The authors (Ram et al. 2024) have utilized reprocessed data from NASA's web portal, for the period 2000–2020 (21 years) for six sites in Gujarat, India, to overcome the paucity of rainfall observations at those locations. They have generated dimensionless mass curves for monsoon rain at the locations (July–October), and compared these with the standard curves available in the literature (National Resource Conservation Service: NRCS 1986). The objective is praiseworthy, and more such studies are very much essential for India for developing a database of site-specific temporal distribution curves of rainfall. However, there are a few points that need clarification:

  • 1. Basin-scale curves for rainfall are already available for India (CWC-IMD-MoST 1992; IMD-CWC 2015, and similarly for other major river basins in India). The temporal distribution of rainfall represented in these curves is quite different from that of the NRCS curves. The deficiencies of the NRCS and other generic curves in representing site-specific temporal distribution of rainfall have already been highlighted for monsoon rainfall in India (Harshanth et al. 2021a, b), along with the possible reasons. The authors (Ram et al. 2024) missed out a recent article on generation of site-specific dimensionless mass curve for rainfall for a location (Tarapur, India) that is geographically close to the study area, wherein these curves were generated using observed rainfall data (Harshanth et al. 2023). The authors also missed out other articles which have attempted to address this issue for Indian monsoon sites (Dauji et al. 2021) employing other approaches. All these synthetic hyetographs that are available for India would have been more relevant for comparison, rather than the NRCS curves. The reason(s) for not considering the Indian curves for comparison remain unexplained.

  • 2. The fact remains that all the aforementioned curves pertain either to 24 h rainfall, or to individual storm rainfall. To the knowledge of this author, in the studies on development of dimensionless mass curves of rainfall in the literature (readers may refer to the references cited in Harshanth et al. 2023), temporal distribution curves of hourly rainfall have been used either over 24 h or in the duration of specific storm events. These have been averaged spatially (for basin-scale or generic), and temporally (for both site-specific and basin-scale) – to arrive at the desired dimensionless mass curve of rainfall. Departing from this approach, Ram et al. (2024) have used the daily rainfall data for the entire monsoon season to generate the cumulative mass curve (Figures 3 and 4: Ram et al. 2024); and from there, proceeded to derive the non-dimensional curves (Figures 5 and 6: Ram et al. 2024). Therefore, the rationale behind the comparison of the seasonal hyetograph (as derived by the Ram et al. 2024) with the generic hyetograph of 24 h rain (NRCS 1986) remains unclear.

  • 3. From the first principles, when a cumulative rainfall curve (rainfall vs time) of a storm is converted to a non-dimensional curve (non-dimensional rainfall vs non-dimensional time), the dimensionless rainfall reaches the value of unity simultaneously with the dimensionless time. This has been reflected in the dimensionless mass curves of rainfall reported in the literature (NRCS 1986; CWC-IMD-MoST 1992; IMD-CWC 2015; Harshanth et al. 2023 and references therein). In the synthetic seasonal hyetographs generated by the authors (Ram et al. 2024), it is possible that the dimensionless rainfall will reach the value of unity before the non-dimensional time reaches the value of unity. However, that would signify a dry spell towards the end of the monsoon season, and hence, there cannot be any non-dimensional rain after the value of unity has been reached once by the non-dimensional rain. It is needless to mention that the maximum value of cumulative non-dimensional rainfall (or time) can be unity.

  • The labels of the axes in Figure 7 of the article (Ram et al. 2024) are: ‘Elapsed Time (Dimensionless)’; and ‘Daily Rain (Dimensionless)’. The dimensionless rain reaches the value of unity in each of the six locations at different dimensionless times, and touches the value of unity twice for station Pilol (Figure 7(e)) – as dimensionless time proceeds from zero to unity. It is also apparent from Figure 7 that the cumulative rainfall derived from this figure would be much more than unity, for each of the six locations. This is in contrast with the information presented in Figures 5 and 6 of the article (Ram et al. 2024). How the curves presented in Figure 7 (Ram et al. 2024) were obtained from curves in Figures 5 and 6, or what they exactly portray, have not been explained. This is another aspect that needs resolution.

  • 4. In Figure 8, the authors (Ram et al. 2024) have compared the dimensionless curves of monsoon rainfall (developed by the authors) with the dimensionless curves for 24 h rainfall (NRCS 1986). The depiction of the dimensionless curves over two different time-resolutions/periods in the same plot would be scientifically valid only when the authors (Ram et al. 2024) can establish the fractal behavior of the rainfall, which they have not.

  • 5. In section ‘Materials and methods’ and sub-section ‘Deriving synthetic design hyetographs’, the authors (Ram et al. 2024) mentioned ‘hundreds of observed mass curves' were enveloped to generate the upper, middle, and lower design mass curves. However, according to the described methodology, and supported by the plots (Figures 3–6), it is understood that only 21 curves were available for each location. This aspect needs clarification.

    If the generic synthetic seasonal hyetographs were derived from only 21 curves for each location, this aspect needs to be highlighted as a limitation of the study. Basin-scale (CWC-IMD-MoST 1992; IMD-CWC 2015) or site-specific curves (Harshanth et al. 2023) reported for monsoon storms in India were each based on the analysis of many more curves than the acceptable value of 30 for statistical inferences.

All relevant data are included in the paper or its Supplementary Information.

The author declares there is no conflict.

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