Tree-ring reconstructed rainfall variability in Zimbabwe

Abstract

We present the first tree-ring reconstruction of rainfall in tropical Africa using a 200-year regional chronology based on samples of Pterocarpus angolensis from Zimbabwe. The regional chronology is significantly correlated with summer rainfall (November–February) from 1901 to 1948, and the derived reconstruction explains 46% of the instrumental rainfall variance during this period. The reconstruction is well correlated with indices of the El Nino-southern oscillation (ENSO), and national maize yields. An aridity trend in instrumental rainfall beginning in about 1960 is partially reproduced in the reconstruction, and similar trends are evident in the nineteenth century. A decadal-scale drought reconstructed from 1882 to 1896 matches the most severe sustained drought during the instrumental period (1989–1995), and is confirmed in part by documentary evidence. An even more severe drought is indicated from 1859 to 1868 in both the tree-ring and documentary data, but its true magnitude is uncertain. A 6-year wet period at the turn of the nineteenth century (1897–1902) exceeds any wet episode during the instrumental era. The reconstruction exhibits spectral power at ENSO, decadal and multi-decadal frequencies. Composite analysis of global sea surface temperature during unusually wet and dry years also suggests a linkage between reconstructed rainfall and ENSO.