Abstract
The monitoring of related hourly and accumulated rainfall index requires that critical thresholds of accumulated 72 hours rainfall are updated frequently according with the factors and local conditions (natural and anthropic) of each specific risk area. The importance of empirical methods is fundamental to confirm the relationship between rainfall intensity and accumulated rainfall with the mass movement events, in order to establish the critical threshold values. The present work performs an evaluation of the record data of mass movement events occurred in Sao Paulo State North coast region for a 4-year period (2014 to 2018) considering different mass movement characteristics (slope type, magnitude and impact level). Some rainfall values were obtained to show that within these parameters an event related to natural and anthropic features was triggered. A database was created, sorting source of information and municipalities monitored, to implement the correlation between the mass movement events and the rainfall values. To elaborate the event’s map, reliable record data of localization of the mass movement events was selected, as well as the nearest possible raingauges of CEMADEN (National Center for Monitoring and Early Warning of Natural Disasters); also the exact event triggering time, selection by the slope type, the magnitude and the impact level of the mass movement event. The rainfall values of these raingauges allowed the calculation of the accumulated rainfall index for 1, 3, 6, 24, 48, 72 and 96 hours, with the adoption of the 72 hours index for this work. The correlation graphics are divided by the slope type, the magnitude and the impact level of the mass movement event. Different critical thresholds appear, classifying such event by the influence level of triggering factors, natural and/or anthropic.
Highlights
With the United Nations (1993) the mass movements are one of the natural phenomena that cause the most financial impact and deaths in the world
The monitoring of related hourly and accumulated rainfall index requires that critical thresholds of accumulated 72 hours rainfall are updated frequently according with the factors and local conditions of each specific risk area
The importance of empirical methods is fundamental to confirm the relationship between rainfall intensity and accumulated rainfall with the mass movement events, in order to establish the critical threshold values
Summary
With the United Nations (1993) the mass movements are one of the natural phenomena that cause the most financial impact and deaths in the world. The mass movements assume catastrophic proportions in urban areas causing structural damages and human losses. In Brazil rainfall is the principal natural factor that causes floods, riverside collapses, intensification of erosional processes and they decisively contribute to mass movement triggering. As a result of geological risk scenarios natural processes may occur in different scales becoming disasters and catastrophes with huge material and social impact [1]. PPDC constitutes an important technical tool for management, monitoring and control of mass movement risk areas. Evacuation of vulnerable population living insusceptible areas, before the mass movement events occur, is a main prevention al action of the PPDC
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