I appreciate the effort of authors in developing this interesting field. However, the assumptions of the proposed method are in my opinion incorrect:

1. Hydrograph components, i.e. the event and pre-event water, do not represent young and old water fractions defined by the young water fraction concept.
2. The conceptual problem in my opinion is that if the young water fraction is defined as a characteristic (metric) calculated from the seasonal variability of a tracer, it is attributed to the seasonal time scale. Thus, it is not meaningful to “improve” the temporal resolution of such a characteristic for finer scales (hydrographs) if the tracer streamflow data is sparse.
3. EC is not a conservative tracer although it is generally true that the longer the water stays in the catchment, the more ions it contains. However, EC varies also with air (water) temperature despite temperature compensation employed in the sensors and if an event water meets very soluble minerals, it can have high EC as well.
4. Exponential relationship between EC and discharge (increasing event water contribution) appears when the long-term data (combining many events) is analysed. However, measurements I have seen did not document such a relationship for individual runoff events (hydrographs). While generally the EC does decrease with increasing discharge for many events, it does not happen so for each event. In fact, in my experience a decrease in EC with increase in discharge was evident only during larger events. Thus, it is in my opinion incorrect to apply the general relationship emerging from the long-term data for all individual events.
5. I agree that catchments with a greater number of runoff events (i. e. more frequent higher discharge) likely have higher young water fraction. Therefore, I appreciate the idea of calibrating separated event/pre-event water components for all the events of period used to determine the young water fractions to estimate the proportion of “young water fractions” (see comment 2) in individual events. However, as I argue above, the EC does not provide the reliable information. Furthermore, I think that isotopes (atoms of elements forming water) and  EC (ions of compounds saluted in water) may not provide the same (compatible) information about the streamwater sources. Last but not least, catchment runoff response is nonlinear. It is therefore questionable to assume that the young water fractions of individual events are proportional to distribution of the event water fractions.

I regret to conclude that, based on the above, I cannot recommend the manuscript for publication.

This article presents an interesting method for estimating the young water fraction based on high-resolution EC measurements. My only two major concerns are: 1) the authors may consider providing more evidence or referencing literature to support their three main assumptions for the method; and 2) the authors could discuss how their method can be applied to other basins beyond their experimental watersheds. I also have some smaller comments as follows:

1. Lines 52-55, readers may seek more detailed descriptions for the terms 'unweighted,' 'flow-weighted,' and 'time-weighted.'

2. Lines 85-86, what do you mean by the 'uncertainty of the discharge sensitivity of the young water fraction'?

3. Table 2, are the numbers of 18O samples and EC samples the same?

4. Eqs. 2.1-2.2, I would appreciate more details on the estimation of As, A*s and Ap.

5. Figure 5, could you explain what Qmed and Q50/50 represent?

6. Figure 6, is the variable snow depth represented as HS in the figure? Please specify the years in each of the panels.

7. Figure 7, why not include a scatter plot for Fyw and P, which might better illustrate the correlation?

8. Line 395, 'significantly reduced the uncertainty of'—how can we observe this reduction in uncertainty from the results section? Please provide more details in the text.