Limiares críticos de chuvas no município de Maceió-AL: uma correlação estatística entre pluviosidade e movimentos massa

Abstract

The relationship between rainfall and landslides represents an important tool for creating warning systems and developing a mass movement mitigation plan in the city of Maceió (AL). Mass movements are those defined as being natural events of soil and/or rock movement along a slope under the direct action of gravity, which can be added by other transport agents, which reduce the resistance of slope materials and can induce a plastic and fluid behavior of the soils. Landslides result from the disruption of equilibrium conditions, defined by geological, geomechanical and climatic factors, with rainfall playing a fundamental role in triggering these processes. The construction of the proposed model started from the analysis and compilation of rainfall events that resulted in landslide processes in the municipality, based on the evaluation of historical series of rainfall data and a database formed from the occurrences of landslides attended in the County. Making an empirical correlation of the data that will be considered the accumulated rainfall prior to landslides of 24h (mm/24h), 48h (mm/48h), 72h (mm/72h), 96h (mm/96h) 120h (mm/120). Based on the municipality's rainfall data, provided by NWSA (National Water and Sanitation Agency) and the georeferenced landslide data provided by the municipality's Civil Defense, scatter plots were prepared in Excel to understand the correlation curve between the phenomena to define the correlation and critical rainfall thresholds, maximum or minimum necessary to trigger rupture processes, being of paramount importance for the monitoring of risk areas, acting directly in the preservation of human lives. The minimum amount of accumulated precipitation necessary to cause accidents in the region was estimated at 48.2mm/6 days. The value defined as the level of attention, or the value with the highest probability of occurrences of landslides was 90.3mm/5 days in Maceió. In the analysis of georeferenced landslides and the elements of the physical environment, the following stood out: urban soils, the Barreira Formation and the Erosive Edges. Finally, it was possible to establish the correlation between rainfall and landslides allowing to determine a critical rainfall threshold for the municipality, combining the daily rainfall intensity (mm/day) with the rainfall accumulated in the previous 5 days (mm/5d), with a numerical ratio PD = 353.9 PA-0.368.