Tree-ring δ18O records of abating June-July monsoon rainfall over the Himalayan region in the last 273 years

There are knowledge gaps in the long-term changes in Indian summer monsoon rainfall (ISMR, June-September) behaviour, which affects the livelihood of large population in the Indian subcontinent. To better understand ISMR variability, we reconstructed June-July rainfall for the period 1743-2015 CE from Dingad valley, Uttarakhand, central Himalaya using delta O-18 variations in tree rings. For this, regional mean tree-ring isotope chronology, prepared by merging delta O-18 chronologies of two conifer (Abies pindrow (Royle ex D.Don) Royle and Picea smithiana (Wall.) Boiss) and one broadleaf deciduous species (Aesculus indica (Wall. ex Camb.) Hook), was used. The reconstructed rainfall series revealed significant correlations with the observational monsoon records from different regions of India. The most conspicuous feature in our reconstructed series is a decreasing rainfall trend since 1743 CE with the driest period in the late 20th and early 21st centuries, which is consistent with other monsoon rainfall proxies from a large part of the south Asian monsoon region (India, Nepal, Bhutan, Myanmar and Tibet Plateau). Consistency of reconstructed series with instrumental records and proxies from different regions revealed the capture of regional scale rainfall features in our data testifying its utility in understanding ISMR variability in long-term perspective.