figure 2).

We improved the quality of Figures 3 and 4 increasing the municipality borders line width. Thank you for the warning. 

Author Response File: Author Response.pdf

Reviewer 3 Report

The data presented in this research show the effect of vegetation on urban meteorological conditions. Interesting findings from the research have been found, yet there are several queries and criticisms about the publication that need an explanation.

Why did the authors decide to focus on these three cities (Milan, Bologna, and Madrid)? The authors made no attempt to defend their choice.

Calculations were based on climatic data from 2015. However, such extreme years are very rarely repeated. How closely does vegetation's impact on meteorological indicators in a "extreme climate year" compare to its impact on an "average climate year"?

The data in subsection 2.2.2 does not specify which urban vegetation was taken for analysis. The first thing we want to know is how much total green space there is in each of these cities and what percentage of that total city area is made up of green space. What tree and shrub species are prevalent in a certain city. How fragmented the greenery is. What primary forms of vegetation are represented by green areas (forests, artificial stands, parks, squares, and shrubs)? All these green space criteria determine how much they can affect climatic factors.

Numerous water bodies (rivers, canals, lakes, and ponds) may be found in these cities. For instance, consider the rivers Manzanares, Reno, Savena, and others, which have woody vegetation growing on their banks (as a component of the city's green areas). Due to their cooling effect throughout summer, water bodies have a considerable impact on microclimatic indicators. Did the authors consider this fact in their calculations? How were the impacts of water bodies and vegetation on changes in meteorological indicators divided?

The calculations were performed using grid cells with a size of 1 km by 1 km. How logical is the selection of such a big grid cell size? Do the authors think that vegetation impacts meteorological indicators over such a wide range (i.e., up to 1 km from green areas)?

Technical issue

Please use the same terminology throughout the text. Simply use Milan or Milano as the city name.

Author Response

Responses to Reviewers

We would like to thank the reviewers for their useful and constructive suggestions that helped us improving the quality of the paper. We address below each specific issue raised by reviewers (blue text) updating the manuscript accordingly.

Reviewer#3: The data presented in this research show the effect of vegetation on urban meteorological conditions. Interesting findings from the research have been found, yet there are several queries and criticisms about the publication that need an explanation.

• Why did the authors decide to focus on these three cities (Milan, Bologna, and Madrid)? The authors made no attempt to defend their choice.

Thank you very much for your question. As we stated in the introduction, this work reflects the outcomes of the EU-LIFE project VEGGAP and the cities and are representative of small, medium and large size European ones. We added some text in the manuscript (line 80) to better clarify that. As we found, and mentioned in the conclusions, the strong dependence of meteorology on vegetation and on city’s peculiarities emphasises the importance of further similar studies in other cities.

• Calculations were based on climatic data from 2015. However, such extreme years are very rarely repeated. How closely does vegetation's impact on meteorological indicators in a "extreme climate year" compare to its impact on an "average climate year"?

We thank the referee for this question, that let us to better clarify this aspect. We choose 2015 for two aspects: 1) Because it was an “extreme” warm meteorological year for which we could test our methodology in conditions that are more and more frequently happening in the last decades and that will be the “normal” in the next future; 2) it is also useful to  the companion paper that investigates the vegetation effects on air quality since 2015 is a reference year for air quality assessments at national level in many countries (Italy and Spain in this case) as required by the Air Quality Directive.

To clarify these aspects, we added some explanatory text and references in Section 2.

• The data in subsection 2.2.2 does not specify which urban vegetation was taken for analysis. The first thing we want to know is how much total green space there is in each of these cities and what percentage of that total city area is made up of green space. What tree and shrub species are prevalent in a certain city. How fragmented the greenery is. What primary forms of vegetation are represented by green areas (forests, artificial stands, parks, squares, and shrubs)? All these green space criteria determine how much they can affect climatic factors.

We thank the referee for raising this point. We added some text at the end of subsection 2.2.2 which refers to the companion paper Mircea&D’Isidoro (TableS3 and FigureS3) where more details on prevalent vegetation species and coverage are provided for the three cities.

• Numerous water bodies (rivers, canals, lakes, and ponds) may be found in these cities. For instance, consider the rivers Manzanares, Reno, Savena, and others, which have woody vegetation growing on their banks (as a component of the city's green areas). Due to their cooling effect throughout summer, water bodies have a considerable impact on microclimatic indicators. Did the authors consider this fact in their calculations? How were the impacts of water bodies and vegetation on changes in meteorological indicators divided?

Thank you for the question. The WRF meteorological model does consider the presence of different landuse types, including water bodies, in the computation of latent and sensible heat fluxes at the surface. This means that the effect of water bodies is considered in the numerical simulations. Nonetheless, as we were interested to evaluate the effect of urban vegetation, it was out of the scope of our work to isolate the contribution of water bodies as well as that of green areas with no prevalence of urban fraction within the municipality. This means that when performing VEG and NOVEG simulations, we only changed vegetation inside grid cells where urban fraction prevails (“urban vegetation” and “urban cells” in the text, respectively), letting the rest unchanged. This is for instance the case of the hills south of the Bologna municipality and the “Monte del Pardo” green area north of Madrid (see Figure 2), for which vegetation was let unmodified in both simulations. This study paves the way to further detailed investigations of water body effects as NBS on both meteorology and air quality considering a realistic representation of vegetation.  Definitely, it will be interesting to analyse them in the context of city’s peculiarities.

• The calculations were performed using grid cells with a size of 1 km by 1 km. How logical is the selection of such a big grid cell size? Do the authors think that vegetation impacts meteorological indicators over such a wide range (i.e., up to 1 km from green areas)?

Thank you for this comment, that allows us to clarify this aspect.

To answer to the first question, there are essentially two motivations for the resolution choice: 1) going to more refined resolutions (e.g., meters to tens of few hundred meters) would have required another kind of meteorological model than a mesoscale one, with the need of huge/unaffordable computational time and storage space; 2)  Moreover, as we tested our methodology also to evaluate the impact of vegetation on Air Quality in the cities (companion paper Mircea&D’Isidoro, 2023), currently there are not numerical models that can afford full atmospheric modelling (atmospheric chemistry and all related physical/chemical processes) at city scale

Therefore, a resolution of 1 km is a good compromise for assessing the effects of vegetation both on meteorology and air quality including all atmospheric processes that regard also pollutants formed in atmosphere such as ozone (O₃).

To answer the second question: even if the simulated quantities represent an average on the given grid cell, the numerical model “sees” the sub-grid vegetation type and distribution and urban texture and takes this information into account when computes atmospheric dynamics and thermodynamics processes.  The effect of vegetation change in each cell can be advected and influence surrounding areas as we show in Figure 5.  

• Technical issue

Please use the same terminology throughout the text. Simply use Milan or Milano as the city name.

Done. Thank you for notifying this.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The authors revised the manuscript with consideration of all comments and suggestions. I believe the manuscript can be accepted for publication.