土石流災害為坡地聚落安全之最大威脅，1996年賀伯颱風、2001年桃芝颱風及2009年莫拉克颱風等事件，均曾引發嚴重的土石流災害，為降低土石流災害之衝擊，目前對於土石流發生機制與土石流災害預警已有較深入的研究與建構完善的機制。但集水區在經歷高強度降雨衝擊或高震度地震影響後，於後續的降雨事件中，再次發生土石流災害的特性，尚未有深入之探討。因此本研究除分析土石流發生條件外，並著重分析土石流再發生之特性。本文蒐集1990~2024年間臺灣197條潛勢溪流270起土石流事件，依據陳天健等人(2015)的方法將土石流區分為坡面型及溪流型土石流兩大類，其中坡面型土石流75條91起事件，溪流型土石流122條179起事件。本研究分析這些土石流集水區之地文特性(集水區平均坡度、溪床坡度、形狀因子、險峻值、斷層及岩性)、觸發土石流的降雨特性(不同延時累積雨量、有效累積雨量與重現期)及集水區鬆散土砂變化(崩塌率及堆積土砂量)與土石流發生及再發生之關聯，並探討高強度地震及極端降雨事件對於引發土石流再次發生之影響。
分析結果顯示，溪流型土石流集水區土石流再發生可能性較坡面型土石流高，主要為溪床平均坡度較為平緩，利於土方積存河道成為下次發生之材料。統計坡面型土石流集水區再發生土石流比例約16%，且多發生在狹長型集水區；溪流型土石流集水區再發生土石流比例則為27%。集水區險峻值較大者，土石流再發生的可能性較高。坡面型土石流再次引發土石流需有較大有效累積雨量(需引發坡面發生新生崩塌)，溪流型土石流在較低有效累積雨量下便可能引發第2次災害(因坡面及河道內尚有前次事件之土砂積存)，結果說明土石流再次發生與集水區土砂生產及流出土砂量間有顯著相關性。
本研究結果亦指出，土石流事件發生後的第一年，集水區崩塌土砂料源供給充足，土石流再觸發雨量大部分比前次土石流事件低。此外，強震對土石流再發生的影響在於高強度地震會引發坡面大面積崩塌，若再遭遇較劇烈雨勢將會引發群發性土石流災害。地震前曾發生土石流的地區，地震後再發生土石流災害的可能性高。極端降雨(特別是12小時與24小時延時重現期達200年的降雨)易造成集水區地表沖蝕與崩塌，進而引發土石流再次發生。本研究也注意到有些土石流發生個案，雖然集水區水文及地文沒有顯著變化，但後續降雨卻再次觸發土石流，此反映出土石流再發生因素，除前述分析因子之外，仍具有其他的不確定因素，有待未來進一步探討。

Debris flows pose a significant hazard to hillside communities, as demonstrated by severe events during Typhoon Herb (1996), Typhoon Toraji (2001), and Typhoon Morakot (2009) in Taiwan. While considerable progress has been made in understanding debris flow mechanisms and developing early warning systems, the characteristics of debris flow reoccurrence particularly following high-intensity rainfall or seismic disturbances remain inadequately explored. This study investigates both the initial occurrence and reoccurrence of debris flows by analyzing 270 cases across 197 potential debris flow streams in Taiwan from 1990 to 2024. Following the classification by Chen et al. (2015), these events are categorized into hillslope-type debris flows (91 events in 75 streams) and channelized-type debris flows (179 events in 122 streams). Key factors examined include geomorphic characteristics (e.g., average catchment slope, channel gradient, shape factor, fault proximity, and lithology), rainfall metrics (e.g., accumulated and effective rainfall, return periods), and changes in loose sediment (e.g., landslide rate and deposition volume). The study further evaluates the influence of extreme rainfall and high-magnitude earthquakes on debris flow reoccurrence.
Results indicate that channelized-type debris-flow catchments exhibit a higher likelihood of debris flow recurrence (27%) compared to slope-type debris-flow catchments (16%), primarily due to gentler channel slopes that facilitate sediment accumulation. Hillslope-type debris flows tend to recur in elongated catchments and require higher effective rainfall. In contrast, channelized -type debris flows may be triggered by lower effective accumulated rainfall, as debris from the previous event may still remain on hillslopes and channel. These results demonstrate a significant relationship between debris-flow reoccurrence and both sediment production and sediment yield from the catchment.
Abundant landslide-derived sediment supply typically persists in the catchment during the first year following a debris-flow event, resulting in lower rainfall thresholds for subsequent debris-flow initiation compared to the previous event. High-magnitude earthquakes are known to generate extensive slope failures, and when followed by intense rainfall, such conditions can induce clustered debris-flow disasters. Areas that experienced debris flows prior to an earthquake therefore exhibit a higher likelihood of recurrence afterward. Moreover, extreme rainfall events—particularly 12-hour and 24-hour durations with return periods of 200 years—are capable of triggering slope erosion and severe failure, subsequently leading to renewed debris-flow activity. Notably, some debris flows have been reactivated even in catchments where no significant hydrological or geomorphological changes were observed, suggesting the presence of additional uncertain factors beyond those analyzed in this study. These unknown influences warrant further investigation.

1.Baum, R.L., Godt, J.W., and Savage, W.Z., “Estimating the timing and location of shallow rainfall-induced landslides using a model for transient, unsaturated infiltration”, J. Geophys. Res.-Earth, 115, F03013. doi:10.1029/2009JF001321. (2010)
2.Caine, N., “The Rainfall Intensity Duration Control of Shallow Landslides and Debris Flows”, Geografiska Annaler, 62, 23-27. (1980).
3.Cannon S.H., Degraff J., “The Increasing Wildfire and Post-Fire Debris-Flow Threat in Western USA, and Implications for Consequences of Climate Change”, Landslides – Disaster Risk Reduction, 177-190. (2009)
4.Cannon S., Gartner J., Wilson R., Bowers J., Laber J., “Storm rainfall conditions for floods and debris flows from recently burned areas in southwestern Colorado and southern California”, Geomorphology , 96, 250–269. (2008)
5.Chang C.W., Lin P.S., Tsai C.L., “Estimation of sediment volume of debris flow caused by extreme rainfall in Taiwan”, Engineering Geology, 123, 83–90. doi:10.1016/j.enggeo.2011.07.004. (2011)
6.Chen C.Y., Wang Q. “Debris flow-induced topographic changes: effects of recurrent debris flow initiation”, Environ Monit Assess, 189 (449). DOI 10.1007/s10661-017-6169-y. (2017)
7.Chen H.W., Chen C.Y., “Warning Models for Landslide and Channelized Debris Flow under Climate Change Conditions in Taiwan”, Water, 14, 695. https://doi.org/10.3390/w14050695 (2022).
8.Chen J.C., Huang W.S., “Evaluation of Rainfall-Triggered Debris Flows under the Impact of Extreme Events: A Chenyulan Watershed Case Study, Taiwan”, Water, 13, 2201. https://doi.org/10.3390/w13162201 (2021)
9.Chen J.C., Huang W.S., Tsai Y.F., “Variability in the characteristics of extreme rainfall events triggering debris flows: a case study in the Chenyulan watershed, Taiwan”, Natural Hazards ,102, 887–908. https://doi.org/10.1007/s11069-020-03938-5. (2020)
10.Chen J.C., “Variability of impact of earthquake on debris-flow triggering conditions: case study of Chen-Yu-Lan watershed, Taiwan”, Environ Earth Sci, 64:1787–1794. DOI 10.1007/s12665-011-0981-4. (2011)
11.Chen C.W., Saito H., Oguchi T., “Rainfall intensity–duration conditions for mass movements in Taiwan”, Progress in Earth and Planetary Science, 2:14. DOI 10.1186/s40645-015-0049-2. (2015)
12.Chen X. L., Yu L., Wang M.M., Lin C. X., Liu C.G., Li J.Y., “Brief Communication: Landslides triggered by the Ms =7.0 Lushan earthquake”, China, Nat. Hazards Earth Syst. Sci., 14, 1257–1267. doi:10.5194/nhess-14-1257-2014. (2014)
13.Chen Y.C., Chang K.T., Chiu Y.J., Lau S.M., Lee H.Y., “Quantifying rainfall controls on catchment-scale landslide erosion in Taiwan”, Earth Surf. Process. Landforms, 38, 372–382. DOI: 10.1002/esp.3284 (2013).
14.Chen N.S., Hu G.S., Deng M.F., Zhou W., Yang C.L., Han D., Deng J.H., “Impact of earthquake on debris flows - a case study on the wenchuan earthquake”, Journal of Earthquake and Tsunami, 5(5), 493–508. DOI: 10.1142/S1793431111001212. (2011)
15.Glade T., Crozier M., Smith P., “Applying probability determination to refine landslide-triggering rainfall thresholds using an empirical “Antecedent Daily Rainfall Model”, Pure and Applied Geophysics, 157, 1059–1079. (2000)
16.Guzzetti, F., Peruccacci, S., Rossi, M., and Stark, C.P., “The rainfall intensity-duration control of shallow landslides and debris flow”, Landslides, 5 (1), 3–17. (2008).
17.Guzzetti F., Peruccacci S., Rossi M., Stark C.P., “The rainfall intensity-duration control of shallow landslides and debris flows: an update”, Landslides, 5, 3–17. DOI 10.1007/s10346-007-0112-1. (2007)
18.Guzzetti F., Reichenbach P., Cardinali M., Galli M., Ardizzone F., “Probabilistic landslide hazard assessment at the basin scale”, Geomorphology, 72, 272–299. (2005)
19.Huang Y.M., “Characteristics of debris flows recorded in the Shenmu area of central Taiwan between 2004 and 2021”, Nat. Hazards Earth Syst. Sci., 23, 2649–2662. https://doi.org/10.5194/nhess-23-2649-2023. (2023)
20.Iverson R.M., “Landslide triggering by rain infiltration”, Water Resour Res, 36(7),1897–1910. https://doi.org/10.1029/2000WR900090 (2000).
21.Jan C.D., Wang J.S., Zeng Y.C., Kuo F.H., “Early Warning Criteria for Debris flows and their application in Taiwan”, Landslide Dynamics: ISDR-ICL Landslide, Interactive Teaching Tools, https://doi.org/10.1007/978-3-319-57774-6_30 (2018).
22.Jan C.D., Lee M.H., Wang J.S., & Wang C.L., “A rainfall-based debris-flow warning model and its application in Taiwan”, International Conference on Slope Disaster Mitigation Strategy, 111-119. (2004).
23.Keefer, D.K. et al, “Real time landslide warming during heavy rainfall”, Science, Vol. 238, 99. 921-925. (1987)
24.Kim S.W., Chun K.W., Otsuki K., Shinohara Y., Kim M.I., Kim M.S., Lee D.K., Seo J.I., Choi B.K., “Heavy Rain Types for Triggering Shallow Landslides in South Korea”, J. Fac. Agr., Kyushu Univ., 60 (1), 243–249. https://www.researchgate.net/publication /282179943 (2015).
25.Lin C.W., Shieh C.L., Yuand B.D., Shiehb Y.C., Liu S.H., Lee S.Y., “Impact of Chi-Chi earthquake on the occurrence of landslides and debris flows: example from the Chenyulan River watershed, Nantou, Taiwan”, Engineering Geology, 71, 49–61. (2003)
26.Lin C.W., Liu S.H., Lee S.Y., Liu C.C., “Impacts of the Chi-Chi earthquake on subsequent rainfall-induced landslides in central Taiwan”, Engineering Geology, 86, 87–101. doi:10.1016/j.enggeo.2006.02.010. (2006)
27.Meunier P., Hovius N., Haines A.J., “Regional patterns of earthquake-triggered landslides and their relation to the ground motion”, Geophysical Research Letters, 34, L20408. doi:10.1029/2007GL031337. (2007)
28.Melton, M.A., “The Geomorphic and Palaeoclimatic Significance of Alluvial Deposits in Southern Arizona”, Journal of Geology, 73, 1-38. (1965)
29.Nettleton, I.M., Martin, S., Hencher, S., and Moore, R., “Debris flow types and mechanisms”, In M.G. Winter ,F. Macgregor and L, Sahckman (Eds) Scottish Road Network Landslides Study, 45-67. Edinburgh: The Scottish Executive. (2005)
30.Okada K, Makihara Y, Shimpo A, Nagata K, Kunitsugu M, Saito K., “Soil Water Index, Tenki”, 48, 349–356. (2001) (in Japanese)
31.Papa M.N., Medina V., Ciervo F., Bateman A., “Derivation of critical rainfall thresholds for shallow landslides as a tool for debris flow early warning systems”, Hydrol. Earth Syst. Sci., 17, 4095–4107. doi:10.5194/hess-17-4095-2013. (2013)
32.Song C., Yu C., Li Z., Utili S., Frattini P., Crosta G., Peng J., “Triggering and recovery of earthquake accelerated landslides in Central Italy revealed by satellite radar observations”, Nature communications. https://doi.org/10.1038/s41467-022-35035-5. (2022)
33.Staley D.M., Kean J.W., Rengers F.K., “The recurrence interval of post-fire debris-flow generating rainfall in the southwestern United States”, Geomorphology, 370, 107392. https://doi.org/10.1016/j.geomorph.2020.107392. (2020)
34.Tanyaş H., Kirschbaum D., Görümd T., Westen C.J.V., Tang C, Lombardo L., “A closer look at factors governing landslide recovery time in post-seismic periods”, Geomorphology, 391, 107912. https://doi.org/10.1016/j.geomorph.2021.107912. (2021)
35.Takahashi T., “Debris flow mechanics, prediction and countermeasures”, published by Taylor & Francis. (2007)
36.Tiwari B., Ajmera B., “Landslides Triggered by Earthquakes from 1920 to 2015”, 4th World landslide forum. (2017)
37.Wilford, D.J., Sakals, M.E., Innes, J.L., Sidle, R.C., Bergerud, W.A., “Recognition of debris flow, debris flood and flood hazardthrough watershed morphometrics”, Landslides, 1, 61–66. (2004)
38.Yuan R.M., Deng Q.H., Cunningham D., Xu C., Xu X.W., Chang C.P., “Density Distribution of Landslides Triggered by the 2008 Wenchuan Earthquake and their Relationships to Peak Ground Acceleration”, Bulletin of the Seismological Society of America, 103(4), 2344–2355. doi: 10.1785/0120110233. (2013)
39.Zhang S., Peng J.Y., Zhang M.P., Chen Y.B., Han Y.Y., Su C.X., Zhuang D.Y., “Evolution of debris flow activities in the epicentral area, 10 years after the 2008 Wenchuan earthquake”, Engineering Geology, 319, 107118.
https://doi.org/10.1016/j.enggeo.2023.107118. (2023)
40.Zhang S., Zhang L.M., Chen H.X., “Relationships among three repeated large-scale debris flows at Pubugou Ravine in the Wenchuan earthquake zone”, Can. Geotech. J. 51, 951–965. dx.doi.org/10.1139/cgj-2013-0368. (2014)
41.Zhou, W., Tang, C., Van Asch, T. W., Chang, M., “A rapid method to identify the potential of debris flow development induced by rainfall in the catchments of the Wenchuan earthquake area. Landslides”, 13(5), 1243-1259. (2016)
42.沈哲緯、蕭震洋、羅文俊，花蓮縣土石流潛勢溪流地文特性初探，水保技術,，7(2)，96-105。 (2012)
43.李宁、唐川、卜祥航、李浩宾，512地震后汶川县泥石流特征与演化分析，工程地质学报，28(6)，1233-1245。doi:10.13544/j.cnki.jeg.2019-31。(2020)
44.林裕益、何世華、周文杰，國道路廊對沿線集水區地表逕流影響之研究，中華水土保持學報，40(4)，467-479. (2008)
45.林昭遠、張力仁，地文因子對土石流發生影響之研究-以陳有蘭溪為例，中華水土保持學報，31(3)，227-237. (2000)
46.成功大學防災研究中心，桃芝颱風風災區土石流災害潛勢分析，行政院農業委員會水土保持局委託計畫成果報告書。 (2001)
47.吳輝龍；陳文福、張維訓，集水區地文特性因子與土石流發生機率間相關性之研究-以陳有蘭溪為例，中華水土保持學報，35(3)，251-259。http://dx.doi.org/10.29417/JCSWC.200409_35(3).0006。(2004)
48.周憲德，堆積扇地貌特性與土砂災害類型之探討，農委會水土保持局創新研究計畫報告。(2020)
49.周憲德、廖偉民，孔隙水壓對溪床土石流發生機制之影響，中華水土保持學刊，29(3)，211-217。(1998)
50.范正成、劉哲欣、吳明峰，南投地區土石流發生臨界降雨線之設定及其於集集大地震後之修正，中華水土保持學報，33(1)，31-38。(2002)
51.倪化勇，基于地貌特征的泥石流类型划分，南水北调与水利科技，13(1)，78-82。DOI:10.13476/j.cnki.nsbdqk.2015.01.018。(2015)
52.陳天健、陳思妤，基於坡面型土石流潛能之溪流型土石流潛勢評估模式-板岩地區，中華水土保持學報，50(3)，89-101。DOI: 10.29417/JCSWC.201909_50(3).0001。(2019)
53.陳天健、羅元勳、楊婉君、陳柏龍，坡面型土石流地行判釋分析模式，中華水土保持學報，47(2)，95-103。(2016)
54.陳天健、王振宇、陳柏龍，坡面型土石流之地形特徵與判別方法，中華水土保持學報，46(3)，133-141。(2015)
55.陳文福，李毅宏，吳輝龍，結合地文與降雨條件以判定土石流發生之研究-以陳有蘭溪集水區為例，台灣地理資訊學刊，1(2)，27-44。 (2005)
56.陳文福，集水區地文因子與土石流發生相關性之研究，農業委員會水土保持局專題研究報告。(2003)
57.陳晉琪，土石流發生條件及發生機率之研究，成功大學水利及海洋工程系博士論文。(2000)
58.曾奕超、詹錢登，溪流型與坡面型土石流發生及再發生特性之研究，中華防災學刊，17(1)，9-22。(2025)
59.曾奕超，土石流發生降雨地文綜合警戒指標之研究，成功大學水利及海洋工程系碩士論文。(2003)
60.詹錢登，土石流防災降雨警戒，財團法人中興工程科技研究發展基金會。（2016）
61.詹錢登、李明憙，土石流發生降雨警戒模式，中華水土保持學報，35(3)，275-285。(2004)
62.詹錢登，土石流發生降雨警戒值模式之研究，行政院農委會水土保持局科技計畫。 (2002)
63.詹錢登，土石流概論，科技圖書股份有限公司。（2000）
64.農業部農村發展及水土保持署，土石流及大規模崩塌防災資訊網，重大災害事件，Website : https://246.ardswc.gov.tw/Achievement/MajorDisasters。(2025)
65.農業部農村發展及水土保持署，巨量空間資訊系統(BIGGIS)。
Website : https://gis.ardswc.gov.tw/。 (2025)
66.謝正倫、陸源忠、游保杉、陳禮仁，(1995)，「土石流發生臨界降雨線設定方法之研究」，中華水土保持學報，26(3)，167-172。(Shieh C.L., Luh Y.C., Yu P.S., and Chen L.J. (1995)