NOAA/WDS Paleoclimatology - Northwest Himalaya 400 Year Standardized Precipitation Index Reconstruction

Droughts are recurring phenomena in the north-western Himalaya causing severe socio-economic hardships. Our understanding on temporal and spatial occurrence of such extreme droughts in long-term perspective is constrained due to limited short-term weather records. Towards fulfilling such a large data void we developed a network of ring-width chronologies of Himalayan cedar from seven moisture stressed high elevation sites in Kishtwar, Jammu and Kashmir. Moisture responsive ring-width chronologies were used to develop the annual Standardized Precipitation Index (SPI from previous year June to current year May (SPI12-May)) extending back to AD 1613. The SPI reconstruction revealed annual to decadal-scale variability in droughts, which strikingly were more frequent and of larger magnitude during AD 1760s-2017 in comparison to the earlier part of the reconstruction (AD 1613-1750s). Our SPI12-May record revealed strong consistency with other tree-ring-based hydrological records from the western Himalaya. Spatial correlation analyses revealed strong linkage of the SPI with Tropical Pacific Ocean surface temperature.

干旱是喜马拉雅西北部的周期性自然现象，会引发严重的社会经济困境。受限于短期气象观测记录的匮乏，我们对这类极端干旱事件的长期时空分布规律的认知仍存在显著局限。为填补这一重大数据空白，我们在查谟和克什米尔（Jammu and Kashmir）基什特瓦尔（Kishtwar）地区的7个受水分胁迫的高海拔站点，构建了喜马拉雅雪松的树轮宽度年表（ring-width chronologies）网络。利用对水分响应敏感的树轮宽度年表，我们重建了可追溯至公元1613年的年度标准化降水指数（Standardized Precipitation Index, SPI），其时间跨度为前一年6月至当年5月（记为SPI12-May）。该SPI重建结果揭示了干旱事件在年际至年代际尺度上的变异性；尤为显著的是，与重建序列前期（公元1613年至1750年代）相比，公元1760年代至2017年期间的干旱事件发生更为频繁，强度也更高。我们的SPI12-May记录与喜马拉雅西部其他基于树轮的水文记录具有高度一致性。空间相关性分析表明，该标准化降水指数与热带太平洋海表温度存在显著关联。