Annual and seasonal rainfall variability in Mozambique during the nineteenth century

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Original abstract

Understanding long-term rainfall variability is critical for assessing climate risk in drought-prone regions of southern Africa, yet instrumental records for much of the subcontinent are short and spatially sparse. Here, we present the first annually and seasonally resolved rainfall reconstructions for Mozambique spanning 1817-1900, derived from over 5,700 documentary observations collected across 21 archival repositories in Africa, Europe and North America. Using a structured, multi-source classification framework with explicit confidence ratings, rainfall variability is reconstructed for three homogeneous rainfall zones. The results reveal pronounced spatial and temporal variability in nineteenth century rainfall, but with a strong coherence between the rainfall series for the central and southern zones. Multi-year droughts are identified from 1824-35, 1857-59, 1861-63, 1871-78, 1884-87 and 1893-98, each exhibiting complex regional expressions in their onset, duration and impacts. Extremely wet rainy seasons are reconstructed in 1818-19, 1839-40, 1854-55, 1860-61, 1865-66, 1870-71, 1872-73 and 1898-99. Seasonal analysis demonstrates that intra-annual variability was a critical determinant of annual conditions, challenging interpretations based solely on annual totals. Comparison with early instrumental data indicates broad agreement in reconstructed variability while highlighting expected discrepancies associated with spatial rainfall heterogeneity. Analysis of ENSO-rainfall relationships shows that, although El Niño events were often associated with drier conditions in central and southern Mozambique during the nineteenth century, teleconnections were nonlinear, with no consistent wet signal following La Niña events. This suggests potential non-stationarity in large-scale climate-rainfall relationships relative to the instrumental period. The results from this study provide a rare, seasonally resolved, empirical baseline for evaluating recent extremes, testing climate model simulations, and understanding climate dynamics in the southwest Indian Ocean region. They also demonstrate the value of incorporating Portuguese-language materials into documentary-based rainfall reconstructions, thereby remedying a long-standing linguistic bias in global historical climatological investigations.

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