Abstract
Abstract. Flooding in the Amazon basin is frequently attributed to modes of large-scale climate variability, but little attention is paid to how these modes influence the timing and duration of floods despite their importance to early warning systems and the significant impacts that these flood characteristics can have on communities. In this study, river discharge data from the Global Flood Awareness System (GloFAS 2.1) and observed data at 58 gauging stations are used to examine whether positive or negative phases of several Pacific and Atlantic indices significantly alter the characteristics of river flows throughout the Amazon basin (1979–2015). Results show significant changes in both flood magnitude and duration, particularly in the north-eastern Amazon for negative El Niño–Southern Oscillation (ENSO) phases when the sea surface temperature (SST) anomaly is positioned in the central tropical Pacific. This response is not identified for the eastern Pacific index, highlighting how the response can differ between ENSO types. Although flood magnitude and duration were found to be highly correlated, the impacts of large-scale climate variability on these characteristics are non-linear; some increases in annual flood maxima coincide with decreases in flood duration. The impact of flood timing, however, does not follow any notable pattern for all indices analysed. Finally, observed and simulated changes are found to be much more highly correlated for negative ENSO phases compared to the positive phase, meaning that GloFAS struggles to accurately simulate the differences in flood characteristics between El Niño and neutral years. These results have important implications for both the social and physical sectors working towards the improvement of early warning action systems for floods.
Highlights
Annual means of peak river flows are similar between the two datasets (ρ = 0.9), with the largest flows constrained to the main Amazon River and towards the junctions of its major tributaries, such as the Madeira River stemming from the south (Fig. 1a and d)
Not all dams and reservoirs across the globe have been included within GloFAS, meaning that the flood timing may differ from the observations in the simulated dataset (Ficchí and Stephens, 2019)
This paper has investigated whether the differences between positive, negative and neutral phases of various climate indices in the tropical Pacific and Atlantic Oceans significantly impact flood characteristics in the Amazon basin for the period 1979–2015
Summary
Flooding in the Amazon basin is frequently attributed to positive and negative phases of large-scale climate variability, such as the El Niño–Southern Oscillation (ENSO), and to anomalous sea surface temperatures (SSTs) in the tropical Atlantic Ocean (Richey et al, 1989; Ronchail et al, 2005a; Marengo et al, 2012, 2013; Satyamurty et al, 2013; Espinoza et al, 2013, 2014, 2019; Marengo and Espinoza, 2016; Barichivich et al, 2018). Towner et al.: Influence of ENSO and tropical Atlantic climate variability on flood characteristics commonly attributed to El Niño events and to warm SST anomalies in the tropical North Atlantic (TNA) and associated with a sustained northward position of the inter-tropical convergence zone (ITCZ; Zeng et al, 2008; Tomasella et al, 2011)
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