The Rio de Janeiro early warning system for rainfall-induced landslides: Analysis of performance for the years 2010-2013

The paper deals with the citywide landslide early warning system "Alerta-Rio" operated by the municipality of Rio de Janeiro (Brasil). The city is divided, for warning purposes, into four alert zones. Two different alert sets co-exist within Alerta-Rio: rainfall warnings and landslide warnings. The landslide warning levels are four and they are related to an expected spatial density of landslides. The presented study focuses on the evaluation of the efficiency of the correlation models and rainfall thresholds employed by Alerta-Rio to issue the landslide warnings. The analyses refer to the four-year time frame 2010-2013; they are conducted considering the spatial and temporal distribution of rainfall, landslides and alert phases. An alert phase is herein defined as the time when the landslide warning level is associated to the possibility of diffuse or widespread landsliding within the alert zone. The performance of the system is evaluated by looking at the errors generated by the landslide alerts, computed as a function of the temporal overlap between alert phases and landslide events. Landslides are grouped in events so as to explicitly consider the extent of the landslide disasters in relation to the alerts issued. The discussion on the results of the performed analyses mainly focuses on the following issues: false and missed alerts; duration of alerts; zoning for early-warning purposes.