Review of "The evolution of precipitation and warm conveyor belts during the central southwest Asia wet season" by Melissa L. Breeden, Andrew Hoell, John R. Albers, and Kimberly Slinski

General comments:

The present study by Breeden et al. investigates the seasonal evolution of precipitation over southwest Asia and the link of precipitation to warm conveyor belts and ENSO. The study first extensively compares different precipitation data sets and finds good agreement in terms of the timing of the peak precipitation. However, the data sets disagree concerning the precipitation amounts. The study continues with an analysis of the seasonal evolution and the comparison of days with little and heavy precipitation. Overall, the methods are sound, the text is well written, and the figures are clear. However, many of the conclusions remain rather vague and it is not upfront clear what the main novelty of the study is. Suggestions for further investigations that may help to strengthen the conclusions and to make this study distinct from other previous studies are given below.

Major specific comments:

1) I fully understand the authors' motivation to investigate the link of WCBs to precipitation since these are one of the most important rain producing system in midlatitudes. That being said it seems that other weather systems may be of similar or even larger importance in CSWA. For example, the climatological WCB frequency in Fig. 6 is mostly less than 8% and even during the 'wet' days the difference is only on the order of 25%. This makes the reader wonder which other rain producing systems are responsible for precipitation in the region (especially during wet days). At least a critical discussion of the potential role of other weather systems should be included in the manuscript.

2) The authors conclude that the modulation of WCB frequency by ENSO clarifies "the link between low-frequency circulation changes that ENSO produces, and the transient, short-lived nature of precipitation in this region". Though I generally agree with this interpretation it remains unclear whether it is the WCB frequency alone that leads to a reduction of precipitation or whether the WCBs that occur are associated with increased/reduced precipitation. To answer this question the authors may want to adapt an established approach (e.g., Catto et al. 2012, Hauser et al. 2020) that decomposes rainfall anomalies into changes in intensity and frequency.

3) Though the statistical link between ENSO and WCBs is clear, it remains unclear what the physical connection may be. Is the number of WCBs increasing during El Nino due to planetary Rossby waves excited by the tropical convection? Is the number enhanced due to higher SST that increase moisture in WCB inflow regions? Some explanation and analysis which establishes the dynamical link between ENSO and WCB activity in CSWA would definitely help to strengthen the conclusions. This is particularly necessary as other studies have investigated dynamical links between ENSO and CSWA rainfall (see introduction) and it is not clear what additional insight the present study provides.

Minor specific comments:

Title: To me, it is not upfront clear that "the evolution" means "the seasonal evolution". My suggestion is therefore to specify that the seasonal evolution is meant. Also, I am wondering whether it would be beneficial to specify that the study also considers quite extensively the variability of precipitation.

l. 14: I find it confusing that WCBs are chosen to represent "local vertical motion forcing". In my view, WCBs are rather a result of local vertical motion forcing than a representative of forcing. Perhaps just leave out the word "forcing"?

l. 19: The sentence "Precipitation intensity, duration, and the associated circulation patterns evolve...." remains quite unspecific. Be specific on how exactly they evolve/change as winter progresses. Clear statements will make it easier to identify the main conclusions and likely increase the visibility of the study.

l. 19: It would be helpful to indicate that it is the area-mean daily accumulation.

l. 21: What is meant with "heavy precipitation days"? Is this referring to days when the accumulation exceeds 4 mm? Please specify.

l. 23: The reader may wonder what is meant with "neither precipitation nor WCB change". Does this refer to intensity, duration or frequency changes? Please clarify.

l. 45: Rather use em-dashes than en-dashes.

l. 73: Is past-tense used on purpose here? In my view, present tense could be used in this and the following sentences as well.

l. 87 and elsewhere: Use en-dashes to indicate ranges between two values.

l. 87: Are the precipitation data sets used at their native grid spacing or is any kind of remapping performed?

l. 89: Can you specify how many rain gauges are actually located in Afghanistan? "Relatively few" is rather vague.

l. 92: Is ERA5 (and JRA55) really incorporating satellite-derived precipitation estimates? To my understanding, ERA5 precipitation is based on short-range forecasts of ECMWF's IFS system. Thus, the total precipitation in reanalyses is the sum of large-scale precipitation generated by the cloud scheme and convective precipitation generated by the convection scheme. To my knowledge precipitation estimates are only assimilated over the United States from 2009 onward.

l. 99: Can you provide some specific information concerning the number of stations in the country?

l. 103: What is the motivation for using a coarser resolution for streamfunction than for IVT?

l. 115: It would be very helpful to provide this information right at the beginning of section 2.1. Otherwise, the reader may wonder what the exact time period analysed in this study is.

l. 119: Does "probability curve" mean "probability distribution"/"probability density function"?

l. 135: Can you elaborate on why a coarser resolution would lead to higher means and standard deviation?

l. 143/Fig.3: Are the values accumulated over the entire period 1981-2020? If so would it not be easier to understand if you showed mean precipitation per month?

l. 180: I had difficulties to find the corresponding figure in Pfahl et al. 2014 showing the correspondence of precipitation and WCBs during spring. Just out of curiosity could you indicate the corresponding figure?

l. 180: "heavily related" is a rather qualitative statement. Could you indicate what percentage of precipitation is roughly related to WCBs? My interpretation of Fig. 7b in Pfahl et al. 2014 is that roughly 50% of precipitation in Afghanistan is linked to WCBs.

l. 247: Can you comment on how El Nino is linked to strengthened synoptic activity and moisture availability? I assume that global teleconnection patterns play an important role.

l. 257: Please double-check the usage of past and present tense.

l. 270: Can you comment on the moisture availability in this region which potentially effects the ascent of WCBs?

l. 278: As before it would be worthwhile to comment on how ENSO is dynamically linked to rainfall in CSWA.

l. 282: On a local scale I agree with this interpretation. But what circulation change modulates the occurrence frequency of WCBs in first place?

References:

Catto, J. L., Jakob, C., and Nicholls, N. (2012), The influence of changes in synoptic regimes on north Australian wet season rainfall trends, J. Geophys. Res., 117, D10102, doi:10.1029/2012JD017472.

Hauser, S, Grams, CM, Reeder, MJ, McGregor, S, Fink, AH, Quinting, JF. A weather system perspective on winter–spring rainfall variability in southeastern Australia during El Niño. QJR Meteorol Soc. 2020; 146: 2614– 2633. https://doi.org/10.1002/qj.3808

The evolution of precipitation and warm conveyor belts during the central southwest Asia wet season

This manuscript contains a study that focuses on wet-season precipitation over Afghanistan on a daily scale, investigating the association of heavy precipitation days with the presence of warm conveyor belts (WCBs) and the link with climate modes such as ENSO. The manuscript is well-written and the analysis is clear and logical. However, there are a few primary questions I would like to be addressed before it can be accepted for publication. Those questions are listed below, followed by minor line-by-line comments.

Primary Comments:

- My understanding is that the key novelty of this manuscript, that sets it apart from the previous papers on the topic, is the focus on a daily time scale, rather than monthly or seasonal, for precipitation. If this is the case, then a more detailed analysis needs to be performed on what the causes of precipitation variability at such a time scale are. WCBs are airstreams that are part of weather systems such as extratropical cyclones. Basing the analysis on WCBs without looking at what systems they are associated with makes the analysis incomplete. It is argued in the conclusions that the analysis of cyclones’ lifecycle and their changes throughout the wet season could be a future avenue of research, but I would rather suggest that this activity (even in an exploratory way) is used to complement the present manuscript. “Westerly disturbances” are mentioned at several points in the text. Are they the same western disturbances as in Hunt et al., 2017 (https://doi.org/10.1002/qj.3200) and following papers by the same first-author (and I should specify I am not him or any of his co-authors)? How does their structure and evolution changes throughout the course of the season? Without answering these questions, analysing WCBs alone leaves many questions open on what mechanisms could be responsible for the changes in precipitation shape between months. For example, looking at Figure 5, the frequency of WCBs over Afghanistan in Feb and April is very similar. There must then be other factors behind the different behaviour in precipitation.

- As said above, it is argued in the manuscript that heavy precipitation is associated with WCBs, which are linked to systems such as extratropical cyclones and to the pattern of the upper-level sub-tropical westerly jet. Therefore, without discounting the importance of ENSO, it would make sense investigating also the link with climate modes more directly related to the Eurasian circulation at these latitudes (NAO, CGT, …).

- Given the location of the area under study, with several mountainous areas in it and at its edges (including the very high Hindukush – Karakoram range), it would appropriate to consider the impact of orographic effects on precipitation.

- Wet-season precipitation in the area is often described as sporadic. However (lines 147-148) is having up to 6 days per month with precipitation over 4 mm really “a reflection of the intermittent and intense nature of precipitation” and of it being sporadic ? It does not seem a small number to me. Could you help putting this into context by comparing values against other regions in the world where precipitation is known to be less intense, intermittent, and sporadic and more regular and frequent? (You could start doing this in the Introduction by looking at relevant literature and then use that discussion as a reference while commenting the results)

Minor comments, line-by-line:

Line 36: We are moving beyond the science here, but looking at the recent history I don’t think “humanitarian food aid is provided to the country [Afghanistan]” solely “given the crucial but unreliable role that precipitation plays in the region”. A few words mentioning general geopolitical context would help.

Line 44: Is this statement referred to precipitation globally or in the CSWA region? Please specify.

Line 52: I am not disputing the expertise of the authors of the present paper, but it would be appropriate to add here more studies that they are not authors of. At the same time, I would suggest considering more teleconnections (see related general comment).

Line 74-81: I would limit this paragraph to a short summary of what the following sections contain, without mentioning the results here (such a discussion would better fit to the “Discussion and conclusions” section).

Line 104: Please define IVT (What’s its mathematical expression? What levels are used? …) or point to a reference. Also, the word “’horizontal” does not seem to be in the right place here. If it indicates that moisture flux is calculated using horizontal wind, I would insert it between “integrated” and “moisture”.

Line 130 - Fig 1: Mountain ranges near Afghanistan (Hindukush – Karakoram to the E and Pamir, I think, to the N) are characterised by large precipitation amounts, as shown in the panels of this figure. What are the reasons for not including them in the domain under study? I understand your focus on semi-arid Afghanistan’s climate and I am not asking you to widen the domain, but I think that a  short discussion on whether precipitation in those mountainous areas is then collected in river basins crossing Afghanistan or not should be included.

Figure 2: CPC is not mentioned in the caption.

Figure 3: Please increase font size in legends, axes, and on top of bins (no more than 1-2 decimal digits are needed), as numbers are difficult to read.

Figure 3: I would say “average number of days per month” rather than “per year” in the caption (as it is already clear that this is over 1981-2020).

Figure 3: Please give more details on what “cumulative” means. Is this cumulated over all years and averaged over the area? Or cumulated over the area and average over all years? Or something else?

Lines 154-155: What is the definition of an individual precipitation event? How long does the no-precipitation time has to be to separate two distinct events?

Line 169: Where do I see 12 mm accumulation in Fig 4? There does not seem to be a “total event accumulation” contour in the figure

Figure 7: in the caption, shouldn’t it be “contoured at +/- 0.05, starting at 0.1”? Otherwise, I am not sure I understand what WCB frequency values are shown. Also, it is rather difficult to see the green dashed contours.

Line 224: Is it “lack of significant tropical Pacific SST anomalies associated with…”?