Cellular automata and Agent-based models in response to different environmental problems: a review on French research over the last ten years

Cellular Automata (CA) and Agent-Based Models (ABM) are used to better assess patterns and processes result-ing from environmental interactions using simple rules. Over the last ten years, the applications have been carriedout on various complex systems: flash floods, fire propagation, river meandering, landscape evolution... The fre-quent use these applications demand are supported by an array of advances in field outside of physical geographyas physics, computer sciences and mathematics. This communication presents common, singular and innovativeapplications observed in French research. On one hand, the CA RuiCells aims at understanding the spatial hy-drological behaviours in all points of one catchment, linking impacts due to basin forms and slopes through localto global scales (Delahaye et al., 2007). The CA Soda has been developed to measure erosion at fine scale, lessthan a few meters (Vallette, 2006). Smoothed-particules can also be implemented in CA to improve dynamics orhydrological fluxes (Drogoul, 1995). On the other hand, ABM appears in geomorphology after first initiatives inecology, sociology or human geography in the 1990's. Modules of CATCHSCAPE allow to simulate the hydrolog-ical system with its distributed water balance, irrigate schemes management, crop and vegetation dynamics (Bécuet al. 2008). For alluvial plains, ABM can also be used to simulate processes between independent interacting enti-ties which behave according to the local environment (Teles et al., 1999). At the opposite, many models have beendeveloped in other countries, as for simulating erosive thresholds (Favis-Mortlock, 1998), lava dynamics (Avolioet al., 2006), fluvial meandering (Coulthard and Van de Wiel, 2006), evolution of coasts (Dearing et al., 2005) anddunes (Thomas and Nicholas, 2007). Consequently, this communication addresses the debate on two questions:why French geomorphologist researchers are late in applying CA and ABMs, and is the simplification in processeshad led to change research questions or to offer new perspectives

Risk as a process: a history informed hazard planning approach applied to the 2018 post-fire debris flows, Montecito, California

Historical information about floods is not commonly used in the US to inform land use planning decisions. Rather, the current approach to managing floods is based on static maps derived from computer simulations of the area inundated by floods of specified return intervals. These maps provide some information about flood hazard, but they do not reflect the underlying processes involved in creating a flood disaster, which typically include increased exposure due to building on flood-prone land, nor do they account for the greater hazard resulting from wildfire. We developed and applied an approach to analyze how exposure has evolved in flood hazard zones in Montecito, California, an area devastated by post-fire debris flows in January 2018. By combining historical flood records of the past 200 years, human development records of the past 100 years, and geomorphological understanding of debris flow generation processes, this approach allows us to look at risk as a dynamic process influenced by physical and human factors, instead of a static map. Results show that floods after fires, in particular debris flows and debris laden floods, are very common in Montecito (15 events in the last 200 years), and that despite policies discouraging developments in hazard areas, developments in hazard zones have increased substantially since Montecito joined the National Flood Insurance Program in 1979. We also highlight the limitation of using conventional Flood Insurance Rate Maps (FIRMs) to manage land use in alluvial fan areas such as Montecito. The knowledge produced in this project can help Montecito residents better understand how they came to be vulnerable to floods and identify action they are taking now that might increase or reduce their vulnerability to the next big flood. This science-history-centric approach to understand hazard and exposure evolution using geographic information systems (GIS) and historical records, is generalizable to other communities seeking to better understand the nature of the hazard they are exposed to and some of the root causes of their vulnerabilities, in other words, both the natural and social processes producing disasters

Social and Hydrological Responses to Extreme Precipitations: An Interdisciplinary Strategy for Postflood Investigation

International audienceThis paper describes and illustrates a methodology to conduct postflood investigations based on interdisciplinary collaboration between social and physical scientists. The method, designed to explore the link between crisis behavioral response and hydrometeorological dynamics, aims at understanding the spatial and temporal capacities and constraints on human behaviors in fast-evolving hydrometeorological conditions. It builds on methods coming from both geosciences and transportations studies to complement existing post-flood field investigation methodology used by hydrometeorologists. The authors propose an interview framework, structured around a chronological guideline to allow people who experienced the flood firsthand to tell the stories of the circumstances in which their activities were affected during the flash flood. This paper applies the data collection method to the case of the 15 June 2010 flash flood event that killed 26 people in the Draguignan area (Var, France). As a first step, based on the collected narratives, an abductive approach allowed the identification of the possible factors influencing individual responses to flash floods. As a second step, behavioral responses were classified into categories of activities based on the respondents' narratives. Then, aspatial and temporal analysis of the sequences made of the categories of action to contextualize the set of coping responses with respect to local hydrometeorological conditions is proposed. During this event, the respondents mostly follow the pace of change in their local environmental conditions as the flash flood occurs, official flood anticipation being rather limited and based on a large-scale weather watch. Therefore, contextual factors appear as strongly influencing the individual's ability to cope with the event in such a situation

Floods 2 : risk management

Crowdsourcing and crisis-mapping are concepts supported by the involvement of a large number of persons that enable, in a voluntary way, consolidation of information collected in situ during the course and progress of a phenomenon (such as a flood for example). The term 'volunteerism' is generally used to refer to activities that are non-obligatory (there is no contractual, familial or friendship obligation between the helper and the helped, nor coercion). Data collected is often of a geographical nature, and the tools used for collection (internet, mobile technologies), and publication of this data (websites, map platforms), enable it to be shared instantly and quickly. When floods occur, this input can help to assess the seriousness of a situation, and to guide disaster relief operations for victims

Introduction to the thematic issue: "Quantitative hydro-geomorphology"

Co-Guest Editors would like to thank the authors who answered this call for papers and the eighteen anonymous reviewers. We also want to deeply thank Gilles Arnaud-Fassetta, Editor in Chief of the journal Géomorphologie: relief, processus, environnement for his confidence and his availability. Since a few decades hydro-geomorphologists use quantitative tools to estimate flows, water or sediments passing across river basins. They focus on the upstream/downstream interactions and on the numerou..

Apports d'un indicateur d'exposition à une meilleure anticipation des dommages avec la méthode AIGA d'avertissements des crues : une étude de cas dans le Sud de la France

International audienceOn the 3rd October 2015, heavy localized precipitations have occurred in South Eastern France leading to major flash floods on the Mediterranean coast. The severity of those floods has caused 20 fatalities and important damage in almost 50 municipalities in the French administrative area of Alpes-Maritimes. The local recording rain gauges have shown how fast the event has happened: 156 mm of rain were recorded in Mandelieu-la-Napoule and 145 mm in Cannes within 2 hours. As the affected rivers are not monitored, no anticipation was possible from the authorities in charge of risk management. In this case, forecasting floods is indeed complex because of the small size of the watersheds which implies a reduced catchment response time. In order to cope with the need of issuing flood warnings on un-monitored small catchments, Irstea and Météo-France have developed an alternative warning system for ungauged basins called the AIGA method. AIGA is a flood warning system based on a simple distributed hydrological model run at a 1 km² resolution using real time radar rainfall information (Javelle, Demargne, Defrance, Pansu, & Arnaud, 2014). The flood warnings, produced every 15 minutes, result of the comparison of the real time runoff data produced by the model with statistical runoff values. AIGA is running in real time in the South of France, within the RHYTMME project (https://rhytmme.irstea.fr/). Work is on-going in order to offer a similar service for the whole French territory. More than 200 impacts of the 3rd October floods have been located using media, social networks and fieldwork. The first comparisons between these impacts and the AIGA warning levels computed for this event show several discrepancies. However, these latter discrepancies appear to be explained by the land-use. An indicator of the exposure of territories to flooding has thus been created to weight the levels of the AIGA hydrological warnings with the land-use of the area surrounding the streams for which the warnings are issued. This paper aims to explain how this indicator has been created and to assess its relevance with the example of the 3rd October 2015 flood. By completing this approach, the AIGA warnings may characterize not only the flood hazard but more inclusively the risk of flooding, allowing to forecast this type of event