Abstract
Archaeological sites hold important clues to complex climate-human relationships of the past. Human settlements in the peripheral zone of Indus culture (Gujarat, western India) are of considerable importance in the assessment of past monsoon-human-subsistence-culture relationships and their survival thresholds against climatic stress exerted by abrupt changes. During the mature phase of Harappan culture between ~4,600–3,900yrsBP, the ~4,100±100yrsBP time slice is widely recognized as one of the major, abrupt arid-events imprinted innumerous well-dated palaeo records. However, the veracity of this dry event has not been established from any archaeological site representing the Indus (Harappan) culture, and issues concerning timing, changes in subsistence pattern, and the likely causes of eventual abandonment (collapse) continue to be debated. Here we show a significant change in crop-pattern (from barley-wheat based agriculture to ‘drought-resistant’ millet-based crops) at ~4,200 yrs BP, based on abundant macrobotanical remains and C isotopes of soil organic matter (δ13CSOM) in an archaeological site at Khirsara, in the Gujarat state of western India. The crop-change appears to be intentional and was likely used as an adaptation measure in response to deteriorated monsoonal conditions. The ceramic and architectural remains of the site indicate that habitation survived and continued after the ~4,200yrsBP dry climatic phase, but with declined economic prosperity. Switching to millet-based crops initially helped inhabitants to avoid immediate collapse due to climatic stresses, but continued aridity and altered cropping pattern led to a decline in prosperity levels of inhabitants and eventual abandonment of the site at the end of the mature Harappan phase.
Highlights
Archaeological sites in the Kachchh region of Gujarat state of western India, located on the western boundary of monsoonal rainfall falling under semi-arid to arid zone with less than ~60 cm annual rainfall [1], represent the northwestern periphery of the Indus (Harappan) civilization, In contrast to the core regions of Indus (Panjab, Haryana and Jammu regions) that receive higher rainfall during the summer and winter, the Kachchh region is more vulnerable to monsoonal fluctuations and the vagaries of abrupt and extreme climate change
14C dates from all trenches and associated ceramic material suggested that this site can be divided into two phases: the early Phase IA (~4600–4300 yrs BP), and the mature Phase IB (~4100–3900 yrs BP) separated by a Transitional Phase (TP) (~4300–4100 yrs BP)
Our study from the Indus archaeological site at Khirsara (Gujarat, western India) provides compelling evidence for a major change in cropping pattern from barley- based to milletbased crops at ~4,200 yrs BP, suggesting that it was probably the first ever agricultural response to prevailing monsoonal dryness
Summary
Archaeological sites in the Kachchh ( called Kutch) region of Gujarat state of western India, located on the western boundary of monsoonal rainfall falling under semi-arid to arid zone with less than ~60 cm annual rainfall [1], represent the northwestern periphery of the Indus (Harappan) civilization, In contrast to the core regions of Indus (Panjab, Haryana and Jammu regions) that receive higher rainfall during the summer (southwest monsoon) and winter (precipitation brought by westerly winds), the Kachchh region is more vulnerable to monsoonal fluctuations and the vagaries of abrupt and extreme climate change. Available well-dated palaeo records from India, Central Asia, Middle East, and Europe, indicate abrupt and extreme change in climate (monsoon) at ~4,100±100 yrs BP. Increased aridity during this period is considered to be a major factor responsible for collapse of the old kingdom in Egypt, the Akkadian empire in Mesopotamia and Bronze Age societies in Italy, Greece and Crete, and northern Algeria [6,7,8,9,10,11]. There is an ongoing debate regarding the impact of this arid-phase on the Indus (Harappan) Civilization [4, 12, 13]
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