Improved modeling of Congo's hydrology for floods and droughts analysis and ENSO teleconnections

Abstract

Study region: The Congo River basin (CRB), the world's second-largest river system, is subject to extreme hydrological events that strongly impact its ecosystems and population. Study focus: Here we present an improved 40-year (1981-2020) hydrological reanalysis of daily CRB discharge and analyze the spatiotemporal dynamics of recent major CRB floods and droughts, and their teleconnection with El Nin similar to o-Southern Oscillation (ENSO), the dominant driver of tropical precipitation. We employ a large-scale hydrologic-hydrodynamic model (MGB) with lake storage dynamics representation and a data assimilation (DA) technique using in-situ and remote sensing observations. New Hydrological Insights: The MGB model demonstrates satisfactory performance, with KlingGupta efficiency metric of 0.84 and 0.71 for calibration and validation, respectively. Incorporating lake representation substantially enhances simulations, increasing the Pearson correlation coefficient from 0.3 to 0.63. Additionally, DA yields a -13% reduction in discharge errors via cross-validation. We find that the 1997-1998 flood impacting the south and central CRB is statistically linked to a major El Nin similar to o event during that period. However, no such association is found for the 2019-2020 flood. Severe droughts in 1983-1984 and 2011-2012, affecting northern and southern CRB respectively, exhibit strong correlation with preceding El Nin similar to o and La Nin similar to a events, with a -10-12 months lag. This study advances understanding of the intricate interplay between spatiotemporal hydrological variability in CRB and large-scale climate phenomena like ENSO.