The paper describes a new macroscale hydrological model called CWatM. Although the model does not include much new functions compared with the most advanced similar models, but it does have several advantages due to its well organized code and adoption of modern technology. The unique feature of CWatM is that although global model, it can be easily applicable to specific basins. It also provides some tools for parameter tuning. These functions are seldom seen in earlier global models (exception is H08, Mateo et al. 2014; Masood et al. 2015). The text is well written and organized. The Section 5.4 and 5.5 are interesting, but too short to understand the methods and uncertainties in results.
Line 323-324 “With a simplification, the 1D Richards equation, is entirely gravity-driven and the matrix potential gradient is zero. This implies a flow that is always in a downward direction at a rate equal to the conductivity of the soil“: It sounds like that the authors assume the water transport in unsaturated zone is same as saturated one. Is this really the case?
Line 487 “Irrigation water demand”: Does CWatM consider multiple cropping? If so, how was it implemented?
Table 1: The original spatial resolution for DDM30 must be 30’.
Table 5 “Withdrawal of agricultural sector 2000 km3/yr:” I think the estimate is quite lower than that is shown in other reports. I am wondering this is partly due to the exclusion of multiple cropping.
Line 615 “Global calibration results”: During the calibration, were the models for human activities (e.g. water abstraction, reservoir operation, and others) enabled?
Line 640 “Section 5.4”: This section is very interesting, but too short to understand the methods and uncertainties in results. For instance, I hardly understood how the lake, the dam (the Owen Falls Dam), and water use in the study domain were treated. Are there any reports which include more detailed information?
Line 640 Section 5.5: Same as above. Are there any reports which include more detailed information?
Figure 7 the hydrograph for Matundo-Cais: It seems that the station is below the massive reservoir of Cahora Bassa. The observation in Fig 7 apparently shows the influence of reservoir operation (i.e. the seasonal fluctuation during low flow period is “unnaturally” stable). The simulated hydrograph also shows “unnatural” behavior which is quite different from the observation. Here comes my two questions. First, did the author consider the reservoir operation of Cahora Bassa in this study? If this is the case, how was the reproducibility of the dam operation (the dynamics of storage and release)?
Figure 8 I couldn’t understand how to understand the “violin diagram”. Elaborate what it shows.
Figure 8 Caption “at different values of a GHM”: Unclear. What does it mean?
Line 855 “Using CMIP6 datasets, (Eyring et al., 2016) is expected to reduce uncertainty”: The sentence seems incomplete.
Masood, M., Yeh, P. J. F., Hanasaki, N., and Takeuchi, K.: Model study of the impacts of future climate change on the hydrology of Ganges–Brahmaputra–Meghna basin, Hydrol. Earth Syst. Sci., 19, 747-770, 10.5194/hess-19-747-2015, 2015.
Mateo, C. M., Hanasaki, N., Komori, D., Tanaka, K., Kiguchi, M., Champathong, A., Sukhapunnaphan, T., Yamazaki, D., and Oki, T.: Assessing the impacts of reservoir operation to floodplain inundation by combining hydrological, reservoir management, and hydrodynamic models, Water Resources Research, 50, 7245-7266, 10.1002/2013wr014845, 2014.