EARLY CIVILISATIONS OF THE NORTHWESTduring this period that the Yamuna river which originally had been flowing
into the Ghaggar river shifted its ancient course to its present course in the
Ganga-Yamuna Doab. The annual flooding of the Ghaggar, the life spring
of the eastern cities of the Harappans, was thus reduced in a dangerous
way. Other scientists have suggested ecological reasons for the decline of
the great civilisation: over-grazing, and deforestation caused by the
operation of innumerable fireplaces and kilns for firing bricks.
Palaeobotanical research in Rajasthan may provide another amazing
explanation of the decline of the Indus civilisation. According to these
findings there was a slight increase of rainfall and vegetation in the Indus
region in the sixth millennium, and during the third millennium there was
a sudden and steep rise in rainfall which reached its peak around 2500
BC. But by the end of the third millennium this rainfall had receded as
rapidly as it had increased, and by about 1800 to 1500 BC it had come
down to a level well below that of 3000 BC. There was another slight
increase of rainfall between 1500 and 1000 BC then it decreased once
more. The period around 400 BC was probably one of the driest periods
of all. Subsequently, rainfall became more abundant but never again
reached the peak which it had attained around 2500 BC. The last 2,000
years up to the present have witnessed a pattern of rainfall and
vegetation in South Asia which conforms to a mean value between the
extremes of 2500 and 400 BC.
It is fascinating to see the course of history in the context of these
findings. The rise and fall of the Indus civilisation could thus have been
strongly influenced by changes in climate, and even the immigration of the
Vedic Aryans and their settlement in the northern Indus region could then
be attributed to the renewed increase of rainfall and vegetation in the
period after 1500 BC. Similarly the decline of the fortunes of the Aryans in
that region after 1000 BC and their movement eastwards into the Ganges
valley could be explained by means of these climatological data. The dry
period would have made the jungles of the Gangetic plains penetrable and
when the climate improved again after 500 BC the migrants would have
already established their footholds along the Ganges and have started
cutting and burning the forest, thus reclaiming fertile lands for agriculture.
The improvement of the climate would then have contributed to the
second wave of urbanisation which started in South Asia at that time. But
only more detailed palaeobotanical research can prove that these
hypotheses derived from the findings in Rajasthan are applicable to other
regions of South Asia as well.
In addition to changes in climate and perhaps an inundation caused by a
tectonic upheaval, there seem also to have been socio-economic factors
which contributed to the decline of the great civilisation. At their height
around 2200 BC, the centres of this civilisation had become far removed
from their agricultural roots and yet they were more dependent than ever