This paper presents an overview of the main mechanisms associated with heavy precipitation over the Mediterranean. In particular, it reviews the main outcomes from the HyMex international project and their field campaigns. 

After a general introduction and a description of the observational and modelling infrastructure, the paper encompasses many of the key mechanisms leading to heavy precipitation. In general, all mesoscale and microphysical aspects are very well covered with the correct highlight of the results coming from the HyMex observation campaign. 

The only aspect which in my view could have been further expanded, given also the relevance in the genesis of heavy precipitation, is their relation with the large-scale dynamics (section 3.1). Amongst the important literature on this topic, like Massacand et al. 1998 and Martius et al. 2008, it is worth mentioning a few very recent papers like 1) De Vries 2020, 2) Mastrantonas et al. 2021, 3) Grazzini et al. Part II 2021, which are showing robust and quantitative relations and dynamical linkages with large-scale precursors. But I understand that the focus of the current review is more on the mesoscale and local interaction so take my suggestion as not compulsory but as a simple indication. You decide whether it is necessary to expand the section. Other than that I think the manuscript is ready for publication after very minor changes reported below.

Minor changes:

- On page 9, line 291, you mention "comma-shaped" cloud coverage. You did not explain the meaning but hinting some implication of that. The explanation comes later, on pages 10 lines 324-327. It would be preferable to introduce first the relevant concepts.

- For the benefit of readers non used to European geography, it would be helpful to show CI, NEI, CO regions (only defined in the text) delimited on a geographical map

References:

1) Vries, A. J. D., 2020: A global climatological perspective on the importance of Rossby wave

breaking and intense moisture transport for extreme precipitation events. Weather and Climate Dynamics. 

2) Mastrantonas, N, Herrera-Lormendez, P, Magnusson, L, Pappenberger, F, Matschullat, J. Extreme precipitation events in the Mediterranean: Spatiotemporal characteristics and connection to large-scale atmospheric flow patterns. Int J Climatol. 2021; 41: 2710– 2728. https://doi.org/10.1002/joc.6985

3) Grazzini, F, Fragkoulidis, G, Teubler, F, Wirth, V, Craig, GC. Extreme precipitation events over northern Italy. Part II: Dynamical precursors. Q J R Meteorol Soc. 2021; 147: 1237– 1257. https://doi.org/10.1002/qj.3969

General aspects

The paper “Overview towards improved understanding of the mechanisms leading to heavy precipitation in the Western Mediterranean: lessons learned from HyMeX”, by Samira Khodayar et al. is a good review about the present understanding of the heavy precipitation in the Western Mediterranean, mostly oriented to work recently done in connection with the field phase “SOP1” (2012) of the “Hydrological cycle in the Mediterranean Experiment” (HyMeX), but also including references to research about the matter, not strictly based in HyMex; even significant work done before the HyMeX initiation is referenced here. By this way a more complete vision about the problem is achieved.

This review is not the first about HyMeX-SOP1, but it is timely now, because 2020 was indicated as the end of HyMeX. Ducrocq et al (2014), can be seen as an initial review, and a special issue (2016) of the Quarterly Journal of the Royal Meteorological Society, introduced by Ducrocq et al. (2016; https://doi.org/10.1002/qj.2856), can be considered as a second one. In any case, since 2016 to present days’ significant research results have been added.

A positive aspect of this review is the team of authors that has been formed: their different specialisations cover many aspects of the problem and this permit a wider and also more precise vision of it.

The number of commented references is really large. The list of references occupies more than 24 pages of a total of 63 pages. This means a hard and valuable work, but the list of references is not complete. In fact, it would be almost impossible to construct a complete list.

In summary, I consider this paper is good enough, it is useful and it is an interesting tool to face the problem of the West-Mediterranean heavy rain in many aspects, and therefore I recommend its publication, almost as it is. In the following there are a few comments that can be taken into account by the authors, although the consideration of all of them is not strictly mandatory to publish the paper.

Details

-Line 154 mentions 16 IOPs during the campaign SOP1: the total of IOPs was 20 (see Ducrocq et al, 2014)

-The measurement site named BA (Balearic Islands) not only included Menorca (were specific facilities were installed), but also Mallorca, with operational radar and radio-sounding stations (lines 180-181)

-In figure 1, I don’t understand what the colour of each radar station means

-By line 320, it seems that the authors consider that only breaking Rossby waves (cut-off lows) can induce Mediterranean cyclogeneses, but also open troughs can do it

-Fig. 2a, b. The meaning of the colours is not clear to me

-In section 3.2.1, another interesting reference for water origin of heavy rain in Western Mediterranean is Insua-Costa et al (2019; https://doi.org/10.5194/hess-23-3885-2019)

-With regard to section 3.3.1, IOP8, the most important event that affected Spain during SOP1, and also IOP15 and others, are analysed in Jansà et al (2014; https://doi.org/10.3369/tethys.2014.11.03). [Note also that Ferreti et al (2014; https://doi.org/10.5194/hess-18-1953-2014) is a parallel paper on the cases that affected Italy]

-Regarding section 3.3.2, the convergence associated to a cold pool boundary was already highlighted as a continued triggering convection mechanism in Western-Mediterranean heavy rain in Ramis et al (1994; https://doi.org/10.1002/met.5060010404)

-Fig. 6 is not clear enough to me

-With regard to section 4.3, the Arome-WMed reanalyses, made with assimilation of all available added observations, permitted to detect a secondary cyclone that produced severe weather in Menorca during IOP18. See Carrió et al (2020; https://doi.org/10.1016/j.atmosres.2020.104983)

-Continuing with 4.3, Campins et al (2016; https://doi.org/10.1002/qj.2737) studied the impact in the forecasting of the assimilation of some extra observations during SOP1