Variabilidade da ocorrência de deslizamentos de terra e sua relação com a precipitação na cidade de Manaus

Abstract

Since the creation of the Manaus Free Trade Zone, the Amazonian capital experienced a strong population growth due to the exodus caused by the generation of commercial and agrarian activities, having in the urban territory taken account of outlying areas, without basic infrastructure. The city is characterized as a flat region sectioned by watercourses (igarapés) with the topographical level increasing according to the distance of the Negro River in the same manner as the slope. In this way, the association of the physical characteristics of the land with the social ones formed zones of risk with 23 thousand residences (Civil Defense of Amazonas, 2013) subject to phenomena such as landslides, a problem aggravated by the marked local precipitation regime. To explore the occurrence of these natural disasters and its relationship with rains, were used records of landslides of Manaus Civil Defense, between 2010 and 2015, along with precipitation records from a network of automatic weather stations and Weather Radar precipitation estimates, in addition to satellite imagery, radio sounding data, NCEP Reanalysis and synoptic analysis. The analysis indicated a strong relation between the variables, with the seasonality of occurrences following the precipitation – greater (smaller) number of landslides occurring predominantly in the wettest months (dry). Were found in the north and east zones suffering the hardest hit, and the south central and midwest were the ones which presented less records of landslides. Considering accumulated precipitation between 24 and 96 h preceding the records made by the Civil Defense, smaller values of precipitation were observed related to landslides in the northern and eastern areas, and the other areas had highest precipitation values for triggering these disasters. The case studies revealed the landslides occurring due to cumulative precipitation on consecutive days (gradual saturation of the soil) and to more intense precipitation events in a single day. In front of the results, it is observed that the landslides are not spatially distributed in the city being the northern and eastern areas most affected due to geographical characteristics associated with precipitation. Still, it is necessary to use a longer period and different data sources to elucidate specific amounts of precipitation capable of generating natural phenomena in question.