Climate change, water stress and agriculture in the Indus Civilisation, 3000-1500 BC

This thesis investigates the relationship between climate, agriculture and social change in South Asia's Bronze Age urban Indus Civilisation. Specifically, my research tests the hypothesis that an abrupt weakening of the Indian Summer Monsoon ca 2100 cal BC led to increasing crop water stress, and hence potentially contributed to the Civilisation's decline by reducing food supply. This hypothesis is frequently invoked in discussions of the Civilisation's end, yet until now, has not been empirically tested.

Using material excavated from several Indus settlements, this study uses a novel combination of isotopic techniques to directly test the connection between climate change and agricultural stress. These techniques are first, oxygen isotope analysis of faunal bones and teeth; and second, stable carbon isotope analysis of crop remains. The oxygen analyses provide detailed records of monsoon intensity at a local, human scale, while the carbon analyses provide an empirical test of whether crop water stress increased. Applied in parallel across a diverse suite of Indus sites, these techniques together provide an archaeologically and ecologically-nuanced analysis of climatic impacts. The archaeological analyses are supported by a methodological study, which investigates how water status relates to the stable carbon isotope signature in bar- ley (Hordeum vulgare) and the Indian jujube (Ziziphus mauritiana) along a climatic transect in north-western India today.

Overall, the isotopic results suggest that at the sites sampled here, climate change probably had minimal impacts on crop water availability. This does not necessarily mean that climate change had no impacts on agriculture across the greater Indus sphere, and indeed there are hints that there may have been climatic stress in more vulnerable settings. However, at the sites studied here, any hydrological consequences of climate change-including the 4.2 ka event-appear to have had neither a lasting nor a pervasive impact on the adequacy of crop water supply. This is an important finding, and necessitates a clear refinement of how we think about climatic sensitivity, climatic vulnerability, and climatic impacts across-and indeed beyond-the greater Indus.