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. 2012 Jun 26;109(26):E1688-94.
doi: 10.1073/pnas.1112743109. Epub 2012 May 29.

Fluvial landscapes of the Harappan civilization

Affiliations

Fluvial landscapes of the Harappan civilization

Liviu Giosan et al. Proc Natl Acad Sci U S A. .

Abstract

The collapse of the Bronze Age Harappan, one of the earliest urban civilizations, remains an enigma. Urbanism flourished in the western region of the Indo-Gangetic Plain for approximately 600 y, but since approximately 3,900 y ago, the total settled area and settlement sizes declined, many sites were abandoned, and a significant shift in site numbers and density towards the east is recorded. We report morphologic and chronologic evidence indicating that fluvial landscapes in Harappan territory became remarkably stable during the late Holocene as aridification intensified in the region after approximately 5,000 BP. Upstream on the alluvial plain, the large Himalayan rivers in Punjab stopped incising, while downstream, sedimentation slowed on the distinctive mega-fluvial ridge, which the Indus built in Sindh. This fluvial quiescence suggests a gradual decrease in flood intensity that probably stimulated intensive agriculture initially and encouraged urbanization around 4,500 BP. However, further decline in monsoon precipitation led to conditions adverse to both inundation- and rain-based farming. Contrary to earlier assumptions that a large glacier-fed Himalayan river, identified by some with the mythical Sarasvati, watered the Harappan heartland on the interfluve between the Indus and Ganges basins, we show that only monsoonal-fed rivers were active there during the Holocene. As the monsoon weakened, monsoonal rivers gradually dried or became seasonal, affecting habitability along their courses. Hydroclimatic stress increased the vulnerability of agricultural production supporting Harappan urbanism, leading to settlement downsizing, diversification of crops, and a drastic increase in settlements in the moister monsoon regions of the upper Punjab, Haryana, and Uttar Pradesh.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Large-scale morphology of the Indo-Gangetic Plain (for altitudes, pattern of colors repeats every 10 m to 300 m in height; higher landscape in gray). Convex downslope, aggradational landscapes (e.g., Tista = t; Kosi = k; Gandak = g) have a lighter mask, whereas incisional landscapes have a red mask. (B) Along-channel longitudinal profiles for the Indus and its Punjab tributaries. (C) Hydrographs for the Indus and confluent Punjab tributaries (Panjnad River). (D) Profiles across the extended Indus plain (in meters above sea level). River channel locations are identified on the profiles, as are locations and ages of studied fluvial sedimentary deposits in Sindh and Punjab (ages in thousands of years).
Fig. 2.
Fig. 2.
(A) Morphology of the western Indo-Gangetic plain with interfluves (in gray mask), incised valleys (no mask), terrace edges (as dashed black lines), and active and fossilized river channels (in blue). Legend further indicates sampling locations and types. (B) Pre-Harappan sites with modern region names, chronological information (youngest fluvial deposits at all sites), and selected town names.
Fig. 3.
Fig. 3.
Settlements on morphological units of the western Indo-Gangetic plain (see Fig. 2 for color conventions and legend). (A) Early and Mature Harappan sites, with names of some major urban centers: D = Dholavira; M = Mohenjo-Daro; G = Ganweriwala; H = Harappa; K = Kalibangan; R = Rakhigarhi. (B) Late Harappan (red) and Painted Gray Ware (white) sites.
Fig. 4.
Fig. 4.
Palaeo-hydroclimate reconstructions and sedimentary activity chronology for the Harappan domain. (A) Indian monsoon precipitation reconstruction (35). (B) Synthetic reconstructions for the Indian monsoon domain (black) and westerly precipitation (37) (gray). (C) Sedimentation ages for fluvial forms in: Sindh (i.e., Indus fluvial mega-ridge); Nara Valley; Indus-Panjnad-Ghaggar-Hakra confluence; Punjab incised valleys; Punjab interfluves (doabs); and the lower and upper Ghaggar-Hakra (G-H) system regions, respectively. OSL dates are represented by triangles and calibrated AMS radiocarbon dates by circles; error bars are shown if larger than the symbol size. Fluvial deposits are shown in black- and white-filled symbols (for high vs. low sedimentation rate deposits, respectively), whereas dunes are represented by gray-filled symbols. Ages for the upper Ghaggar-Hakra system are from Saini et al. (33). The temporal extent of each Harappan phase is indicated by vertical dashed lines (E = early; M = mature; L = late).
Fig. P1.
Fig. P1.
(A) Morphology of the Indo-Gangetic Plain (for altitudes, colors repeat every 10 m to 300 m). Convex downslope, aggradational landscapes have a light mask, whereas incisional landscapes have a red mask. Ghaggar-Hakra and Nara regions are indicated by G-H and N, respectively. Upper inset shows the longitudinal profiles for the Indus and its Punjabi tributaries. Lower inset shows the Harappan domain with modern regions. (B) Early/Mature Harappan sites with major urban centers: D = Dholavira; M = Mohenjo-Daro; G = Ganweriwala; H = Harappa; K = Kalibangan; R = Rakhigarhi. Interfluves are in gray and modern river courses in blue. (C) Late Harappan sites.

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