the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 17 Apr 2025
Hillslope-Torrential Hazard Cascades in Tropical Mountains
Abstract. Torrential hazards refer to the spectrum of water-sediment flows that include debris flows, debris floods, hyperconcentrated flows, and flash floods. These processes often occur in cascading sequences with landslides and have been highly destructive in tropical and humid subtropical mountains, particularly. We compiled a database of 22 cascade events from 2009 to 2024 and analyzed topographic, sediment and the intensity and extremity of both antecedent and triggering rainfall to identify common traits of these events. The results showed that only a few cases were linked to the most extreme rainfall recorded, suggesting that other controls, such as sediment availability, may be needed for initiating hazard cascades. Clustering analysis revealed that regions with steeper slopes and finer soils experienced hazard cascades even under lower-intensity rainfall, whereas gentler slopes with coarser material required more extreme triggering rainfall. Cascades triggered by both earthquakes and rainfall showed that these triggers can interact across time, such as a rainy season preceding an earthquake or vice versa, or even simultaneously, highlighting the susceptibility of tectonically active tropical regions to cascading hazards. Our findings highlight the importance of prioritizing hazard assessment and risk reduction strategies in tropical mountains, especially in underreported areas such as Africa.
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RC1: 'Comment on egusphere-2025-1698', Anonymous Referee #1, 14 May 2025
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Dear Authors,
Your article represents a very important and interesting discussion. I suggest that it be published after minor revision. Below are some comments.The abstract is clearly and informatively written. The authors have provided basic information about torrential hazards, as well as the results obtained. One suggestion:
- At the end of the abstract, state the applicability of the study, i.e. to which institutions and organizations the obtained results will be useful.
At the beginning of the introduction, a major event is described, a natural disaster that caused great material and human losses.
-At the end of the introduction, you can add a few sentences about the following titles and subtitles.
-Subtitle 2.1. In Figure 1, you can add coordinates to fully show the geographical location.
The rest of the text is very well written. The relationship between topography, precipitation and lithology is explained in detail in different regions of the world. From the methodology to the conclusion, the authors have adequately conceptualized the text with accompanying cartographic and graphic content.
Citation: https://doi.org/10.5194/egusphere-2025-1698-RC1 -
RC2: 'Comment on egusphere-2025-1698', Anonymous Referee #2, 23 May 2025
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The work that concerns the formation of torrential hazard phenomena supplied by deposits of landslides is very interesting. Some comments as follows
The reviewer suggests the authors to give a look to the classification of torrential hazard provided by Brenna et al. (2020), Church and Jacob (2020), and Laigle and Bardou (2022).
About the debris flows that origin for entrainment of deposits from landslide or cliff failure into runoff, these are the case of Manival torrent in France (Theule, 2012) and Ru Secco torrent in Italy (Barbini et al., 2024). Barbini et al. (2024) also provides a schematic view of debris-flow triggering where debris flow can form when runoff entrain sediments from the deposits given by bank, slope and cliff failures.
Lines 94-96 “The resulting flow can be a debris flow or debris flood, or it can alternate between the two, for example when a channelized debris flow outpaces slower-moving flood waves of lesser sediment content; by bed erosion that causes flow bulking; or by an increase in discharge and sediment deposition of the debris flow” It could occur also an hyperconcentrated flow depending on the size of sediments and bed slope (Mark, 2017; Brenna et al., 2020; Laigle and Bardoux, 2022).
Line 200 authors should justify the choice of 90 days for the computing of the antecedent rainfall
Line 280 rainfall is estimated in mm: it should be mm/h or mm/day
Line 290 This result is very interesting
Lines 365-367 “However, CHIRPS estimated 25 mm on the event day. Similarly, for the 2020 Brazil event (16), CHIRPS estimated 11 mm on the event day, while Michel et al., (2021) reported 124 mm in a single day based on local rain gauge data. These inconsistencies were evident throughout the database, with absolute differences between reported and actual values decreasing as the accumulation period increased” Please note that Bernard and Gregoretti (2021) observed that changing the gauge used for the calibration, the radar estimates could highly vary.
The references Kaitna et al. (2024)a,b are the same.
References
Barbini, M., Bernard, M., Boreggio M., Schiavo, M., & Gregoretti C. (2024) An alternative approach for the sediment control of in-channel stony debris flows with an application to the case study of the Ru Secco Creek (Venetian Dolomites, Northeast Italy). Front. Earth Sci. - Geohazards and Georisks, 12, doi: 10.3389/feart.2024.1340561
Bernard, M. Gregoretti, C. (2021) The use of rain gauge measurements and radar data for the model-based prediction of runoff-generated debris-flow occurrence in early warning systems. Water Resources Research, 57(3), doi: 10.1029/2020WR027893
Brenna, A., Surian, N., Ghinassi, M., Marchi, L. Sediment–water flows in mountain streams: Recognition and classification based on field evidence, Geomorphology, 371, doi:10.1016/j.geomorph.2020.107413
Church, M., e Jacob, M. (2020) What Is a Debris Flood? Water Resources Research, 56(8), e2020WR027144
Laigle, D. Bardou, E. (2022) Mass-Movement Types and Processes: Flow-like mass movements, Debris Flows and Earth Flow In Treatise on Geomorphology, 2nd
Mark, E. (2017) Guidance for debris-flow and debris-flood mitigation design in Canada. Master’s Thesis, Simon Fraser University, 169 p.
Theule, J.I., Liebault, F., Loye, A., Laigle, D., and Jaboyedoff, M., 2012. Sediment budget monitoring of debris flow and bedload transport in the Manival Torrent, SE France. Natural Hazard Earth System Science 12, 371-749
Citation: https://doi.org/10.5194/egusphere-2025-1698-RC2
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