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

青铜器时代的哈拉帕文明（距今4800-3500年）是世界上最早的大型复杂社会之一，随着在印度西北部和巴基斯坦的大片地区发展出复杂的城市中心网络，哈拉帕文明达到了顶峰。哈拉帕文化的繁盛期在公元前3900年结束，当时主要的城市中心被遗弃，社会经济向以村庄为基础的生活发生了深刻的转变。人们提出了许多假说来解释这一过程，从敌人的入侵到灾难性的洪水、气候变化、印度夏季季风强度的突然下降，以及由于构造活动导致的河道变化。古气候研究表明，哈拉帕文明的大致时期是季风强度下降的时期，其间不时出现干旱。然而，我们缺乏关于印度西北部平原过去环境条件的可靠信息，特别是全新世夏季和冬季的降雨模式。我们建议使用从古里瓦萨湖（印度西北部的一个干涸的playa湖）获得的沉积物岩心来重建过去的降雨变化，并评估气候环境变化与城市哈拉帕文明之间的可能联系。具体来说，我们将测量Riwas岩心中生物成因和自生方解石的氧同位素（18O/16O），以获得哈拉潘地区全新世当地古气候变化的第一个高分辨率代用记录。一个详细的放射性碳年表将为里瓦萨岩心开发，以检查人类-气候-环境的相互作用。城市哈拉帕文明衰落的可能性是水资源变化的结果，这与当前和未来的全球变化和印度人口稠密的冲积平原上的水管理问题有着重大的共鸣。

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.