Comments on "Technical note: An innovative monitoring approach to measure spatio-temporal throughfall patterns in forests" submitted to HESS-D by Lea Dedden & Markus Weiler.

[General comment]

This paper proposed monitoring system for throughfall with tipping bucket instrument, which authors had developed recently (Paulsen and Weiler, 2025). I agree that spatial distribution of throughfall is highly heterogeneous, and interception studies require instruments which can measure the spatial distribution of throughfall easily and validly. So, I could understand authors' motivations shown in this paper, but I regret to say that this paper should be rewritten very carefully.

  When tipping bucket system is applied to measure inflow of water, static and dynamic calibrations are necessary, as authors cited Shimizu et al. (2018). Authors did very careful calibration of static volume of one tip. Also, increasing underestimation of one tip for increasing inflow must be considered. The static one tip volume is 2.21 to 3.69 mL, ranging 0.037 mm to 0.062 mm, relatively high resolution for gross rainfall and throughfall measurement. Please note that underestimation occurs at every tip under high intensity, and number of tips should increase with higher resolution (smaller volume of one tip), leading to larger underestimation compared with tipping bucket of low resolution (larger volume). As authors stated, throughfall sometimes exceeds gross rainfall, strongly requiring applying correction based on the dynamic calibration. This is "technical note", in which well-known uncertainties must be evaluated carefully. The one tip volume is similar with Onset and Davis rain gauges, and their dynamic calibration curve had been described in Iida et al. (2012, Hydrological Processes) and Iida et al. (2018, Journal of Hydrometeorology).

  Title of this paper is "... to measure spatio-temporal throughfall patterns in forests". However, reading the current manuscript, main results are rainwater passing through the litter manually put on the capturing area. Changing logic through the manuscript is not suitable for scientific journals. Please confirm that the current objectives (line 111-114) include throughfall only. If authors want to focus on rainwater passing through the litter, careful revisions must be required for whole manuscript.

  I feel strange for expression of "infiltration" measured by this equipment. The tipping bucket measures inflow of rainwater, which passed the litter put on the capturing area of throughfall. I could not think that the inflow is the same as infiltration into soil. To declare infiltration, at least, initial soil water condition, inflow intensity, infiltration capacity and topography (slope or flat) should be considered.

[Specific comments]

Line 7-21 (abstract)

There is no "infiltration" among these lines. Readers could not expect that this paper describes inflow of rainwater passed through the litter put on the capturing area.

Line 25-85

Detailed background for interception process including throughfall measurement is written here, but these topics are not investigated in this manuscript. I agree that sample size is important issue for throughfall studies, but I could not understand how this equipment contributes to this issue.

Line 192-212

It is somewhat difficult for me to understand the situation. Is it correct that newly developed instruments here were used for only measurement of rainwater inflow passing litter? Troughs collect throughfall, but are these data shown in this MS? If trough data is not used, related sentences must be removed. Rainwater captured by trough was measured by Davis rain gauge, so actual one tip should be very small. Please note that underestimation by Davis gauge is high (Iida et al., 2018), and careful attention should be paid for measurements.

Line 245-294, 295-351

These results are "infiltration", that is rainwater inflow passed the litter. However, in discussion section, results are compared with previous throughfall studies. Readers should feel strange. In my opinion, as this equipment is throughfall measurement system, authors should compare the throughfall measurements by this new system and the ordinary gauges like storage type point gauges. That is very simple and clear way to show the validity of new system.

Line 353-357

These are well-known uncertainties for tipping bucket, which should be considered carefully in this manuscript.

Line 370

Not all readers know ECOSENSE. Please take care of readers.

[Technical corrections]

Line 166

Please check [ tips" ].