out of africa: the importance of rivers as human migration ...€¦ · out of africa: the...

Jorge A. Ramirez a,d , Tom J. Coulthard a , Nick Barton b , Mike Rogerson a , Tim Brücher c Out of Africa: the importance of rivers as human migration corridors • The route and timing of Homo sapiens exiting Africa remains uncertain. • Corridors leading out of Africa through the Sahara, the Nile Valley, and the Red Sea coast have been proposed as migration routes for humans 80,000-130,000 years ago. • During this time climate conditions in the Sahara were wetter than present day. • We use palaeoclimate rainfall and a hydrological model (CAESAR-LISFLOOD) to quantitatively test the existence of three major rivers crossing the Sahara during the time of human migration. 1. Introduction 2. Methods 3. Results 4. Conclusions Figure 1. Rainfall from an Earth System Model simulation and time series of zonally averaged precipitation for locations south of the modelled catchment. a Department of Geography, University of Hull, Hull, UK c Max-Planck-Institut für Meteorologie, Hamburg, Germany b Institute of Archaeology, University of Oxford, Oxford, UK d Department of Geography, University of Leeds, UK Figure 3. Monthly probability of surface water across the Sahara. Irharhar Middle Stone Age (including Aterian) Sept Figure 2. Simulated probability of surface water and archaeological artefacts in the Sahara. Oct Nov Dec • Well-known Sahabi and Kufrah rivers very likely flowed across modern day Libya and reached the coast. • Unexpectedly, an additional river crossed the core of the Sahara through Algeria (Irharhar river) and flowed into the Chotts basin. • Support for the Irharar as a viable migration corridor is provided by its geographic proximity to archaeological artifacts (Fig. 2). • Sahabi and Kufrah are nearly perennial, whilst the Irharhar flows for 3 months (Fig. 3). • This study provides the first quantitative analysis of the likelihood that rivers occurred during human migration out of Africa. • The Irharhar river is unique, it links locations in central Africa experiencing monsoon climates with temperate coastal Mediterranean environments where food and resources were likely abundant. Algeria Libya Tunisia Further details about this study can be found in: Contact information email: [email protected] website: https://sites.google.com/site/jramirezresearch/ Coulthard, T. J., J. A. Ramirez, N. Barton, M. Rogerson, T. Brücher (2013), Were Rivers Flowing across the Sahara During the Last Interglacial? Implications for Human Migration through Africa, PLoS ONE, 8(9). d 1.MPI-ESM Climate simulation 12 hr rainfall at 300 km grid cell resolution from climate over North Africa 125 ka BP (Fig. 1) 2. TOPMODEL hydrological model Precipitation used to generate surface runoff Water losses through infiltration & evap. 4. Model outputs Map of surface water probability for 25 years (Fig. 2) 3. Lisflood-FP hydraulic model Routes surface runoff using a 2D hydrodynamic flow model Water routed over a 1km resolution DEM video of rivers http://bit.ly/1cN5aUt

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Jorge A. Ramirez a,d, Tom J. Coulthard a, Nick Barton b, Mike Rogerson a, Tim Brücher c

Out of Africa: the importance of rivers as human migration corridors

• The route and timing of Homo sapiens exiting Africa remains uncertain.

• Corridors leading out of Africa through the Sahara, the Nile Valley, and the Red

Sea coast have been proposed as migration routes for humans 80,000-130,000

years ago.

• During this time climate conditions in the Sahara were wetter than present day.

• We use palaeoclimate rainfall and a hydrological model (CAESAR-LISFLOOD)

to quantitatively test the existence of three major rivers crossing the Sahara

during the time of human migration.

1. Introduction

2. Methods

3. Results

4. Conclusions

Figure 1. Rainfall from an Earth System Model simulation and time series of

zonally averaged precipitation for locations south of the modelled catchment.

a Department of Geography, University of Hull, Hull, UK c Max-Planck-Institut für Meteorologie, Hamburg, Germany b Institute of Archaeology, University of Oxford, Oxford, UK d Department of Geography, University of Leeds, UK

Figure 3. Monthly probability of surface

water across the Sahara.

Irh

arh

Middle Stone Age (including Aterian)

Sept

Figure 2. Simulated probability of surface water and archaeological artefacts in the Sahara.

Oct Nov Dec

• Well-known Sahabi and

Kufrah rivers very likely

flowed across modern day

Libya and reached the