Nowadays it appears that monsoonal rivers gradually dried in the Indus Valley around 1900 BCE and that this was a major cause for the decline of the Indus civilization:
Giosan, Liviu, Peter D. Clift, Mark G. Macklin, Dorian Q. Fuller, Stefan Constantinescu, Julie A. Durcan, Thomas Stevens, Geoff A. T. Duller, Ali R. Tabrez, Kavita Gangal, Ronojoy Adhikari, Anwar Alizai, Florin Filip, Sam VanLaningham, and James P. M. Syvitski, 2012. Fluvial landscapes of the Harappan civilization. Proceedings of the National Academy of Sciences of the United States of America 109 (22), 29 May 2012, doi: 10.1073/pnas.1112743109.
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.
Giosan, Liviu, William D. Orsi, Marco Coolen, Cornelia Wuchter, Ann G. Dunlea, Kaustubh Thirumalai, Samuel E. Munoz, Peter D. Clift, Jeffrey P. Donnelly, Valier Galy, Dorian Q. Fuller, 2018. Neoglacial climate anomalies and the Harappan metamorphosis. Climate of the Past: Discussions.
https://doi.org/10.5194/cp-2018-37 Abstract: We show that strong winter monsoons between ca. 4,500 and 3,000 years ago occurred during an interval of weak interhemispheric temperature contrast, which we identify as the Early Neoglacial Anomaly (ENA), and were accompanied by changes in wind and precipitation patterns across the eastern Northern Hemisphere and Tropics. This coordinated climate reorganization may have helped trigger the metamorphosis of the urban Harappan civilization into a rural society through a push-pull migration from summer flood-deficient river valleys to the Himalayan piedmont plains with augmented winter rains. Finally, we speculate that time transgressive landcover changes due to aridification of the Tropics may have led to a generalized instability of the global climate during ENA at the transition from the warmer Holocene Optimum to the cooler Neoglacial.
The 30 feet of flood silt at Mohenjo-daro as “flood evidence” was discussed in the 1960s & 1970s:
Raikes, Robert L., & Robert H. Dyson, Jr., 1961. The prehistoric climate of Baluchistan and the Indus Valley. American Anthropologist 63: 265-281. Reprinted in: G. L. Possehl (ed.), Ancient cities of the Indus, 1979, pp. 223-233.
Raikes, Robert L., 1964. The end of the ancient cities of the Indus. American Anthropologist 66.2: 284-299. Reprinted in: G. L. Possehl (ed.), Ancient cities of the Indus, 1979, pp. 297-306.
Raikes, Robert L., 1965. The Mohenjo-daro floods. Antiquity 39: 196-203.
Dales, George F., 1966. The decline of the Harappans. Scientific American 241(5): 92-100. Reprinted in: G. L. Possehl (ed.), Ancient cities of the Indus, 1979, pp.307-312.
Raikes, Robert L., 1967. The Mohenjo-daro floods — further notes. Antiquity 41: 64-66.
Lambrick, H. T., 1967. The Indus Flood Plain and the “Indus” Civilization. Geographical Journal 133 (4): 483-495. Reprinted in: G. L. Possehl (ed.), Ancient cities of the Indus, 1979, pp. 313-322.
Dales, George F., & R. L. Raikes, 1968. The Mohenjo-daro floods: A rejoinder. American Anthropologist 70 (5): 957-961.
Raikes, Robert L., & George F. Dales, 1977. The Mohenjo-Daro floods reconsidered. Journal of the Palaeontological Society of India 20: 251-260.
Raikes, Robert L., 1979. The Mohenjo-daro bfloods: the cdebate continues. Pp. 561-566 in: M. Taddei (ed.), South Asian Archaeology 1977. Neples.
Best wishes, Asko Parpola
This question occurred to me recently. Does the massive flooding that Pakistan recently experienced give us some possibilities about the demise of the Indus Civilization? Are there any indications of such massive floods in Indus archaeology? I would appreciate any suggestions for reading on this topic. Best regards,
Madhav M. Deshpande
Professor Emeritus, Sanskrit and Linguistics
University of Michigan, Ann Arbor, Michigan, USA
Senior Fellow, Oxford Center for Hindu Studies
Adjunct Professor, National Institute of Advanced Studies, Bangalore, India
[Residence: Campbell, California, USA]
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