International audienceDue to its mountainous topography and its Mediterranean climate, the Provence-Alpes-Côte d'Azur (PACA) region in Southeastern France is particularly prone to flash floods, debris flows and mass movements (landslides and rockfall). A mapping system for these rainfall induced hazards has been tested by local and regional authorities and Government agencies since 2011 as part of the RHYTMME  project. This system allows, thank to radar rainfall estimation and rainfall-runoff modelling, the real-time warning and monitoring of flash floods wherever they may occur in the PACA territory. It is also intended to enable, during intense rainfall events, the localisation of the streams susceptible to generate debris flows and of the slopes the more likely to trigger landslides and/or rockfalls

Atger, F.

Azemard, P.

Batista, D.

Bel, C.

Bertrand, M.

Ecrepont, S.

Fouchier, C.

Javelle, P.

Liébault, F.

Mériaux, P.

Saint-Martin, C.

English

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Implementation of a real-time warning and mapping
system for natural hazards triggered by rainfall in
mountainous and Mediterranean areas of Southeastern
France
C. Fouchier, P. Mériaux, F. Atger, S. Ecrepont, F. Liébault, M. Bertrand, C.
Bel, D. Batista, P. Azemard, C. Saint-Martin, et al.
To cite this version:
C. Fouchier, P. Mériaux, F. Atger, S. Ecrepont, F. Liébault, et al.. Implementation of a real-time
warning and mapping system for natural hazards triggered by rainfall in mountainous and Mediter-
ranean areas of Southeastern France. 10th International Workshop on Precipitation in Urban Areas
(UrbanRain15), Dec 2015, Pontresina, Switzerland. pp.UR15-22. ￿hal-01548431￿
Rainfall in Urban and Natural Systems
10th International Workshop on Precipitation in Urban Areas
UR15-22
Implementation of a real-time warning and mapping system for natural hazards triggered by 
rainfall in mountainous and Mediterranean areas of Southeastern France
C. Fouchier*1, P. Mériaux1, F. Atger2, S. Ecrepont3, F. Liébault1, M. Bertrand1, C. Bel1, D. Batista4,
P. Azemard4, C. Saint-Martin1, P. Javelle1
1 Irstea, Aix-en-Provence and Grenoble, France
2 Météo-France, Aix-en-Provence, France
3 UMR SAS Agrocampus Ouest, Rennes, France
4 Cerema, Aix-en-Provence, France
*Corresponding author: catherine.fouchier@irstea.fr
Abstract
Due to its mountainous topography and its Mediterranean climate, the Provence-Alpes-Côte d’Azur 
(PACA) region in Southeastern France is particularly prone to flash floods, debris flows and mass 
movements (landslides and rockfalls). A mapping system for these rainfalls induced hazards has 
been tested by local and regional authorities and Government agencies since 2011 as part of the 
RHYTMME1 project. This system allows, thanks to radar rainfall estimation and rainfall-runoff 
modelling, the real-time warning and monitoring of flash floods wherever they may occur in the 
PACA territory. It is also intended to enable, during intense rainfall events, the localisation of the 
streams susceptible to generate debris flows and of the slopes the more likely to trigger landslides 
and/or rockfalls.
1. Introduction
Natural hazards occurring in mountainous areas (flash floods, debris flows, landslides, rockfalls)
are largely dependent on rainfall. A good knowledge of these hazards and the ability to forecast 
them, therefore largely depend upon an accurate estimation of precipitations. In order to improve 
the risk management in the mountainous area of Southeastern France, Irstea and Météo-France 
have led the RHYTMME project with the support of the European Union, the Provence-Alpes-Côte 
d’Azur region and the French Ministry for ecology, sustainable development and energy (Westrelin 
et al., 2013). The goal of the project is to improve the ability to forecast and localize high-risk 
rainfall-induced hazards in the Provence-Alpes-Côte d’Azur administrative area. This goal is 
currently under achievement thanks to:
the deployment of 3 X-band, dual-polarization radars in the Alpine region of southeast France, 
that allows to i) mitigate the coverage gaps of the French national radar network, mainly due to 
ground echoes and radar beam shielding by mountains, and ii) provide more accurate real-time 
quantitative precipitation estimates in this mountainous region;
the implementation of a real-time warning and mapping system for rainfall induced natural 
hazards, fed by rainfall radar data and whose outputs are made available via the Internet to 
operators in charge of risk management (local and regional authorities, emergency and rescue 
services, road and rail networks managers, ...).
We describe here the achievements of the RHYTMME project regarding rainfall and related natural 
hazards warnings. The hazards warning system informs end-users on the imminence and the
severity of hydro-meteorological events. The rainfall and flash flood hazards are real-time 
monitored while static information is currently given for debris flows, landslides and rockfall.
                                                          
1
acronym for Hydrometeorological Risks in Mediterranean and Mountainous Areas, in French: Risques 
Hydrométéorologiques en Territoires Montagnards et Méditerranéens.
Rainfall in Urban and Natural Systems
10th International Workshop on Precipitation in Urban Areas
UR15-22
2. Flash flood warnings
To address the issue of rainfall and flash-flood warning, Météo-France and Irstea have developed 
the AIGA threshold warning system which compares real-time rainfall and runoff data with 
frequency estimates of rainfall and runoff (Lavabre and Gregoris 2006, Javelle et al. 2014). The 
real-time rainfall data are the radar rainfall accumulation information for different durations (1 hour, 
2 hours, … 72 hours) provided every 15 minutes by the radar network at the spatial resolution of 1 
km2. These data are compared to regionalized rainfall frequency estimates computed, in a previous 
research work, for the same durations and at the same 1 km² spatial resolution and for different 
return periods on the whole French territory (Neppel et al. 2014). Rainfall warnings are then 
provided on maps displaying the estimated return periods of the different radar rainfall 
accumulations for the ongoing event. The real-time runoff data are provided by a distributed 
conceptual hydrological model fed by the 1-hour radar rainfall grids and run every 15 min at a 1-
km2 resolution. It produces real-time peak discharge estimates along the river network which are 
compared to regionalized flood frequency estimates previously computed (Aubert et al. 2014). 
Runoff warnings are then provided on a river network map according to the estimated return period 
of the computed peak discharge. Figure 1 shows an example of the rainfall and runoff warnings 
emitted by the RHYTMME warning system, thanks to the AIGA method, for the 26/10/2012 storm 
event which occurred in the neighborhood of the city of Toulon. The main interest of the AIGA 
method, implemented in the RHYTMME warning system, is to be able to deliver to operational 
services rainfall warnings in any 1 km2 of their area of interest and runoff warnings anywhere on 
the river network they monitor, even at ungauged locations. 
  
Fig 1: AIGA warnings emitted at 16:00 the 26/10/2012 during a storm event in the neighborhood of 
Toulon city, southern France. (a) : Estimated return periods for the 1-hour radar rainfall. (b) 
Estimated return periods for the peak flow discharge computed by the hydrological model. The 
pixel size is 1 km2.
3. Debris flow mapping
The RHYTMME warning and mapping system also provides a regional debris flow susceptibility 
map (Figure 2). This map has been produced thanks to geomatic and statistical methods 
integrating the two main predisposing factors to debris flow activity, which are the stream and 
catchment morphometry, and the sediment availability within the catchment. Within the triggering 
areas, a map of active erosion patches has been automatically produced based on the analysis of 
infrared orthophotos (IGN©) with remote sensing methods. A robust statistical model was also 
developed to predict the debris flow activity based on morphometric indicators to discriminate the 
bedload transport from the debris flow processes (Bertrand et al. 2013). The integration of these 
two factors (sediment availability and morphometric conditions) within source areas, allowed 
predicting the susceptibility to debris flow triggering. More downstream along the stream network, 
the susceptibility to debris flow propagation was computed for a given reach according to its own 
2 years < T < 10 years
10 years < T < 50 years
T > 50 years
a) AIGA rainfall warning for the 1-hour radar rainfall.
Estimated return period of rainfall:
b) AIGA runoff warning for calculated peak discharge.
Estimated return period of runoff:
2 years < T < 10 years
10 years < T < 50 years
T > 50 years
a) b)
Rainfall in Urban and Natural Systems
10th International Workshop on Precipitation in Urban Areas
UR15-22
probability of debris flow activity (its morphometric characteristics) and the susceptibility to debris 
flow activity of the reaches located upstream (recursive process). More details can be found in 
Bertrand (2014). This approach, developed by Irstea and applied in Southern Alps on each 
catchment smaller than 40 km2, has been validated with field observations.
Fig 2: Map of susceptibility to debris-flow activity within the triggering areas.
The debris flow maps – susceptibility to debris flow activity within the triggering areas (figure 2) and 
susceptibility to debris flow propagation along the stream network – can be displayed in the 
RHYTMME warning system along with the real time maps of rainfall hazard in order to identify, 
during intense events, the areas the more likely to generate debris flows.
4. Landslides and rockfall mapping
Static landslides and rockfall hazards maps, produced by Cerema, are also available in the 
RHYTMME warning and mapping system. Cerema has developed a theoretical approach based on 
a geostatistical analysis of 1712 landslides events and 1567 rockfall events, and their related
antecedent rainfall conditions, that have occurred in Southeastern France since 1900 (Batista et al. 
2013). This approach is based on the subdivision of the Provence-Alpes-Côte d'Azur region into 13 
areas showing a geotechnical homogeneity. In each of these areas, a statistical law calibrated on 
the observed data was established to assess the average number of hazards, and a simple law 
was established, relating this average number of hazards to different landslides and rockfall 
susceptibility factors, such as the slope, the exposure, the distance to the river network and the 
distance to geological faults. This regional approach enabled to assess the density of landslides 
and rockfall events in any point of the PACA area knowing the geotechnical area it belongs to and 
the values of the susceptibility factors in this point. It was then possible to draw maps displaying 
the susceptibility to landslides and rockfall based upon these densities of landslides and rockfall 
events (Figure 3).
Rainfall in Urban and Natural Systems
10th International Workshop on Precipitation in Urban Areas
UR15-22
Fig 3: Map of the susceptibility to landslides triggering, taking into account the number of observed 
events since 1900 in each homogeneous geotechnical area and susceptibility factors.
The landslides and rockfall maps can be displayed in the RHYTMME warning system along with 
the real time maps of rainfall hazard in order to identify, during intense events, the areas the more 
likely to generate landslides and/or rockfall.
5. Conclusions
The RHYTMME flood warning and mapping system has been successfully tested since 2011 by
more than 80 local and regional authorities as well as Government agencies in charge of risk 
management. On the basis of this experiment, it will be fully implemented and made available to all 
local authorities of the PACA region by the end of 2016 (approximately 1000 user authorities). 
Current research work in the field of flood warning focus now on enhancing the current hazard 
warnings by producing flood risk warnings that will take into account the vulnerability of the 
exposed territories. Current work in the fields of debris flow, landslides and rockfall now focus on 
the determination of rainfall thresholds associated with debris flow, landslides and rockfalls 
triggering. For debris flow, this work is based on the compilation of data from several debris flow 
monitoring stations recently deployed in active torrents of the French Alps (Bel et al. 2014). The 
aim is to enable to deliver debris flow, landslides and rockfall warning based on the real time radar 
rainfall estimation. 
References
Aubert Y., Arnaud P., Ribstein P. and Fine J. A. (2014). The SHYREG flow method-application to 
1605 basins in metropolitan France. Hydrological Sciences Journal 59 (5): 993-1005.
Batista D., Azemard P., Rougé A.-C., Rault C. and Giroux H. (2013). Projet RHYTMME, bilan des 
travaux réalisés sur le thème aléa mouvement de terrain, adaptation de la méthodologie à l'aléa 
chute de blocs. Technical report, 76 p.
Bel C., Liébault F., Navratil O., Bellot H., Fontaine F., Laigle D. and Navratil O. (2014). Debris-flow 
monitoring in the French Alps, Proceedings of the International Conference on Fluvial 
Hydraulics, RIVER FLOW 2014, pp. 1589-1595.
Bertrand M., Liébault F. and Piégay H. (2013). Debris-flow susceptibility of upland catchments. 
Natural Hazards 67 (2): 497-511.
Bertrand, M. (2014). Approches régionales de la susceptibilité torrentielle dans les Alpes du Sud. 
Thèse de Doctorat, Ecole Normale Supérieure de Lyon, 162 p.
Rainfall in Urban and Natural Systems
10th International Workshop on Precipitation in Urban Areas
UR15-22
Javelle P., Demargne J., Defrance D., Pansu J.  and Arnaud P. (2014). Evaluating flash-flood 
warnings at ungauged locations using post-event surveys: A case study with the AIGA warning 
system. Hydrological Sciences Journal 59 (7): 1390-1402.
Lavabre, J. and Gregoris Y. (2006). AIGA: A flood forecasting tool. Application to the French 
Mediterranean region. IAHS-AISH Publication 308: 214-219.
Neppel L., Arnaud P., Borchi F., Carreau J., Garavaglia F., Lang M., Paquet E., Renard B., 
Soubeyroux J. M. and Veysseire J. M. (2014). Comparison of extreme rainfall frequency 
analysis methods in France. La Houille Blanche (2): 14-19.
Westrelin S., Mériaux P., Dalle S., Fradon B., Jamet G. (2013). Déploiement d'un réseau de radars 
pour anticiper les risques hydro-météorologiques, La Météorologie 8 (83): 69-79.


Mise en oeuvre d'un outil d'alerte et de cartographie temps réel des aléas naturels liés aux précipitations dans les régions montagneuses et méditerranéennes du Sud-Est de la France

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Mise en oeuvre d'un outil d'alerte et de cartographie temps réel des aléas naturels liés aux précipitations dans les régions montagneuses et méditerranéennes du Sud-Est de la France

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