Reconstructing extreme Late Pleistocene floods in Morocco's Inaouène Valley reveals larger discharges during terrace aggradation than both incision and modern floods

Understanding how Quaternary climate shifts shaped fluvial systems through cycles of aggradation and incision is a central theme in fluvial geomorphology. A widely observed pattern is that wetter climatic phases enhance flood discharge and transport capacity, driving valley incision. Whether this relationship is reversed in sediment-rich, semi-arid environments, however, has remained poorly constrained by direct quantitative evidence. Here we present the first quantitative reconstructions of peak flood paleodischarges from the Late Pleistocene Inaouène valley, northern Morocco. Our results show that minimum peak flood discharges during Last Glacial Maximum aggradation were at least 8487 ± 1128 m 3 /s, exceeding those of the subsequent incisional phase (≥1950 ± 181 m 3 /s) by more than four times and the maximum modern recorded flood by over 6.5 times. These findings demonstrate a sediment-supply-dominated regime, where abundant clast production from hillslopes overwhelmed even extreme floods and drove valley-wide aggradation. Incision, in turn, occurred under conditions of much lower discharge and reduced sediment input. This study provides direct, quantitative evidence linking abrupt Lateglacial climate transitions to flood-driven landscape evolution in a semi-arid Mediterranean environment. • First quantitative paleodischarge for Late Pleistocene Morocco presented. • Peak flood discharge was highest during the LGM aggradational phase. • Lateglacial incisional phase was marked by a four-fold decrease in flood magnitude. • Climate-driven sediment supply and runoff controlled aggradation and incision cycles. • Paleofloods were ~6.5× (aggradation) and ~1.5× (incision) modern maximum.