The A2C2 system is based on few essential elements, some of which are evidently shared with Alerta-Rio: risk zoning; rainfall model and thresholds for early-warning; local and continuous measurement of rainfall; timely rainfall prediction; apparatus for alert delivery (i.e. sirens); definition and implementation of evacuation procedures; education and training of the population. Only two alert levels are defined for the A2C2 system, respectively called attention level (Índice de Atenção) and alert level (Índice de Acionamento). When the attention level is issued, the local civil defence agents are informed, via text messages, that severe weather threats are imminent and there is a high probability of an evacuation order being issued (Fig. 38.a). The alert level threshold is currently set to 40 mm of cumulated rainfall in 1 hour or 125 mm of cumulated rainfall in 24 hours. When the recorded rainfall locally exceeds the alert level, the audible early warning for the population is not issued automatically but only after a consultation between the sub-secretary of the municipal civil defence and the coordinator of CO-Rio, who also consider the updated weather forecasts to take their decision. If the evacuation order is issued, the sirens start issuing a pre-recorded warning message which includes a characteristic sound and a vocal message informing about the strong possibility of landslide occurrences and prompting the residents to evacuate the areas at high risk and move to safer places. Within each community a number of gathering places (Pontos de Apoio) exist. They are located within the community within areas not classified as at high risk and, if possible, in communal places, such as schools, sports centres or churches. Figure 38.b shows the detailed landslide risk zoning map of one of the communities (Morro da Formiga) with the location of both sirens and gathering places.