New Study Suggests Indus Valley Civilization Ended Due to a 200-year drought

A new study suggests that Indus Valley Civilization collapsed and ended due to a 200-year drought which began around 2000 BC. Paleoclimatologists claim that the severe drought was the result of non arrival of monsoon rains. People abandoned well planned cities and this led to the end of the Indus Valley and Harappan civilization.
Scientific American writes 
Based on isotope data from the sediment of an ancient lake, the researchers suggest that the monsoon cycle, which is vital to the livelihood of all of South Asia, essentially stopped there for as long as two centuries. 
The link between this gradual decline and climate has been tenuous because of a dearth of climate records from the region. So Yama Dixit, a paleoclimatologist at the University of Cambridge, UK, and her colleagues examined sediments from Kotla Dahar, an ancient lake near the northeastern edge of the Indus Valley area in Haryana, India, that still seasonally floods. 
Kotla Dahar is a closed basin, filled only by rain and runoff and without outlets. Thus precipitation and evaporation alone determine its water volume. During drought, oxygen-16, which is lighter than oxygen-18, evaporates faster, so that the remaining water in the lake and, consequently, the snails' shells, become enriched with oxygen-18. The team's reconstruction showed a spike in the relative amount of oxygen-18 between 4,200 and 4,000 years ago. This suggests that precipitation dramatically decreased during that time. Moreover, their data suggests that the regular summer monsoons stopped for some 200 years.