The Indus valley and adjacent regions are dominated by two major weather systems, the winter cyclonic system of the western highlands and the summer monsoon system of the peninsular subcontinent. The winter cyclonic system produces snowfall in Baluchistan and rainfall in parts of the Indus valley. The summer monsoon brings scattered rainfall to Sindh and Gujarat and heavy rainfall to the northern Indus plain, with rain and snow in the high mountains in the north. These two systems overlap in the Indus valley and if one system fails the other usually provides sufficient precipitation to support large populations throughout the region. The main crop cycles in the Indus valley region are aligned with the winter rains and the summer monsoon rains.
Recent models of global climate indicate that, at 18 000-9000 BP, southern Asia would have been cooler and drier than today, with a weak summer monsoon. From 9000 to 7000 BP, there appears to have been a stronger summer monsoon, warmer summers, and cooler winters. Although these models work at the macrolevel, they cannot be confirmed through detailed analysis of specific sites or regions. Generally speaking, there is no evidence for major changes in climate or rainfall since at least 9000 BP. Specific regional environmental changes that directly impacted human settlement in the greater Indus region can generally be attributed to changing river-flow patterns and humanly induced erosion or soil degradation.
World History
