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 down-stream, 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.
Giosan, L., Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, United States; Clift, P.D., School of Geosciences, University of Aberdeen, Aberdeen AB24 3UE, United Kingdom; Macklin, M.G., Institute of Geography and Earth Sciences, Aberystwyth University, Aberystwyth SY23 3DB, United Kingdom; Fuller, D.Q., Institute of Archaeology, University College London, London WC1H 0PY, United Kingdom; Constantinescu, S., Department of Geography, University of Bucharest, Bucharest, 70709, Romania; Durcan, J.A., Institute of Geography and Earth Sciences, Aberystwyth University, Aberystwyth SY23 3DB, United Kingdom; Stevens, T., Department of Geography, Royal Holloway, University of London, Egham, Surrey TW20 0EX, United Kingdom; Duller, G.A.T., Institute of Geography and Earth Sciences, Aberystwyth University, Aberystwyth SY23 3DB, United Kingdom; Tabrez, A.R., National Institute of Oceanography, Karachi, 75600, Pakistan; Gangal, K., School of Mathematics and Statistics, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom; Adhikari, R., Institute of Mathematical Sciences, Chennai 600 113, India; Alizai, A., School of Geosciences, University of Aberdeen, Aberdeen AB24 3UE, United Kingdom; Filip, F., Department of Geography, University of Bucharest, Bucharest, 70709, Romania; VanLaningham, S., School of Fisheries and Ocean Sciences, University of Alaska, Fairbanks, AK 99775-7220, United States; Syvitski, J.P.M., Community Surface Dynamics Modeling System (CSDMS) Integration Facility, Institute of Arctic and Alpine Research (INSTAAR), University of Colorado, Boulder, CO 80309-0545, United States, Department of Geology and Geophysics, Louisiana State University, Baton Rouge, LA 70803, United States
Recommended Citation:
Giosan L.,Clift P.D.,Macklin M.G.,et al. Fluvial landscapes of the Harappan civilization[J]. Proceedings of the National Academy of Sciences of the United States of America,2012-01-01,109(26)