Physical-geographical variables and the implications on environmental vulnerability in the Guamá River Sub-Basin, Pará, Brazil

Abstract

The hydrographic network of the Guamá River is a very complex hydrological system due to the interrelationship between rural and urban environments that suffer anthropic influence in different degrees, mainly due to economic activities. In this context, the objective of the present study was to diagnose the use and occupation of the soil, morphometry and rainfall in the area of the sub-basin of the Guamá River (northeastern Pará). Then, based on the information of selected physical and geographic variables, establish a diagnosis of environmental vulnerability. Remote sensing processes and secondary data were used for the morphometric study (Shuttle Radar Topography Mission - SRTM), land use and occupation (images from the Sino-Brazilian Earth Resources satellite CBERS-4 - China-Brazil Earth Resources Satellite) and precipitation for the years 2015 to 2017 (CHIRPS - Climate Hazards group Infrared Precipitations with Stations). For the study of the cartographic distribution of environmental vulnerability, the crossing of base maps of geology, type of soil, relief, type of vegetation cover, climate and land use and occupation was applied through the operation of map algebra and considering the principle ecodynamic analysis. The study area showed physical characteristics unfavorable to water supply because it is located at low altitude and is not well drained. However, the characteristics of the relief suggest the favor of low water flow and low susceptibility to erosion and flooding. Regarding the amount of rain, high precipitation values were recorded (minimum annual average of 2,295 mm and maximum of 2,729 mm), which are not distributed equally throughout the year and demonstrate agreement with the expected behavior for the region (rainy period between months December and May and the least rainy period between June and November). A higher percentage (approximately 57%) of an area classified as exposed soil and undergrowth was noted than an area classified as dense or secondary vegetation (approximately 42%). The reduction and the absence of primary vegetation cover in some sections of the study area were evidenced and the importance of monitoring this type of coverage for the region is demonstrated. In the Guamá River sub-basin, low, medium and high vulnerability areas had the highest occurrence percentages (approximately 28%, 29% and 26%, respectively); and, they represent areas with constant action of pedogenic and morphogenic processes. Thus, the importance of controlling the expansion of human activities, removing primary vegetation and respecting the legal precepts of Brazilian environmental legislation is emphasized.