Please find my detailed commentary attached. 

This study undertakes a systematic literature review with the aim of creating a vulnerability functions database for evaluating critical infrastructure (CI) in the face of multiple hazards. While the subject matter is intriguing, the manuscript suffers from unclear methodology and lacks a clear rationale for the study. Several major concerns need addressing before considering the manuscript for publication.

Major comments

1. The study builds upon the argument of a deficiency in a centralised repository of vulnerability functions for assessing CI against multiple hazards. However, the introduction lacks a thorough examination of how this absence hinders researchers or practitioners. The discussion in the third paragraph primarily focuses on distribution and formatting issues of existing functions, neglecting considerations of resolution, adaptability, and transferability, which may have more significant impacts. It is recommended that the authors critically assess the implications of the current state of vulnerability functions.
2. The use of the term "multi-hazard" in the title appears vague, with potential differences between "Multi-hazard" and "multiple hazards." The authors should either redefine "multi" in the title or refocus the article exclusively on multi-hazard events. If opting for the latter, reference to relevant articles (a few suggested below) for clarification on the definition of multi-hazard events is encouraged.

https://doi.org/10.1016/j.scitotenv.2023.169120

https://doi.org/10.1038/s43017-020-0060-z

https://doi.org/10.1002/2013RG000445

1. Referring the statement ““We conducted a literature search for CI vulnerability to flooding, earthquakes, windstorms and landslides over the period January 2022 to March 2023 by systematically using combinations of keywords on the general concept of hazards, critical infrastructure and vulnerability” in section 2.1, methodological concerns include the choice of four specific hazards, the short 14-month (January 2022 to March 2023) search window, and ambiguity regarding whether an established approach like the PRISMA Protocol was followed for the systematic literature search. The authors should specify the databases considered (e.g., Scopus, WoS, PubMed) and provide the search term syntax. Additionally, the number of initial references found, inclusion/exclusion criteria, and handling of duplicate references should be clarified.
2. Referring the statement “We excluded bridges from our database as there is an excessive amount of bridge literature that deserves a review article on its own” in section 2, the exclusion of bridges from the database lacks a clear rationale, merely stating there is an excessive amount of bridge literature deserving a separate review article. A more explicit justification or reconsideration of this decision is necessary.
3. The temporal discrepancy between the search window (January 2022 to March 2023) and data in Figure 1 (1984-2023) raises confusion. The methodology lacks clarity on whether vulnerability functions were extracted from literature or other sources. A comprehensive methodology section, including a flow diagram, is needed to elucidate the study's process.
4. The unclear methodology and data sources undermine the meaningfulness of the results at this stage.

Minor comments

1. In the abstract, the phrase "essential vulnerability information for CI" requires clarification.
2. The statement, "even within these non-public databases, CI is often limited represented," lacks clarity and needs rephrasing for better understanding.

This is an invaluable study for those engaged in the risk analysis of critical infrastructure for natural hazards. The paper is very well organised and includes a systematic literature review and an extensive database of fragility and vulnerability models, and associated costs for various types of infrastructure, while bridges are excluded due to the excessive amount of bridge literature. The following comments are provided:

It is suggested adding the parameters of the fragility functions when possible (e.g. median, standard deviation when a lognormal distribution is adopted).

It is suggested adding in the database the following fragility functions:

Fragility functions for tunnels (earthquakes, and ageing effects):

Argyroudis, S. A., Pitilakis, K. D. (2012). Seismic fragility curves of shallow tunnels in alluvial deposits. Soil Dynamics and Earthquake Engineering, 35, 1-12.

Huang, Z. K., Pitilakis, K., Tsinidis, G., Argyroudis, S., Zhang, D. M. (2020). Seismic vulnerability of circular tunnels in soft soil deposits: The case of Shanghai metropolitan system. Tunnelling and Underground Space Technology, 98, 103341.

Argyroudis, S., Tsinidis, G., Gatti, F., Pitilakis, K. (2017). Effects of SSI and lining corrosion on the seismic vulnerability of shallow circular tunnels. Soil Dynamics and Earthquake Engineering, 98, 244-256

Huang, Z., Argyroudis, S., Zhang, D., Pitilakis, K., Huang, H., Zhang, D. (2022). Time-dependent fragility functions for circular tunnels in soft soils. ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems, Part A: Civil Engineering, 8(3), 04022030.

Tsinidis, G., Karatzetzou, A., Stefanidou, S., Markogiannaki, O. (2022). Developments in seismic vulnerability assessment of tunnels and underground structures. Geotechnics, 2(1), 209-249.

Fragility functions for retaining walls/abutments (earthquakes):

Argyroudis, S., Kaynia, A. M., & Pitilakis, K. (2013). Development of fragility functions for geotechnical constructions: application to cantilever retaining walls. Soil Dynamics and Earthquake Engineering, 50, 106-116.

Fragility functions for embankments (flood, scour)

McKenna, G., Argyroudis, S. A., Winter, M. G., & Mitoulis, S. A. (2021). Multiple hazard fragility analysis for granular highway embankments: Moisture ingress and scour. Transportation Geotechnics, 26, 100431.

Tsubaki, R., Bricker, J. D., Ichii, K., Kawahara, Y. (2016). Development of fragility curves for railway embankment and ballast scour due to overtopping flood flow. Natural Hazards and Earth System Sciences, 16(12), 2455-2472.