Humans, water, and the colonization of Australia

Abstract

The Pleistocene global dispersal of modern humans required the transit of arid and semiarid regions where the distribution of potable water provided a primary constraint on dispersal pathways. Here, we provide a spatially explicit continental-scale assessment of the opportunities for Pleistocene human occupation of Australia, the driest inhabited continent on Earth. We establish the location and connectedness of persistent water in the landscape using the Australian Water Observations from Space dataset combined with the distribution of small permanent water bodies (springs, gnammas, native wells, waterholes, and rockholes). Results demonstrate a high degree of directed landscape connectivity during wet periods and a high density of permanent water points widely but unevenly distributed across the continental interior. A connected network representing the least-cost distance between water bodies and graded according to terrain cost shows that 84% of archaeological sites >30,000 y old are within 20 km of modern permanent water. We further show that multiple, well-watered routes into the semiarid and arid continental interior were available throughout the period of early human occupation. Depletion of high-ranked resources over time in these paleohydrological corridors potentially drove a wave of dispersal farther along well-watered routes to patches with higher foraging returns.Sahul | Pleistocene colonization | radiocarbon | human dispersal | paleohydrological corridor

Extinction of eastern Sahul megafauna coincides with sustained environmental deterioration

“…The occupation of Sahul most-likely occurred in northwest Sahul, at least 50 ka 58,59 or as early as 65 ka 60 , with much of mainland Australia inhabited by 45 ka [61][62][63] . People most-likely dispersed across the continent via migratory routes either reflecting connectivity to available freshwater 64 or first along coastal routes and then dispersing inland 65 . Therefore, under a human-driven extinction scenario where megafauna suffer extinction shortly after human arrival it would be expected that megafauna would suffer extinction first in the north and then along the continental periphery of Sahul before extinction occurred in southern and interior regions.…”

Palaeogeography and voyage modeling indicates early human colonization of Australia was likely from Timor-Roti

“…The genetic evidence suggests that Sahul was colonized from Wallacea in one 'event' loosely constrained by genetic clocks to a range consistent with the majority of the archaeological evidence for the timing of colonization (Hudjashov et al, 2007;Malaspinas et al, 2016;Tobler et al, 2017). Once established in Sahul, dispersing populations rapidly occupied the coasts and interior (O'Connell and Allen, 2015;Bird et al, 2016). The populations in northern Sahul (modern New Guinea) were isolated from those in southern Sahul (modern Australia) soon after arrival (by at least 35ka; Malaspinas et al, 2016;or much earlier, Tobler et al, 2017), and once colonization was complete gene flow between different settled regions across Sahul reduced rapidly and dramatically thereafter (Tobler et al, 2017).…”

GSFLOW–GRASS v1.0.0: GIS-enabled hydrologic modeling of coupled groundwater–surface-water systems

“…While not an integrated hydrologic model due to its limited subsurface modeling capabilities, the Soil & Water Assessment Tool (SWAT) (Srinivasan and Arnold, 1994) incorporated GRASS GIS version 4 with an earlier and much slower version of r.watershed. Beyond this, r.watershed is typically discussed in the drainage algorithm literature (e.g., Barnes et al, 2014;Magalhães et al, 2014;Schwanghart and Scherler, 2014;Sangireddy et al, 2016), directly applied to flow-routing and cost-path calculations (e.g., Wickert, 2016;Bird et al, 2016), or included as a component of an assessment tool (e.g., Bhowmik et al, 2015;Rossi and Reichenbach, 2016). By integrating r.watershed into GSFLOW-GRASS via the r/v.stream.…”