NOAA/WDS Paleoclimatology - Mawmluh Cave, India d18O and d13C Data during the Past Millennium

Protracted droughts lasting years to decades constitute severe threats to human welfare across the Indian subcontinent. Such events are, however, rare during the instrumental period (c. since 1871 CE). In contrast, the historic documentary evidence indicates the repeated occurrences of protracted droughts in the region during the pre-instrumental period implying that either the instrumental observations underestimate the full spectrum of monsoon variability, or the historic accounts overestimate the severity and duration of the past droughts. Here we present a temporally precise speleothem-based oxygen isotope reconstruction of the Indian summer monsoon precipitation variability from Mawmluh cave located in Northeast India. Our data reveal that protracted droughts, embedded within multidecadal intervals of reduced monsoon rainfall, frequently occurred over the past millennium. These extreme events are in striking temporal synchrony with the historically documented droughts, famines, mass mortality events, and geopolitical changes in the Indian subcontinent. Our findings necessitate reconsideration of the region’s current water resources, sustainability, and mitigation policies that discount the possibility of protracted droughts in the future.

持续数年至数十年的长期干旱，对印度次大陆全域的人类福祉构成严重威胁。然而，这类事件在约公元1871年开启的仪器观测期内极为罕见。相较之下，历史文献证据表明，在仪器观测前期，该区域曾反复出现长期干旱事件——这一现象意味着两种可能性：要么仪器观测资料低估了季风变率的完整频谱，要么历史记载高估了过往干旱的严重程度与持续时长。本研究依托印度东北部马姆鲁赫（Mawmluh）洞穴的石笋（speleothem）样品，构建了时间分辨率极高的氧同位素序列，用以重建印度夏季风降水的变率特征。研究数据显示，在过去千年间，嵌入在数十年季风降水偏少时段内的长期干旱事件频发。这些极端干旱事件与印度次大陆历史文献记载的干旱、饥荒、大规模人口死亡事件及地缘政治变革，呈现出显著的时间同步性。本研究结果表明，当前该区域的水资源管理、可持续发展与减灾政策均忽视了未来发生长期干旱的可能性，因此亟需对这些政策进行重新审视。