Holocene Palaeoclimate history of Lake Riwasa: Implications for the urban Harappan Civilization

The Bronze Age Harappan Civilisation (4800-3500 BP) was one of the world's first great complex societies and attained its peak with the development of a network of sophisticated urban centres spread over an extensive tract of NW India and Pakistan. The Harappan cultural florescence ended by 3900 BP when major urban centres were abandoned and there was a profound socio-economic shift towards village based life. Many hypotheses have been put forward to explain this process, ranging from enemy invasion, to catastrophic floods, climate change, an abrupt decline in the strength of the Indian summer monsoon, and shifts of river courses due to tectonic activity. Palaeoclimate studies suggest that the approximate time of the Harappan Civilisation was a period of declining monsoon strength, punctuated by episodes of aridity. However, we lack reliable information about past environmental conditions on the plains of NW India, particularly the summer and winter rainfall patterns during the Holocene. We propose to use sediment cores obtained from palaeo-Lake Riwasa, a dry playa lake in NW India, to reconstruct past changes in rainfall and assess possible connections between climate-environment changes and the urban Harappan Civilisation. Specifically, we will measure oxygen isotopes (18O/16O) of biogenic and authigenic calcite from the Riwas cores to produce the first high-resolution, proxy record of local palaeoclimate change for the Holocene obtained directly from the Harappan region. A detailed radiocarbon chronology will be developed for the Riwasa cores to examine human-climate-environment interactions. The possibility that the urban Harappan civilisation declined as a consequence of changes to water resources has significant resonance with current and future issues of global change and water management on the heavily populated alluvial plains of India.