Lake Victoria to the Sudd Wetland: flood wave timing, connectivity and wetland buffering across the White Nile

Mulangwa, D., Naturinda, E., Koboji, C., Zaake, B. T., Black, E. ORCID: https://orcid.org/0000-0003-1344-6186, Cloke, H. ORCID: https://orcid.org/0000-0002-1472-868X and Stephens, E. M. ORCID: https://orcid.org/0000-0002-5439-7563 (2026) Lake Victoria to the Sudd Wetland: flood wave timing, connectivity and wetland buffering across the White Nile. Hydrology and Earth System Sciences, 30 (16). pp. 5297-5325. ISSN 1027-5606 doi: 10.5194/hess-30-5297-2026

Abstract/Summary

The White Nile from Lake Victoria through Lakes Kyoga and Albert to the Sudd wetlands forms a complex connected lake-river-wetland system where flood propagation, storage, and attenuation remain poorly quantified. Following unprecedented and persistent flooding across South Sudan in 2022, this study quantified system-scale flood-wave transit time and examined how long it takes a flood wave to travel from Lake Victoria to the Sudd and how upstream storage and connectivity shape multi-year flood behaviour. Using daily lake levels, discharge, CHIRPS rainfall, and MODIS-derived inundation for 2002–2024, we tracked sequential flood peaks through the Victoria–Kyoga–Albert–Sudd cascade and mapped monthly wetland dynamics across five South Sudan sub-catchments. Flood-wave tracking showed a mean system transit time of approximately 17 months (16.84±1.95 months; range 13.0–20.9 months), substantially longer than the commonly inferred four-to-five-month timescale based on seasonal peak alignment. Segmental analysis revealed rapid transmission from Victoria to Kyoga (mean 4.2 months) but strong attenuation through the Albert–Sudd reach (mean 9.3 months), consistent with extensive floodplain storage and backwater control. Correlations between Lake Victoria peaks and downstream wetland extents strengthened markedly after 2019, with r2 exceeding 0.8 at 9–13-month lags, confirming strong hydraulic coupling and long system memory. These statistical lags complement, but do not represent, physical flood-wave transit times. The 2019–2024 high-water regime was not a series of isolated rainfall events but a multi-year propagation of excess storage initiated by the 2019 positive Indian Ocean Dipole anomaly and consecutive rainfall seasons. Lake Victoria reached exceptional peak levels of 1136.48 m a.s.l. in 2020, 1136.50 m a.s.l. in 2021, and 1136.66 m a.s.l. in 2024, each exceeding the historical 1964 maximum (1136.42 m a.s.l.). Over the same period, the Sudd Wetland exceeded its previous MODIS-era maximum extent (81 496 km2 in 2016) in every year from 2019 to 2024, reaching annual maxima of 120 680, 111 684, 111 480, 163 475, 122 292, and 116 359 km2, respectively. Flood-persistence mapping shows a shift from rainfall-driven activation in the eastern Sudd (Baro-Akobbo-Sobat–White Nile) in 2019–2020 to sustained, inflow-driven inundation across the central and western Sudd (Bahr el Jebel–Bahr el Ghazal–Bahr el Arab) during 2020–2022, consistent with water pathway activation and backwater expansion under high antecedent storage. When compared with historical episodes in the 1870s and 1960s, the persistence and spatial reach of the 2019–2024 floods rank among the most extensive in the modern record. These results redefine the White Nile as a long-memory system in which upstream storage governs downstream flood risk over multi-season timescales and challenge interpretations of flood propagation based on seasonal timing alone, offering a new empirical basis for flood forecasting, wetland management, and anticipatory action in South Sudan and across the wider basin.

Item Type	Article
URI	https://centaur.reading.ac.uk/id/eprint/131421
Identification Number/DOI	10.5194/hess-30-5297-2026
Refereed	Yes
Divisions	Science > School of Mathematical, Physical and Computational Sciences > NCAS Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
Publisher	Copernicus
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