Spatiotemporal Analysis of an Urban Water-Supply Watershed

Abstract

Sustainable management of water and land resources is currently a top priority on the agenda of many countries around the world, which demands information on the land cover changes in watersheds. In this study, maps of 1984, 1996, 2005 and 2016 were developed using false-color composites and the Normalized Difference Vegetation Index (NDVI) to identify the main changes occurred in the Córrego Guariroba’s stream catchment. This watershed is an Environmental Protection Area since 1995, when it became the urban water supply of the state’s capital of Mato Grosso do Sul, Brazil. In order to do that, the open source software QGIS and Landsat imagery were used to determine the land use and land cover changes. This information allowed the discussion of the possible pressures and environmental consequences of the changes in these periods. The watershed has been under intense agriculture and livestock farming activities, with most of the land surface occupied by pasturelands for cattle ranching and eucalyptus forestry. Results indicate that the direct influence of human activities drastically reduced the natural cover in the area, withimplication for the compliance of the Forest Code legislation. Anthropogenic land uses represent more than 57% of the total land cover in all years, reaching 79.70% in 2005. In 2016, there was an increase in native vegetation recovery, but despite this enhancement the human land use continues high (74.09%). Part of the small gain in native vegetation is due to reforestation plans carried out from 2010. The sedimentation of the water reservoir is visible in the 2016 image, forming sandbanks that extends for about 700 m in the distal portion of the Guariroba stream. The results of this study can be applied to a possible revision of the management plan of the watershed, considering the management of its water resources integrated to environmental planning and economic development. This type of analysis may aid in the decision-making process of governmental agencies, so that watersheds used for public water supply have restrictions of land use due to the risk of reducing the quantity and quality of water.