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In this paper the drainage network is considered as a geo-indicator of the environmental changes that haven taken place over a period of 23 years in three hydrographic microbasins in the São Paulo State (Brazil). The verification of the natural conditions of the physical environment was based on terrain evaluation for homogeneity of landforms and the materials associated with them. In order to identify the alterations, a temporal analysis of the drainage network morphometric variables and land use was made. The morphometric analysis indicates a decrease in the number of first-order channels and in the total length of all channels, with a consequential modification of the drainage and hydrographic densities. The losses and gains of the first-order channels were influenced by the slope, type of bedrock and presence of unconsolidated material. The catalyst for these changes was mainly the inadequate control of urban expansion and the intensive agricultural activities. [ABSTRACT FROM AUTHOR]

There is observational evidence that hydrometeorological extremes, such as heavy rainfall events, have become more frequent and intense in the last decades around the world. In Brazil, intense rainfall events that triggered flash floods and landslides were responsible for 74% of the deaths related to natural disasters in the 1991-2010 period. To evaluate Brazil's hot spots of vulnerability to these disasters, two indices were developed using three data sets: (1) climate, with IPCC climate extreme indices; (2) environmental, including land use, drainage systems, relief, slope, road density and hydrography; and (3) socioeconomic, including the Gini coefficient, Human Development Index, housing conditions and a poverty-related index. Simulations at high resolution were carried out using the Eta 20-km regional climate model nested within two global climate models: HadGEM2 ES and MIROC 5 IPCC AR5 models. For the baseline period of 1961-1990, the vulnerability indices were adjusted by means of an iterative process and were validated by comparing them to the Brazilian National Disasters Data. The two indices were also used to estimate the vulnerability up to the end of the twenty-first century, using the representative concentration pathways (RCP) 4.5 and 8.5 from the IPCC AR5 RCP scenarios. The results indicate a large increase in Brazil's vulnerability to landslides and flash floods in the context of climate change. [ABSTRACT FROM AUTHOR]