SA1-Rio de Janeiro, Brazil

HOME

Two different early warning systems are currently adopted in Rio de Janeiro: Alerta-Rio, covering the whole territory of the municipality divided, for warning purposes, in four zones; A2C2 (Sistema de Alerta e Alarme Comunitário para Chuvas Fortes), which is currently employed in 103 informal communities—i.e. favelas—of the city. Alerta-Rio is an alert system aiming at warning the population for severe weather conditions which may induce flash floods or landslides. The A2C2 system is an alert and alarm system having the objective to temporary evacuate the population from areas mapped at high risk whenever the probability of rainfall-induced landslides in those areas, and thus the related risk for the human life, increases to intolerable levels.

1 The setting

The rainfall monitoring system of Alerta-Rio currently comprises a telemetric network of 33 meteorological monitoring stations, installed in various areas of the city, and two meteorological radars. The monitoring stations measure rainfall and other meteorological variables (wind, humidity, temperature and air pressure) at 15 minute intervals. Concerning the radars, the oldest one is owned by the Brazilian Air Force, it is located at an altitude of approximately 1800 m above sea level within the municipality of Petropolis—about 60 km from Rio de Janeiro—and it has been operational since 1998; the most recent one is owned by the municipality of Rio de Janeiro, it became operational in 2010 and it is located at an altitude of approximately 600 m a.s.l. within the city boundaries. The latest acquisition substantially upgraded the accuracy of the rainfall forecasts issued by Alerta-Rio for a number of reasons, among which: the newest radar can detect rainfall nuclei occurring at much lower elevations (600 vs. 1800 m a.s.l.); images from the Air Force radar are available to the Alerta-Rio meteorologists only at 15 to 20 minutes intervals, while the new radar images are generated every two minutes and are, therefore, much more useful for reliable short term rainfall forecasts. More recently, two new tools were acquired, and are currently being tested, to help with short-term weather forecasts: a high-resolution weather forecasting software developed by IBM, called PMAR; a lightning detection system, known as StreamerRT, developed by Earth Networks.

The territory of the municipality of Rio de Janeiro, about 1.200 km2, is divided, for warning purposes, in four zones: Baia de Guanabara, Zona Sul, Baia de Sepetiba and Jacarepaguà (Fig. 36).

Figure 36: Subdivision of the municipal territory for early warning purposes.

2 The modelling

The oldest published studies dealing with rainfall thresholds for defining the landslide probability of occurrence in Rio de Janeiro date back to 1997, when a relationship between rainfall and landslides was established based on 65 past events and rainfall data from a set of five rain gauges (d’Orsi et al., 1997). This preliminary study led to the first criteria for landslide warning adopted by GEO-RIO which considered the following two rainfall variables: 24-hour and 96-hour antecedent cumulated rainfall (Ortigao et al., 2001). The criteria assumed a 24-hour antecedent cumulated rainfall threshold dependent on the 96-hour antecedent cumulated rainfall by means of a function linearly increasing up to a maximum value and then asymptotically decreasing to zero. The next development occurred in 2004, when a third rainfall variable, i.e. the monitored hourly cumulated rainfall, was added to the previous two, following a detailed analysis of data from about 800 landslides of different typologies (d’Orsi et al., 2004). The rainfall variables were, since then, treated independently and different thresholds and a series of either/or rules were established to define warning levels associated to landslide probability of occurrence. These thresholds have been recently refined following new correlation analyses between monitored rainfall and landslide events. Table 3 show the current rainfall thresholds and the associated landslide probability warning levels adopted by GEO-RIO.

Table 3: Rainfall thresholds currently adopted by GEO-RIO to define landslide warning levels during heavy rainstorms.

3 The warning strategy

Two different alert sets co-exist with the Alerta-Rio early warning system: rainfall alerts (Alerta Para Chuva) and landslide occurrence alerts (Alerta Para Escorregamento). Concerning the first one, the alert levels are four and the warnings are issued according to short term rainfall forecasts. The four stages of rainfall warnings are: Vigilância (no rain / light rain in the next 6 hours; code color green), Atenção (moderate, occasionally strong rainfall in the following hours; code color yellow), Alerta (strong rainfall with possible isolated landslides and floods; code color red), Alerta Máximo (very strong rainfall with possible diffuse landsliding and flooding; code color black). Concerning the probability of landslide occurrence, another set of warnings exist, which is based on the comparison between rainfall measured by the meteorological monitoring stations and defined rainfall thresholds (see Table 2.3). Also in this case, four warning levels are used to define the probability of landslide occurrence: Baixa (mass movements not directly triggered by rainfall - code color green), Média (occasional occurrences of landslides, mass movements triggered by rainfall, predominantly in artificial slopes, areal distribution not significant), Alta (diffuse occurrence of landslides, mass movements triggered by heavy rains in natural and artificial slopes, moderate to high areal distribution), Muito Alta (widespread occurrence of landslides, mass movements triggered by heavy rains in natural and artificial slopes and especially on roads cuts, very high areal distribution).

3 The response strategy

When weather forecasts indicate a high probability of significant rainfall events an alert level depending on the intensity expected is issued. Simultaneously, if the pluviometric network measures rainfall values exceeding the thresholds, the system Alerta-Rio emits warnings concerning the probability of landslide. These types of advertisements can be broadcast in generalized form for the entire metropolitan area of Rio de Janeiro or with reference to an individual area of alert. To promote timely communication of alerts to the population, radio and television operators have the possibility to access the main operations room of the coordination center of Rio de Janeiro (Rio-CO) from which, during emergency situations, journalists promptly update listeners on the basis of information provided them in real-time. Additional communication channels used by the GEO-Rio for the dissemination of alerts are: e-mail, texts and twitter to registered users and update in real time of a website in which there are both alert both rainfall and meteorological data acquired. In figure 37 is shown a schematic operation of the Alerta-rio system.

Figure 37: Alerta-rio system.

References

Barros W.T., Amaral C., d’Orsi R.N. (1992). Landslides Susceptibility Map of Rio de Janeiro. Proc. Int. Symp. Landslides, Christchurch, New Zealand, 869-871.

D’Orsi R.N. (2012). Landslide risk reduction measures by the Rio de Janeiro city government. Improving the assessment of disaster risks to strengthen financial resilience, Special Joint G20 Publication, Government of Mexico and World Bank, open publication, 77-91 (https://www.gfdrr.org/G20DRM).

D’Orsi R.N., Feijó R.L., Paes N.M. (2004). 2,500 Operational days of Alerta Rio system: history and technical improvements of Rio de Janeiro warning system for severe weather. Proc. IX Int. Symp. Landslides, Rio de Janeiro, Brazil, 831-836.

Calvello M, d’Orsi RN, Piciullo L, Paes N, Magalhaes MA, Lacerda WA (2015b) The Rio de Janeiro early warning system for rainfall-induced landslides: analysis of performance for the years 2010–2013. Int J Disast Risk Reduc 12:3–15. doi:10.1016/ j.ijdrr.2014.10.005