Understanding and Assessing Climate Change Risk to Green Infrastructure: Experiences from Greater Manchester (UK)

Comment

Our response

1.The abbreviation "GI" should be defined the first time it is mentioned, rather than waiting until Section 2, the Literature Review. It would be beneficial to include a more detailed definition of urban GI, perhaps with some categories or examples.

The GI has been defined at the first point that it is used. Urban GI has also be discussed within the literature review, including the identification of different types of urban GI.

2. When discussing disaster risk reduction, it would be pertinent to mention the i-Rec Conference in Japan, a significant milestone in discussions on urban resilience and disaster risk reduction.

We explored this conference with interest. However, we have not referenced it specifically, and believe broader reference to the connection between GI and disaster risk reduction is appropriate for this paper as this addresses the specific point we are looking to make of positioning GI as a form of critical infrastructure.

      3. In the Literature Review, the authors note that “There is also a growing literature focused explicitly on understanding how climate change and extreme weather impact urban trees.” (Line 154). Could the authors clarify whether trees have been recognized as an important component of GI, and explain their significance?

Urban trees are highlighted as an important component of urban GI due to the multiple ecosystem services that they provide, with an associated supporting reference on this topic included.

4. In Section 3.1, Case Study Scope and Focus, including a map of Greater Manchester (GM) would help clarify the texts.

We have included a new map that shows the location of GM within England, and also illustrates where grasses are present within GM.

5. A table comparing trees and grass would provide clearer distinctions and facilitate easier understanding.

While we agree with the reviewer that comparing trees and grass would provide an easier understanding regarding how they respond to water stress, habitat fragmentation, and groundwater extraction abilities, unfortunately, there are so many tree and grass types available, and they usually have varying capacities. Our dataset only indicates the location of tree or grass patches and does not provide specific details of the type of trees or grass. In our analysis, we assumed the grass type as amenity grass based on previous evidence, but such a generalized assumption is not realistic for trees. Considering such limitations of the data, a direct comparison between trees and grass is not feasible within the scope of this study. However, to reflect the difference in capacities between trees and grass, our text clearly indicated that trees are more resilient to hazard exposure than grass. We hope such clarification indicates how they are different. Additionally, in the discussion section, we noted this as a limitation of the paper and called for future studies comparing different GI types.

6. In the Conclusions section, the significance of this research is extensively discussed, but some meaningful conclusions are briefly mentioned. For instance, the study introduces a "transferable risk assessment methodology that can be adapted to other GI planning contexts." It would be helpful to outline briefly the key steps of this methodology.

The transferable risk assessment methodology is briefly outlined in the conclusion section, summarizing the approach applied to assess risk to GM’s grassed areas from low water availability.

Comment

Our response

1) The title should be completed specifying the special focus of the research work done on urban grasslands. It is too general now.

The title has been modified and expanded to – Assessing climate change risk to urban green infrastructure: learning from an assessment of risk to Greater Manchester’s grasslands from low water availability. This reflects the objectives of the paper, which have been clarified in the introduction.

2) The introduction mentions "future proof urban landscapes to climate change" and "environmental functionality". The manuscript presents the research work done regarding the current situation in Manchester, and should include among its objectives more specific recommendations about how to improve environmental functionality in the future. The Introduction section should present in a very clear way, which were the goals/ research questions and delimitations of the research work done. Also the abstract should be revised.

The research scope and objectives have been more clearly defined in the abstract and introduction. Here we have clarified that one of the goals of this paper is to discuss how GI risk assessments can inform and contribute to GI planning. The objective is not to discuss approaches that can be applied to improve environmental functionality of grasslands (and GI more broadly) in the face of the changing climate - this is beyond the scope of this paper, which is emphasised in the introduction and discussion. Such actions are nevertheless needed – what this paper does is to highlight an approach where such activity could be prioritised guided by the risk assessment. Further, we have replaced the term ‘Environmental functionality’ with ‘ecosystem functionality’ to fit with the conceptual approach that guides the paper.

3) The Introduction section does not mention the urban grasslands as the main focus of the text. This should be corrected.

We have made it clearer that the focus of the case study, and the outcomes of the empirical research, is on urban grasslands, through the connection to the GM case study on this topic. We have also clarified in the introduction that a broader aim of the paper is also to discuss the current status of academic research on extreme weather and climate change risk to urban GI, which is achieved through the literature review. Further, establishing the current status of academic research helps to set the foundations for the empirical research. Also, in doing so, we aim to help to raise awareness of this under-researched topic.

4) The Literature review section mentions urban trees and forests, though the research work presented does not include information about these topics. On the other hand, the main focus on urban grasslands is not sufficiently highlighted as the main topic. 

As outlined in our response to comment 3 above, our aim for this paper is to also increase awareness and understanding of climate change risk to urban GI, and the status of current research on assessing risk in this context, much of which focused on urban trees and forests. The clarification of the aims of the paper now makes this clearer. We have also clarified the focus of the empirical research on urban grasslands within the literature review. Here, (as noted in the response to comment 5 below) it is apparent that there is limited research on urban grasslands in the context of climate change and extreme weather impacts and risks. This provides a justification for the case study focus.

5) The Literature review should be compacted and revised. It includes information that is obvious or not necessary to explain the further case study. It should be more focused on the urban grasslands.

We have condensed the literature review, removing sections of text in several places, and have focused this section on the core themes underpinning the paper. We made a further extensive search of the literature and could find very little on the topic of assessing extreme weather and climate change risk to urban grasslands. We have emphasised this within the literature review, and have included one additional reference (Norton et al 2016), although this does not link directly to urban areas.

We have aimed to refine the literature review section and make closer links to the core objectives of the paper. However, as noted above, and clarified within the objectives as set out in the introduction, one of our goals is to include a broader commentary, within the literature review, on the current status of literature on themes linked to climate change risk and risk assessment in the context of urban GI. We believe that given this is an under-researched topic, that this paper provides a useful contribution in this respect, which also sets up the empirical work on urban grasslands in GM. We also believe that positioning this discussion in the context of urban critical infrastructure, and therefore introducing related themes in the literature review, is needed to support the narrative presented within the paper.  

6) The concepts of hazard and adaptative capacity should be specified. How can their assessment be applied to the case of Manchester?

Page 4 addresses this comment, with examples of hazards now included, and adaptive capacity defined. Section 3.2.1 provides a detailed discussion of low water availability, and clarifies that this is the hazard considered within the GM study. Section 3.2.2 clarifies how adaptive capacity is applied in the GM case, utilising an indicator on groundwater depth.

7) How do the non-linear social-ecological systems appear in the Manchester urban grasslands? How do they impact their sustainability?

We could not clearly understand the nature of this comment, and have therefore not addressed it in the submitted version.

8) Which are the specific amenity grasses used in Manchester urban grasslands? The analysed grasslands do not have any shrubs or trees? Why their impact in the results is not mentioned?

Specific information on the amenity grasses used in GM’s urban grasslands is currently unavailable. From our local knowledge, they usually include species such as Perennial Ryegrass, Chewings Fescue, Poa pratensis, which have been referred to in the methodology section. But our dataset does not specify which grass type is present in specified locations, and such detailed data is not available for the study area. Instead, we utilized Gill et al., 2013 assumption about common amenity grass in GM area, and followed the calculation based on the same assumption.

Regarding the second point about “grasslands do not have any shrubs or trees?”, in the land cover data that we utilised for this study, locations where there is mixed vegetation classes are identified, where grass below large trees might not therefore be recognized (Denis et al., 2018). Consequently, there may be some grass patches below trees which have missed from the risk estimation process. However, given that land cover dataset that was utilised for this study has a 10m spatial resolution, and classified grass as a specific cover type, the majority of GM’s grass patches (distinct from those areas that represent a mixture of grass and shrubs for example) were accounted for in our modelling process. Further, we argue that the omission of certain grass patches due to obstruction of trees does not change the overall findings presented within in this study. However, we have reflected on this issue in our discussion section and suggested that further research on this topic is needed to clarify this issue.

9) It would be important to specify in the results the relationship between the grass and soil type, and evaportranspiration, etc. factors, as this data would be very important for future planning of GI.

This is a valuable comment which we have addressed in the revised submission. In this case, we assumed all amenity grass type has same evapotranspiration rate, hence, the values we estimated are mostly a function of soil type, root zone water availability (RZAWC), limiting deficit (LIMDEF), and soil water deficit values. We have noted in the results that, RZAWC and LIMDEF contributed the variations in observed ETo loss observed in Figure 2, and have included a new supporting table (A1) in appendix, and have discussed this issue further in the first paragraph of the result section. 

10) Regarding water availability, water recycling could be recommended?

As noted in the response to comment 2, we have clarified that one of our objectives for this paper is to discs how climate change risk assessment can inform GI planning, rather than discussing ways that GI (in this case urban grasslands) can be adapted to climate change.

11) The socioeconomic deprivation conditions In Manchester are not clearly explained and their impact in urban grasslands specified.

Further details of the IMD dataset is provided in section 3.3, with the diversity of GM’s neighbourhoods also highlighted in this context. The connections between socio-economic deprivation and the functionality of urban grasslands (and GI more broadly) are more clearly expressed in section 5.

12) The pluvial flood risk and its causes are not explained, nor how the combination of various urban hazards detected may menace the urban grasslands.

Pluvial flood risk is defined in section 5, with the impact of low water availability on the capacity of urban grasslands to provide flood risk benefits highlighted.

13) The discussion should be more punctual and specific, now it is very general. It also should be compacted.

We have refined and shortened the discussion section as recommended, connecting specifically to the objectives for the paper outlined in the introduction, and introducing closer connections to the empirical research presented in the paper.

14) Conclusions should offer responses to the research questions presented and give more specific suggestions regarding the mitigation of the effects of the climate change in the urban grasslands of Manchester.

Within the conclusion, we clarify the main outcomes and findings of the paper, with more reference to the GM case study. As noted in response to comments 2 and 10, this paper about risk assessment in particular. We highlight in the discussion that risk assessment can inform the implementation of adaptation responses, although discussing these responses is not the primary focus of the paper.

Comment

Our response

The methodology is complex, gathering various types of data, which may hinder the replicability of the study in other cities that may not have access to such data.

We agree with this comment, and have added further discussion on the difficulty of accessing and/or developing certain data sets to undertake the risk assessment in practice.

The focus on grassed areas is certainly interesting and well-justified, but I wonder if future research could also include both shrubs and trees. Would it be possible to expand the scope? What specific challenges and opportunities might arise from such an expanded scope?

This is a useful suggestion. Issues and challenges concerning implementing the risk methodology for trees and shrubs have been presented in the discussion section.