NHESS Natural Hazards and Earth System Sciences NHESS Nat. Hazards Earth Syst. Sci. 1684-9981 Copernicus Publications Göttingen, Germany 10.5194/nhess-10-571-2010 Recent changes in rainfall characteristics and their influence on thresholds for debris flow triggering in the Dolomitic area of Cortina d'Ampezzo, north-eastern Italian Alps Floris M. 1 D'Alpaos A. 1 Squarzoni C. 1 Genevois R. 1 Marani M. 2 Department of Geosciences, University of Padova, Padova, Italy Department IMAGE, University of Padova, Padova, Italy 26 03 2010 10 3 571 580 Copyright: © 2010 M. Floris et al. 2010 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://nhess.copernicus.org/articles/10/571/2010/nhess-10-571-2010.html The full text article is available as a PDF file from https://nhess.copernicus.org/articles/10/571/2010/nhess-10-571-2010.pdf

In this paper, we examine variations in climate characteristics near the area of Cortina d'Ampezzo (Dolomites, Eastern Italian Alps), with particular reference to the possible implications for debris-flow occurrence. The study area is prone to debris-flow release in response to summer high-intensity short-duration rainfalls and, therefore, it is of the utmost importance to investigate the potential increase in debris-flow triggering rainfall events. The critical rainfall threshold is agreed to be a crucial triggering factor for debris-flows. Data from a monitoring system, placed in a catchment near Cortina (Acquabona), show that debris-flows were triggered by rainfalls with peak rainfall intensities ranging from 4.9 to 17.4 mm/10 min. <br><br> The analyses of meteorological data, collected from 1921 to 1994 at several stations in the study area, show a negative trend of annual rainfall, a considerable variation in the monthly rainfall distribution, and an increase in the temperature range, possibly related to global climate changes. Moreover, high-intensity and short-duration rainfall events, derived from data collected from 1990 and 2008, show an increase in exceptional rainfall events. The results obtained in a peak-over-threshold framework, applied to the rainfall data measured at the Faloria rain gauge station from 1990 to 2008, clearly show that the interarrival time of over-threshold events computed for different threshold values decreased in the last decade. This suggests that local climatic changes might produce an increase in the frequency of rainfall events, potentially triggering debris flows in the study area.

 References Berti, M., Genevois, R., Simoni, A., and Tecca, P. R.: Field observations of a debris flow event in the dolomites, Geomorphology, 29, 265–274, 1999. Berti, M., Genevois, R., LaHusen, R., Simoni, A., and Tecca, P. R.: Debris flow monitoring in the Acquabona watershed (Dolomites, Italian Alps), Phys. Chem. Earth Pt.&nbsp;B., 25(9), 707–715, 2000. Blijenberg, H. M.: Rolling Stones? Triggering and frequency of hill slope debris flows in the Bachelard Valley, Southern French Alps, Ph.D.&nbsp;thesis, Utrecht University, 233&nbsp;pp., 1998. Caine, N.: The rainfall intensity-during control of shallow landslides and debris flows, Geogr. Ann.&nbsp;A, 62, 23–27, 1980. Cannon, S. H., Gartner, J. E., Rupert, M. G., Michael, J. A., Djokic, D., and Sreedhar, S.: Emergency Assessment of Debris-Flow Hazards from Basins Burned by the Grand Prix and Old Fires of 2003, Southern California, USGS, Open-File Report, 03-0475, 2003. Chen, C. Y., Chen, T. C., Yu, F. C., Yu, W. H., and Tseng, C. C.: Rainfall duration and debris-flow initiated studies for real-time monitoring, Environ. Geol., 47, 715–724, 2005. Chen, C. Y., Yu, F. C., Lin, S. C., and Cheung, K. W.: Discussion of landslide self-organized criticality and the initiation of debris flow, Earth Surf. Proc. Land., 32(2), 197–209, 2006. Coe, J. A., Godt, J. W., Parise, M., and Moscariello, A.: Estimating debris-flow probability using fan stratigraphy, historic records, and drainage-basin morphology, Interstate 70 highway corridor, central Colorado, U.S.A., in: Debris-Flow Hazards Mitigation: Mechanics, Prediction, and Assessment, edited by: Rickenmann, D. and Cheng, Ch., Proceedings 3rd International DFHM Conference, Davos, Switzerland, 207–217, 2003. Coe, J. A., Cannon, S. H., and Santi, P. M.: Introduction to the special issue on debris flows initiated by runoff, erosion, and sediment entrainment in western North America, Geomorphology, 96, 247–249, 2008a. Coe, J. A., Kinner, D. A., and Godt, J. W.: Initiation conditions for debris flows generated by runoff at Chalk Cliffs, central Colorado, Geomorphology, 96, 270–297, 2008b. Easterling, D. R., Evans, J. L., Groisman, P. Y., Karl, T. R., Kunkel, K. E., and Ambenje, P.: Observed variability and trends in extreme climate events: a brief review, B. Am. Meteorol. Soc., 81, 417–425, 2000. Evans, S. G. and Clague, J. J.: Recent climatic change and catastrophic geomorphic processes in mountain environments, Geomorphology, 10, 107–128, 1994. Eybergen, F. A. and Imeson, A. C.: Geomorphic processes and climatic change, Catena, 16, 307–319, 1989. Fauchereau, N., Trzaska, S., Rouault, M., and Richard, Y.: Rainfall variability and changes in Southern Africa during the 20th century in the global warming context, Nat. Hazards, 29, 139–154, 2003. Fowler, H. J. and Kilsby, C. G.: Implications of changes in seasonal and annual extreme rainfall, Geophys. Res. Lett., 30(13), 1720, https://doi.org/10.1029/2003GL017327, 2003. Fowler, H. J., Ekström, M., Kilsby, C. G., and Jones, P. D.: New estimates of future changes in extreme rainfall across the UK using regional climate model integrations. 1. Assessment of control climate, J. Hydrol., 300, 212–233, 2005. Galgaro, A., Tecca, P. R., Genevois, R., and Deganutti, A. M.: Acoustic module of the Acquabona (Italy) debris flow monitoring system, Nat. Hazards Earth Syst. Sci., 5, 211–215, 2005. Genevois, R., Tecca, P. R., Berti, M., and Simoni, A.: Pore pressure distribution in the initiation area of a granular debris flow, in: Proceedings of the 8th International Symposium on Landslides, edited by: Bromhead, E., Dixon, N., and Ibsen, M. L., Cardiff, 12, 615–620, 2000. Genevois, R., Tecca, P. R., Deganutti, A. M., Galgaro, A., and Armento, C.: Scientific Contributions. European Project Torrent Hazard Control in the European Alps. Practical Tools and methodologies for Hazard Assessment and Risk Mitigation, Contract no. EVG1-CT1999-00012, Final Report, 67&nbsp;pp., 2003. Gong, D. Y. and Wang, S. W.: Severe summer rainfall in China associated with enhanced global warming, Clim. Res., 16, 51–59, 2000. Griffiths, P. G., Webb, R. H., and Melis, T. S.: Initiation of debris flows in tributaries of the Colorado River in Grand Canyon, Arizona. In: C.L. Chen, Editor, Debris-flow Hazards Mitigation, American Society of Civil Engineers, New York, 12–20, 1997. Haeberli, W., Rickenmann, D., and Zimmerman, M.: Investigation of 1987 debris flows in the Swiss Alps: general concept and geophysical soundings, in: Hydrology in Mountainous regions. II Artificial reservoirs; Water and slopes, Proceedings of two Lausanne Symposia, IAHS, 194, 303–310, 1990. Jomelli, V., Brunstein, D., Grancher, D., and Pech, P.: Is the response of hill slope debris flows to recent climate change univocal? A case study in the Massif des Ecrins (French Alps), Climatic Change, 85, 119–137, 2007. Keefer, D. K., Wilson, R. C., Mark, R. K., Brabb, E. E., Brown III, W. M., Ellen, S. D., Harp, E. L., Wieczorek, G. F., Alger, C. S., and Zatkin, R. S.: Real-time landslide warming during heavy rainfall, Science, 238, 921–925, 1987. Mann, H. B. and Whitney, D. R.: On a test of whether one of two random variables is stochastically larger than the other, Ann. Math. Stat., 18, 50–60, 1947. Monirul Qader Mirza, M.: Global warming and changes in the probability of occurrence of floods in Bangladesh and implications, Global Environ. Chang., 12, 127–138, 2002. Pelfini, M. and Santilli, M.: Frequency of debris flows and their relation with precipitation: A case study in the Central Alps, Italy, Geomorphology, 101, 721–730, 2008. Rickenmann, D. and Zimmermann, M.: The 1987 debris flow in Switzerland: documentation and analysis, Geomorphology, 8, 175–189, 1993. Shieh, C. L. and Chen, L. Z.: Developing the critical line of debris-flow occurrence. Journal of Chinese Soil and Water Conservation, 26(3), 167–172, 1995 (in Chinese). Shieh, C. L.: Debris flow surveillance in central Taiwan after Typhoon Toraji, Disaster Prevention Research Center, National Cheng-Kung University, 2002 (in Chinese). Shieh, C. L., Chen, Y. S., Tsai, Y. J., and Wu, J. H.: Variability in rainfall threshold for debris flow after the Chi-Chi earthquake in central Taiwan, China, Int. J. Sediment Res., 24(2), 177–188, 2009. Sillmann, J. and Roeckner, E.: Indices for extreme events in projections of anthropogenic climate change, Climatic Change, 86, 83–104, 2008. Suwa, H. and Okuda, S.: Measurement of debris flows in Japan, in: Proc. IV Int. Conf and Field Workshop on Landslides, 391–400, 1985. Takahashi, T.: Mechanical characteristics of debris flow, J. Hydr. Eng. Div.-ASCE, 104, 1153–69, 1978. Takahashi, T.: Debris Flow, Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan, 1981a. Takahashi, T.: Estimation of potential debris flows and their hazardous zones, Natural Disaster Science, 3(1), 57–89, 1981b. Takahashi, T.: Debris Flow, IAHR Monograph Series, Balkema, 1991. Takahashi, T.: Initiation of flow of various types of debris flow, in: Proc. 2nd Int. Conf. on Debris flow hazards mitigation, edited by: Wieczorek, G. F. and Naeser, N. D., Balkema, Rotterdam, 15–25, 2000. Tecca, P. R., Galgaro, A., Genevois, R., and Deganutti, A. M.: Development of a remotely controlled debris flow monitoring system in the Dolomites (Acquabona, Italy), Hydrol. Process., 17, 1771–1784, 2003. Tecca, P. R and Genevois, R.: Field observations of the June 30, 2001 debris flow at Acquabona (Dolomites, Italy), Landslides, 6(1), 39–45, https://doi.org/10.1007/s10346-009-0145-8, 2009. Terlien, M. T. J.: The determination of statistical and deterministic hydrological landslide-triggering thresholds, Environ. Geol., 35(2–3), 124–130, 1998. Tognacca, C. and Bezzola, G. R.: Debris flow initiation by channel bed failure, in: Debris flow hazard mitigation: mechanics, prediction and assessment, edited by: Chen, C.-I., ASCE, 45–53, 1997. Tognacca, C., Bezzola, G. R., and Minor, H. E.: Threshold criterion for debris-flow initiation due to channel-bed failure. In: Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment, edited by: Wieczorek, G. F. and Naeser, N. D., Balkema, 89–97, 2000. Van Steijn, H.: Debris flow magnitude-frequency relationships for mountainous regions of central and Northwest Europe, Geomorphology, 15, 259–273, 1996. Van Steijn, H.: Frequency of hillslope debris flows in the Bachelard valley (French Alps), in: Programme in Geomorphology, edited by: Panizza, M., Soldati, M., Bertacchini, M., Van Asch, W., and Malmusi, S., ICP-91/ 97-I-1226/07, 11, 15–24, 1999. Wieczorek, G. F.: Effect of rainfall intensity and during on debris flows in central Santa Cruz Mountains, California, Flows/Avalanches: Process, Recognition and Mitigation, Geological Society of America, Reviews in Engineering Geology, 7, 93–104, 1987. Wilcoxon, F.: Individual comparisons by ranking methods, Biometrics Bull., 1, 80–83, 1945. Wilson, R. C. and Wieczorek, G. F.: Rainfall thresholds for the initiation of debris flows at La Honda, California, Environ. Eng. Geosci., 1(1), 11–27, 1995.