Science of the Total Environment 655 (2019) 1089–1103 Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv Cascading processes in a changing environment: Disturbances on fluvial ecosystems in Chile and implications for hazard and risk management B. Mazzorana a,b,h,⁎,L.Piccoc,e,h,R.Rainatoc, A. Iroumé d,h,V.Ruiz-Villanuevaf,g,C.Rojasa, G. Valdebenito e,h, P. Iribarren-Anacona a, D. Melnick a,b,i a Universidad Austral de Chile, Faculty of Science, Instituto de Ciencias de la Tierra, Valdivia, Chile b CYCLO – Millennium Nucleus the seismic cycle along subduction zones, Valdivia, Chile c University of Padova, Department of Land, Environment, Agriculture and Forestry, Padova, Italy d Universidad Austral de Chile, Faculty of Forest Sciences and Natural Resources, Valdivia, Chile e Universidad Austral de Chile, Faculty of Engineering, Valdivia, Chile f University of Geneva, Institute for Environmental Sciences, Geneva, Switzerland g University of Bern, Dendrolab.ch, Institute of Geological Sciences, Bern, Switzerland h Universidad Austral de Chile, RINA – Natural and Anthropogenic Risks Research Center, Valdivia, Chile i Universidad Austral de Chile, TAQUACh – Transdisciplinary Studies of the Quaternary Period in the South of Chile, Valdivia, Chile HIGHLIGHTSHIGHLIGHTS GRAPHICAL ABSTRACT • Several Chilean rivers are disturbed by the compound effects of multiple haz- ard processes • Processcascadesinachangingenvi- ronment may result in extreme floods and complex geomorphic adjust- ments • Chilean river basins are classified ac- cording to the number of different dis- turbances they are subjected to • Paradigmatic examples of occurred process cascades are presented, de- scribed and discussed • Adaptations of hazard and risk assessment procedures are necessary to account for such process interactions article info abstract Article history: The compound hazard effects of multiple process cascades severely affect Chilean river systems and result in a Received 12 September 2018 large variety of disturbances on their ecosystems and alterations of their hydromorphologic regimes leading to Received in revised form 14 November 2018 extreme impacts on society, environment and infrastructure. The acute, neo-tectonically pre-determined suscep- Accepted 15 November 2018 tibility to seismic hazards, the widespread volcanic activity, the increasing glacier retreat and the continuous ex- Available online 20 November 2018 posure to forest fires clearly disturb entire riverine systems and concur to trigger severe floods hazards. With the fi fl Editor: Deyi Hou objective to re ne the understanding of such cascading processes and to prospect feasible ood risk management strategies in such a rapidly changing environment we first classify the large river basins according to a set of dis- turbances (i.e. volcanic eruptions, earthquakes, glacier lake outburst floods, wild fires and mass movements). ⁎ Corresponding author at: Edificio Pugín, Faculty of Science, Campus Isla Teja, Universidad Austral de Chile, Valdivia, Chile. E-mail address: [email protected] (B. Mazzorana). https://doi.org/10.1016/j.scitotenv.2018.11.217 0048-9697/© 2018 Elsevier B.V. All rights reserved. 1090 B. Mazzorana et al. / Science of the Total Environment 655 (2019) 1089–1103 Keywords: Then, we describe emblematic cases of process cascades which affected specific Chilean drainage basins and re- Process cascades sulted in high losses as tangible examples of how the cascading processes may unfold in other river basins with Compound events similar characteristics. As an attempt to enrich the debate among management authorities and academia in Chile, Natural hazards and elsewhere, on how to sustainably manage river systems, we: a) highlight the pivotal need to determine the Process connectivity possible process cascades that may profoundly alter the system and b) we suggest to refine hazard and risk as- Chile sessments accordingly, accounting for the current and future exposure. We advocate, finally, for the adoption of holistic approaches promoting anticipatory adaptation which may result in resilient system responses. © 2018 Elsevier B.V. All rights reserved. 1. Introduction particularly challenging. For this reason, in Section 4 we discuss a clear set of priorities for natural hazard and risk assessment as basic require- Aiming at promoting a sustainable development, the Chilean Minis- ments for an enhanced preparedness throughout the different manage- try of Public Works has recently launched a comprehensive and partic- ment phases of the “risk cycle” (compare www.nahris.ch; Carter, 1991; ipatory planning process, called “Plan Chile 30/30”, which explicitly Alexander, 2000; Kienholz et al., 2004; Fuchs, 2009b). Acknowledging considers the paramount importance of water in the context of urban that still considerable knowledge gaps need to be filled to comprehen- and rural planning and establishes the assessment of the associated nat- sively understand from a holistic perspective the multiple impacts gen- ural and anthropogenic risks as an essential requirement. This plan con- erated by such process cascades we also outline specificrequirements stitutes a long-term vision for the definition of the requirements in that should be contained in future research agendas. terms of public infrastructure and water to be fulfilled until the year 2030. This public-private participative plan was conceived as an at- 2. Processes and associated disturbances in Chilean drainage basins tempt for decentralization, considering the local needs, as an integral part of a strategic plan (Ministerio de Obras Públicas, 2014). The assess- 2.1. Processes ment of compound hazard effects of multiple process cascades that se- verely affect Chilean river systems is a prerequisite to achieve the 2.1.1. Earthquakes above mentioned, ambitious, developmental goals. Hazard assessment The Chilean territory has been regularly affected by earthquakes is, however, particularly challenging when different processes interact, (Barrientos, 2007), which are associated with the subduction zone and their coupled effects not simply superpose in space and time but where the Nazca Plate converges below the South American Continental rather compound in complex and not yet understood ways Plate at a rate of about 70 mm/year (Angermann et al., 1999). This (Zscheischler et al., 2018). boundary condition extends from northern Chile to Taitao (19-47S). In Despite a relatively long tradition in applying the risk concept in dif- addition to the subduction zone megathrust fault, which constitutes ferent mountain and lowland regions of the world (Kienholz et al., the primary source of great (Moment Magnitude - Mw N 8) and giant 2004; de Vries, 2007; Fuchs, 2009a, 2009b, de Vries, 2011; Fuchs et al., (Mw N 9) earthquakes in Chile, a few secondary seismic sources may 2015, Mazzorana et al., 2014), losses due to flood hazard processes are pose a high but local hazard to drainage systems (e.g., crustal and intra- growing (Barredo, 2009) even if there is uncertainty regarding the over- plate activity). Megathrust earthquakes commonly affect large areas all increasing or decreasing trends in their frequency or magnitude (N104 km2). Such giant events reoccur more periodically than expected (Fuchs, 2009a; Gall et al., 2009; Hirsch and Archfield, 2015; Berghuijs according to recent paleoseismic studies in southern Chile (Moernaut et al., 2017). Recently, Chile has experienced large and extreme events et al., 2018). In relation to their potential to trigger complex process cas- resulting in important hazards and causing significant environmental cades their spatial distribution becomes, in addition to their magnitude, disturbances, damages and economical losses. More than 70 earth- a key issue to be considered. With respect to the generated distur- quakes with magnitude larger than 7 have been reported, including bances, the impact of such giant seismic events remains clearly detect- the strongest recorded by modern seismology, the Valdivia 1960 earth- able in the geomorphology of river systems (Yanites et al., 2010). quake (Mw 9.5), and recently the 2010 Maule (Mw 8.8) event. At least Changes range from abrupt alterations of the drainage system through 15 ice-dammed lakes have failed since the eighteenth century trigger- an intensified landslide activity, vertical shifts macroscopically changing ing extraordinary outburst floods (Iribarren Anacona et al., 2015). the rivers long profile (i.e. knickform initiation and distribution) and Some of the N90 active volcanos located in the country erupted in the planform, stream offsets (i.e. displacements of the river basin outlets last years, such as the Villarica and Calbuco volcanos with major erup- form the previously connected fan apexes) (Bierman and tions in 2015. Wildfires have extensively affected forested areas. More Montgomery, 2014). These alterations have to potential to dramatically than 8000 fires were responsible for burning approximately and long lastingly change the structural and functional connectivity of 130,000 ha in 2014 (Úbeda and Sarricolea, 2016) and 587,000 ha during entire river basins (Cavalli et al., 2013). Further, great and giant the summer season 2016–2017 (Conaf, 2017; Onemi, 2017). Cata- megathrust earthquakes are commonly associated with tsunamis that strophic flooding and mass movements were triggered by heavy precip- pose an additional hazard to coastal areas with the potential to disrupt itation, such as the 2015