Tree-rings reconstruct the South Asian summer monsoon index over the last millennium

Research Policy Office
Tuesday 9 December 2014

The South Asian summer monsoon (SASM) is a major atmospheric synoptic climate system affecting nearly a quarter of the human population. Dr Rob Wilson, Department of Earth and Environmental Sciences, with co-authors from China have published a 1000-year-long reconstruction of SASM in the Nature Group journal Scientific Reports.

They utilised 15 tree-ring chronologies to reconstruct the SASM index over the last millennium. The record generated is significantly correlated (r=0.7, p<0.01) with the instrumental SASMI record on annual timescales; this correlation is higher than that obtained in any previous study. The reconstructed SASMI captures 18 of 26 (69%) recorded historical famine events in India over the last millennium; notably, 11 of 16 short events with durations of 1–3 years are accurately depicted in the reconstruction. Moreover, the reconstructed SASMI is positively correlated with variations in total solar irradiance (TSI) on multi-decadal timescales implying that variations in solar activity may influence the SASM. Epoch analysis additionallyindicates that volcanic events may also drive some of the SASM variability about 2 years after major eruptions.

Figure: Time series of the reconstructed South Asian summer monsoon index (SASMI) and total solar irradiance (TSI) over the last millennium.

Shi, F., Li, J., and Wilson, R. 2014. A tree-ring reconstruction of the South Asian summer monsoon index over the past millennium. Scientific Reports, 4 (6739). DOI: 10.1038/srep06739.

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