Abstract

Contextually, precipitation fluctuated due to climate variability and evolved due to emissions of anthropogenic greenhouse gases and land-use changes since the industrial revolution in the 1880s. However, some studies problematize that there is little understanding of nexuses between precipitation changes and climate change and variability in tropical Africa. Therefore, this paper sought to assess such linkages in semi-arid lowlands of Mwanga District, Tanzania. The findings revealed statistically significant decrease of annual rainfall, Kendall’s tau r_τ (44) = -.230, p = .019 and Kendall’s tau r_τ (39) = -.223, p = .024, at Same Meteorological station (1970 to 2009 and 2012 and 2015) and Nyumba ya Mungu Meteorological stations (1977 to 2015), respectively; thus confirming occurrence of human-induced climate change in the study area. Also, the findings revealed statistically significant correlations between amounts of rainfall (September – February) and Niño 3.4 index and between amounts of rainfall (October – December) and dipole mode index at both stations, hence confirming that precipitation changes during short rainy seasons (Vuli) in the lowlands were significantly influenced by cycles of El Niño-southern oscillation and Indian Ocean dipole. Besides, branched and isoprenoid tetraether (BIT) indices revealed that wettest conditions, due to climate variability. This occurred from 650 to 950 CE (common era), 1550 to 1700 CE, 22 to 25 ka BP (before present, present defined as 1950). Whereas, driest conditions occurred from 1968 to 1974, 1780 to 1820 CE, 1170 to 1300 CE (between ca. 0.8 and 0.6 ka BP), 11.7 to 13.1 (the Younger Dryas), 15 to 18 (Heinrich 1 stadial) and 23.4 (Heinrich 2 stadial) ka BP.  Lastly, the paper recommends enhancement of traditional and modern-day environmental knowledge systems with regard to weather forecasting and prediction.

Key words: Branched and isoprenoid tetraether index, climate change, climate variability, El Niño-southern oscillation, Indian Ocean dipole, and short rainy season.