Exploring the roles of recorded unprecedented rainfall-runoff characteristics and uplifted riverbeds in the catastrophic 2022 Pakistan megaflood

Abstract

Catastrophic floods triggered by extreme monsoonal rainfall have increasingly posed challenges in flood management, particularly in low-income nations like Pakistan. The 2022 megaflood exposed substantial gaps in understanding the interplay between rainfall, sediment dynamics, and flood amplification processes. This study investigates the causes and impacts of the event, focusing on floodwater sources, geomorphological changes, and future risks and mitigation strategies. A multifaceted approach combined with remote sensing, field observations, hydro-meteorological data, and climate models was employed. In July–August 2022, the lower Hindukush, Koh-e-Suleman, and Kirther ranges experienced rainfall of 200–300 mm, up to 726% above historical averages (1991–2021). This high-intensity rainfall triggered high-magnitude discharges from approximately 1250 streams, 58 % of which were primary contributors with discharge at 4000–5000 m³/s for nearly a month, causing 80%–85% of downstream damage and expanding the flooded area to 49,711 km². Some streams recorded 5–6 m flood levels, resulting in sedimentation deposition of 0.8–1 m in residential areas and about 2 m in the streambeds. Deposition downstream and along the Indus River reached 1.5–2 m, intensifying flood risks by reducing channel capacity and increasing water levels during flood events. Streambed uplift and sediment deposition emerged as critical factors amplifying flood magnitude, severity, and inundation, with floodwater levels rising by up to 2.4–3 m in some areas, posing severe risks for future events. These findings highlight the need to revise traditional flood risk models, which often overlook sediment dynamics and underscore the future challenges posed by ongoing sediment deposition and climate change, which are expected to exacerbate flood risks in the coming decades. The study emphasizes the importance of sediment management, river erosion control, and post-event interventions. Prioritizing flood management, enhancing early warning systems, and investing in resilient infrastructure are essential strategies to protect communities and ensure long-term safety.