Fluvial connectivity in the Brazilian semi-arid, Araripe sedimentary plateau

Abstract

This article aims at identifying and describing short-term connectivity scenarios in a semi-arid watershed in northeastern Brazil. The emergence of different decadal connectivity patterns is discussed, addressing the role of recent climatic inputs in triggering cut-and-fill erosive-depositional patterns within a valley bottom. A confluence stretch between a tributary and the stem channel was selected in order to analyze changes in connectivity and dysconnectivity patterns in response to climatic inputs from 2004 to 2014. The climatic behavior was assessed using the Rainfall Anomaly Index, which established dry and wet years, hence highlighting the relationship between connected and unconnected channel phases and a decennial precipitation dynamic. The years of 2004, 2008 and 2011 stand out as the rainiest and with the highest RAI values, in contrast to 2012, with a total rainfall of less than 600 mm and a RAI value below -2. The discrepancy between the 2012 rainfall total and the 2013/2014 biennium points to the relevance of this period for the reworking of alluvial deposits and connectivity resumption in the watershed. In the ephemeral drainages, connectivity is dramatically interrupted every dry season, creating fluvial disconnection. Dysconnectivity is characteristic of tropical semi-arid fluvial environments, but at landscape scale it may attest to the longevity of dry conditions, hence shall be addressed at time intervals ranging from a few days to thousands and tens of thousands of years.