Reply on CC1

Include the findings from Sections 3.6 and 3.7 in the abstract. Response: We have re-written the abstract to include these findings. Line 432: Typo “featured emerged” replace with “features emerged” Response: Typo fixed. Lines 449-450: I did not see a section on calibration of GFS using IMERG-Early. Please clarify or remove this sentence Response: We have removed this sentence. Please also note the supplement to this comment: https://hess.copernicus.org/preprints/hess-2021-250/hess-2021-250-AC3-supplement.pdf Powered by TCPDF (www.tcpdf.org)

averaging spatial scale, and rainfall rate.
2) Abstract: Last sentence: It is not clear whether the authors performed an analysis to support this statement. If yes, this statement should be supported with the method and findings utilized, otherwise it is a general statement and should be removed from abstract.

Response:
We agree that we have not provided supporting analysis, and therefore have replaced the statement "The accuracy of GFS forecasts could be improved by applying post-processing techniques involving near-real time satellite rainfall products." with "We recommend exploring appropriate post-processing calibration techniques, that use nearreal time products, such as, IMERG Early, to improve the performance of GFS, particularly at shorter time scales." The reason for our recommendation is that IMERG Early outperforms GFS in most cases, and therefore, it can be used to calibrate GFS. The IMERG Early outperform GFS in Wet Guinea and Savannah regions in terms of bias, and the spatial structure of IMERG Early is the same as IMERG Final -as the main difference between the two products in the inclusion or exclusion of rain gauge data which affects primarily the bias. However, it is not clear what kind of post-processing technique is more appropriate.
3) I think Section 2.Data and Methodology should be divided into two sections namely "2. Study Area and Datasets" and "3. Methodology". Lines 141-196 should move to the 2.1. Study Area section. Current Sections 2.1-2.3 should move to new "2.2. Datasets" section. Current Section 2.4 should move to "3.Methodology" section. This section should also include other data processing methods used in the study such as scale matching between products, basin-scale conversion etc. as well as study time period.

Response:
We have re-arranged the sections as follows. We have created a separate section labeled "Study Region" and moved Lines 141 -196 to the Study Region section. In the 'Evaluation' Section, we have added the data processing methods. Figure 3 and shown in Figure 4 but not discussed in text. The reader has no information about this product until Section 3.5. To eliminate this confusion, please discuss the motivation for producing this rainfall dataset and the methodology for adjusting IMERG Early using IMERG Final in the Methodology section (Lines 347-352 in the manuscript). It may be worthwhile to indicate that the advantage of simple climatological correction for IMERG Early would be the shorter lag time (a few hours) compared to IMERG Final (3.5 months).

Response:
We have decided to remove the 'IMERG Early Cal' dataset from our evaluation (as also suggested by another Reviewer). The climatological bias correction approach used to generate the 'IMERG Early Cal' dataset did not really improve performance compared to IMERG Early. 5) Section 3.4: This section shows the scatterplots comparing correspondence between daily rainfall events between IMERG Final and GFS. Therefore, it is not related to uncertainty but a different way of comparing daily events. Section 3.4 can therefore be merged with Section 3.3.

Response:
Yes, however, we formed our different sections based on the different ways of comparisons. 6) Section: 3.6: Please discuss the methodology for changing spatial scale of the products in the Methodology section. Moreover, indicate the reference rainfall product used in this section (IMERG Final). It may be helpful for the reader to include the watershed area next to each watershed name in Figure 9. Also somewhere in the manuscript, the number of rainfall product grids over each dam watershed should be provided.

Response:
We have included the methodology in the 'Evaluation' Section. We have added the watershed areas. 7) I suggest that the title of the manuscript should be modified to include the use of satellite rainfall products in the comparison. For example something similar to "Performance evaluation of the Global Forecast System's Medium-Range Precipitation Forecasts in the Niger River Basin using multiple satellite-based products." Response: Yes, this is a better title. We have used it. 8) In conclusion section, a discussion on the study findings for dam operation would be beneficial for the reader since the focus is on dam watersheds (for example the impact of change in lead time performance in dam operation).
Response: Yes, this is an important issue. However, it is difficult for us to state the implication of the forecast accuracy on reservoir operation at this stage, simply because the relationship between forecast accuracy and dam operation is not well-known. This could be a good topic for future research -thank you for the idea.