Extreme precipitation events and geomorphic adjustments in the riverscape: A case study in Southern Brazil

Abstract

Extreme precipitation events can cause geomorphic adjustments in the riverscapes. As a result of the increase in severity and frequency of these events in climate change scenarios, riverscapes may become more sensitive to the geoforms sculpting processes. Consequently, communities in the river valleys may be adversely affected, worsening socio-environmental problems arising from these places’ occupation. This work investigates the relationship between events classified as heavy rainfall and persistent rainfall and geomorphic adjustments in the riverscape. A section of the Itapocu River in southern Brazil between latitudes 26°25’S and 26°32’S was used as a case study. Extreme events recorded in pluviometers’ historical series located around the study area were selected and characterized. These events occurred between 01/30/2019 and 04/15/2019; 11/15/2020 and 12/30/2020; 02/23/2021 and 03/10/2021. The geomorphic adjustments were identified by selecting Sentinel-2 orbital imagery. The satellite images were applied in the river valley geoforms vectorization and correlation among transverse and longitudinal sections to the river valley. The analysis of fluvial sensitivity went through the adjustments’ significance evaluation by the Wilcoxon Signed Rank Test. The results indicated that the river presented adjustments related to extreme precipitation events. These adjustments were identified as channel migration, channel expansion, channel narrowing, river bar expansion, and river bar narrowing. However, only channel migration, channel expansion, and channel narrowing were significant. In 2019, 82.03% of the river was significantly affected by the events, while in 2020 and 2021, events impacted 57.67% and 64.72% of the river, respectively.