Global warming as well as recent droughts and floods threaten large populations along the Nile Valley. Understanding how such a large river will respond to an invigorated hydrological cycle is therefore a pressing issue. Insights can be gained by studying past periods with wetter and warmer conditions. A recent study by a research team led by the German Research Centre for Geosciences GFZ, including the Alfred Wegener Institute and the University of Innsbruck participated, provides insights into this. A sediment core from the Nile Valley shows that in the past, a wetter climates led to very strong and weak floods and a highly instable river system, which may have rendered the Nile valley uninhabitable. The study has been published in the journal Nature Geoscience.
The iconic floods of the Nile River are often associated to the development of irrigation and agriculture in pharaonic Egypt. However, even today, seasonal rainfall and flooding remain crucial to sustain large populations in the Nile Valley, from the Equator to the Mediterranean coast. Climate models predict a large increase in monsoonal rainfall in this region due to global warming for all climatic scenarios. To address these threats in the future, it is important to understand how major river systems will respond to increased rainfall. Insights can be gained from studying ancient times that are known to have been wetter and warmer than the present time.
To gain access to these ancient times, Cécile Blanchet and colleagues from the GFZ German Research Centre for Geosciences, Monica Ionita (Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, AWI) and Arne Ramisch (University of Innsbruck) have analyzed a unique sediment core. It comes directly from the mouth of the Nile and records seasonal flooding from the North African wet period eleven to six thousand years ago. These brought with them varying amounts of fluvial particles, which were preserved in the form of fine layers.
The analyses reveals that wetter climates led to very strong and weak floods and a highly instable river system, which may have rendered the Nile valley uninhabitable. Although intensified, flood variability was paced by similar climatic forcing as today, operating on annual to multi-decadal timescales. Data from the past could help to make the occurrence of such extreme events more predictable, which can help to reduce the risks to local populations through reliable forecasting tools and adequate infrastructure.
Original publication:
Blanchet, C.L., Ramisch, A., Tjallingii, R. et al. Climatic pacing of extreme Nile floods during the North African Humid Period. Nat. Geosci. (2024). https://doi.org/10.1038/s41561-024-01471-9