Review of “Consistent increase of East Asian Summer Monsoon rainfall and its variability under climate change over China in 34 coupled climate models” by Anja Katzenberger and Anders Levermann

General Comments: In this paper, the authors examined the future changes in the mean precipitation over the EASM region as well as its variability under different emission scenarios. Their analysis suggest that both mean precipitation and its variability are increasing under all emission scenarios, with a stronger response under stronger emission scenarios. There were many studies using CMIP5/6 model simulations that looked at the precipitation changes over different monsoon regions of the globe. Also, they find that the “wet-gets-wetter” arguments holds true for EASM region. Overall, the types of analyses presented in this paper are useful for regional climate change assessments. I have some specific concerns that need to be addressed before accepting the article.

Specific comments:

1. My major concern in this paper is the way in which the models are grouped. I don’t have any issues with the “Group A” models which have a mean precipitation withing +/- 2 std of the observations (reanalysis). However, the Group B cosists of the models in both sides of the extremes. This means that the when you take ensemble mean, you are averaging the outliers on two sides and as a result there may not be any use of grouping the models in this way. You may either focus on the Group A models or have three groups (one group each for outliers on each side).
2. It would be interesting to see the seasonal mean circulation changes as well. This will give a better understanding of the changes in the underlying dynamics
3. The “wet-getter-wet” argument is not new. If you can look at the thermodynamic and dynamic components of the precipitation change, it can give a better insight.

General comment:

This study examined future changes of East Asian Summer Monsoon (EASM) including seasonal mean precipitation, interannual variability and extreme wet seasons using CMIP6 models. According to the simulated magnitude of regional, seasonal mean precipitation, the CMIP6 models are divided into two groups. The projections are then based on the group of models with reasonable magnitude of EASM precipitation. It is shown that mean precipitation, interannual variability and extreme wet seasons of EASM will increase in the future under different SSP scenarios.

However, the current analyses lack significance and robustness in a few aspects.

Firstly, many methods are inappropriate. (1) The model evaluation is based on regional mean and seasonal mean precipitation over East Asia. But the EASM is a complex system, in which the monsoon circulation and spatial pattern of precipitation is very important. Hence this evaluation metric is insufficient to represent the EASM, which means that the model selection is not robust. (2) Reanalysis, rather than observational data, is used to evaluate the model simulated precipitation. As there are many observational datasets (e.g., APHRODITE, GPCC, GPCP) in East Asia, they should be used for model evaluation. (3) As the focus is the EASM, the EASM domain could be defined more appropriately, taking into account many proposed definitions in previous studies. (4) Significance test for projected changes needs to be included. These limitations in methods weaken the robustness of the results.

Secondly, no physical understanding is provided at all. The study focuses on model simulated change in regional mean EASM precipitation, but no physical understanding of EASM change is provided.

Most importantly, the scientific question needs to be refined in order to improve our current knowledge about EASM change. There have been plenty of papers investigating the future changes of EASM covering a wide variety of aspects, including process-based projection, spatial pattern of precipitation change, thermodynamic and dynamic processes of monsoon precipitation change, changes in monsoon duration, northern boundary, extremes (see a few references below and references therein). For example, based on CMIP6 multi-models, there is dynamic-based projection of EASM rainfall and variability (Xue et al., 2023), projection of monsoon rainfall and duration with thermodynamic and dynamic understanding (Moon and Ha, 2020; Ha et al., 2020). Overall, these studies so far have provided a relatively robust understanding of future EASM change based on GCMs. The current study, unfortunately, does not add improvements in our current knowledge. Thus, the authors need to evaluate carefully the current knowledge gap regarding EASM change and refine the scientific questions to be investigated.

References:

Xue, D., Lu, J., Leung, L.R. et al. Robust projection of East Asian summer monsoon rainfall based on dynamical modes of variability. Nat Commun 14, 3856 (2023). https://doi.org/10.1038/s41467-023-39460-y

Moon, S., Ha, KJ. Future changes in monsoon duration and precipitation using CMIP6. npj Clim Atmos Sci 3, 45 (2020). https://doi.org/10.1038/s41612-020-00151-w

Ha, K.‐J., Moon, S., Timmermann, A.,& Kim, D. (2020). Future changes of summer monsoon characteristics and evaporative demand over Asia in CMIP6 simulations. Geophysical Research Letters,47, e2020GL087492.https://doi.org/10.10