Amazing stuff! Do severe droughts coincide with warming climate? Maybe besides the well known Medieval Warm Period there were other significant Warm Periods over the past 5,000 years or further back.
Despite all this hysteria and alarmism about climate change since 1970s one would assume the question of the influence of climate change on this early civilization would be raised. Not really or not very satisfactory.
There is too much reference given to today's climate conditions like AMO [Atlantic Multidecadal Oscillation] and El Ninja! I don't buy it. These researchers also relied on climate models. They are dubious. The abstract of the research article narrowly mentions "hydroclimatic variations". But what causes hydroclimatic variations like severe, large geographic area and prolonged droughts?
"The culprit behind the mysterious disappearance of one of the most advanced urban civilizations at the time, contemporaries to Mesopotamians and Egyptians, has finally been identified: a series of severe, long-lasting droughts that dried rivers across the Indus Valley more than 4,000 years ago.
A study ... reveals that these dry spells likely pushed communities to move, change crops, and fundamentally reorganize their civilization.
“The most surprising finding is that the Harappan decline was driven not by a single catastrophic event, but by repeated, long, and intensifying river droughts lasting centuries,” ...
The Indus Valley Civilization, also known as the Harappan empire, rose to prominence around 5,000 years ago along the fertile plains of northwest India and Pakistan. During its mature period, the society developed well-planned cities with grid systems of roads, advanced water management, sophisticated drainage, and large granaries. The Harappan were also among the first to cultivate and process cotton.
But around 3,900 years ago, things started falling apart and cities emptied out. ...
Now, a team of scientists ... blended evidence from lake sediments, cave deposits, and other natural archives with high-tech climate models to reconstruct how water moved through the Indus basin around 3,000 years ago. The team found that the decline was not due to a single drought, but a sequence of four major droughts. Researchers dubbed these four events D1, D2, D3 and D4.
Hiren told New Atlas that the most severe droughts were D2 and D3, which lasted between 102 and 164 years, impacting over 90% of the Indus Valley region during the transition from the mature to the late Harappan period. ...
But what flipped the climatic conditions? ... the Pacific and North Atlantic oceans influencing the Indian monsoon through large-scale atmospheric “teleconnections.” When the Pacific warms in an El Niño–like pattern, it weakens the monsoon circulation and reduces summer rainfall over South Asia. At the same time, a cooler North Atlantic (negative AMO phase) suppresses moisture transport into the monsoon system. It shifts atmospheric pressure patterns, further weakening the monsoon. ..."
From the abstract:
"Hydroclimatic variations are among the factors shaping the rise and fall of the Indus Valley Civilization. Yet, constraining the role of water availability across this vast region has remained challenging owing to the scarcity of site-specific paleoclimate records.
By integrating high-resolution paleoclimate archives with palaeohydrological reconstructions from transient climate simulations, we identify the likelihood of severe and persistent river droughts, lasting from decades to centuries, that affected the Indus basin between ~4400 and 3400 years before present.
Basin-scale streamflow anomalies further indicate that protracted river drought coincided with regional rainfall deficits, together reducing freshwater availability. We contend that reduced water availability, accompanied by substantially drier conditions, may have led to population dispersal from major Harappan centers, while acknowledging that societal transformation was shaped by a complex interplay of climatic, social, and economic pressures."
By integrating high-resolution paleoclimate archives with palaeohydrological reconstructions from transient climate simulations, we identify the likelihood of severe and persistent river droughts, lasting from decades to centuries, that affected the Indus basin between ~4400 and 3400 years before present.
Basin-scale streamflow anomalies further indicate that protracted river drought coincided with regional rainfall deficits, together reducing freshwater availability. We contend that reduced water availability, accompanied by substantially drier conditions, may have led to population dispersal from major Harappan centers, while acknowledging that societal transformation was shaped by a complex interplay of climatic, social, and economic pressures."
River drought forcing of the Harappan metamorphosis (open access)
Fig. 1: Rainfall variability over Indus Valley Civilization area from 6000 years BP to present (1850 CE).
Fig. 2: Identification of major drought events during Harappan timeframe and corresponding changes in paleoclimate variables.
