The three river-valley civilizations discussed in this chapter were located in arid or semiarid regions. Such regions are particularly vulnerable to changes in the environment. Scholars' debates about the existence and impact of changes in the climate and landscape of the Indus Valley illuminate some of the possible factors at work, as well as the difficulties of verifying and interpreting such long-ago changes.
One of the points at issue is climatic change. An earlier generation of scholars believed that the climate of the Indus Valley was considerably wetter during the height of that civilization than it is now. As evidence, they cited the enormous quantities of timber, cut from extensive forests, that would have been needed to bake the millions of mud bricks used to construct the cities (see photo), the distribution of human settlements on land that is now unfavorable for agriculture, and the representation of jungle and marsh animals on decorated seals. This approach assumes that the growth of population, prosperity, and complexity in the Indus Valley in the third millennium B. C.E. required wet conditions, and it concludes that the change to a drier climate in the early second millennium b. c.e. pushed this civilization into decline.
Other experts, skeptical about radical climate change, countered with alternative calculations of the amount of timber needed and evidence of plant remains—particularly barley, a grain that is tolerant of dry conditions. However, recent studies of the stabilization of sand dunes, which occurs in periods of heavy rainfall, and analysis of the sediment deposited by rivers and winds have been used to strengthen the claim that the Indus Valley used to be wetter and that in the early - to mid-second millennium B. C.E. it entered a period of relatively dry conditions that have persisted to the present.
A much clearer case can be made for changes in the landscape caused by shifts in the courses of rivers. These shifts are due, in many cases, to tectonic forces such as earthquakes. Dry channels, whether detected in satellite photographs or by on-the-ground inspection, reveal the location of old riverbeds, and it appears that a second major river system, the Hakra, once ran parallel to the Indus some distance to the east. The Hakra, with teeming towns and fertile fields along its banks, appears to have been a second axis of this civilization. Either the Sutlej, which now feeds into the Indus, or the Yamuna, which now pours into the Ganges, may have been the main source of water for this long-gone system before undergoing a change of course. The consequences of the drying-up of this major waterway must have been immense—the loss of huge amounts of arable land and the food that it produced, the abandonment of cities and villages and consequent migration of their populations, shifts in the trade routes, and desperate competition for shrinking resources.
As for the Indus itself, the present-day course of the lower reaches of the river has shifted 100 miles (161 kilometers) to the west since the arrival of the Greek conqueror Alexander the Great in the late fourth century b. c.e., and the deposit of massive volumes of silt has pushed the mouth of the river 50 miles (80 kilometers) farther south. Such a shift of the riverbed and buildup of alluvial deposits also may have occurred in the third and second millennia b. c.e.
A recent study concludes: “It is obvious that ecological stresses, caused both climatically and technically, played an important role in the life and decay" of the Indus civilization.
Source: Quotation from D. P. Agarwal and R. K. Sood, in Harappan Civilization:A Contemporary Perspective, ed. Gregory L. Possehl (Warminster, England: Aris and Phillips, 1982), 229.
World History
