Rainfall Variability over Tanzania during October to December and Its Association with Sea Surface Temperature (SST)

Hassan Khatib Ame,Asya Omar Hmad,Agnes Lawrence Kijazi,Kantamla Biseke Mafuru,Miraji Khamis Miraji,Masoud Makame Faki,Ladislaus Benedict Changa,Mohamed Khamis Ngwali

doi:10.4236/acs.2021.112019

Abstract

The current study examines the interannual rainfall variability and its associated atmospheric circulation in Tanzania during October-December (OND) rainfall season based on 1974 to 2010 climatology. The Empirical Orthogonal Function (EOF), composite and correlation analysis were used in this study. Years with enhanced precipitation are found to be associated with the low level moist and unstable wind from Congo basin which organizes and forms a confluent zone, an inter tropical convergence zone (ITCZ) extending from Congo to northern sector of the country. It however, characterizes low-level westerly moisture flux transport sourced from Congo basin, ascending limb of the local Indian Ocean Walker circulation over East Africa which enhances convection for wetness condition. Wet years are also coupled with the positive Indian Ocean Dipole (IOD) and the warm phase of the El Nino Southern Oscillation (ENSO) condition. On the spatial scale, both the IOD and ENSO indices are well correlated with OND rains over the bimodal areas (Lake Victoria basin, North Eastern Highlands (NEH), and northern coast) with strong correlation being to the NEH. Strong temporal correlation is revealed between the OND rains and IOD (r = 0.6304) compared to ENSO (r = 0.5538) indicating that anomalous warming over the western Indian Ocean has a faster response to OND rains in Tanzania than the remote influence induced by anomalous warming from the central Pacific Ocean. The patterns associated with dry years are found to be linked with the low-level divergence accompanied by convergence in the upper level. This condition enhances continuous descending motion accompanied with suppression in rainfall activities. Dry years are also associated with negative IOD, cold phase of ENSO condition, descending limb of the Walker Circulation and significant reduction in the westerly moisture flux transport sourced from Congo basin towards the western sector and Lake Victoria basin.

Highlights

Understanding the inter-annual variability of rainfall in Tanzania is of crucial importance to all socio-economic sectors, sectors that are very sensitive to climate variability including agriculture, infrastructure, fisheries, hydro-electric power generation and water resources
Both the Indian Ocean Dipole (IOD) and El Nino Southern Oscillation (ENSO) indices are well correlated with OND rains over the bimodal areas (Lake Victoria basin, North Eastern Highlands (NEH), and northern coast) with strong correlation being to the NEH
Strong temporal correlation is revealed between the OND rains and IOD (r = 0.6304) compared to ENSO (r = 0.5538) indicating that anomalous warming over the western Indian Ocean has a faster response to OND rains in Tanzania than the remote influence induced by anomalous warming from the central Pacific Ocean

Summary

Introduction

Understanding the inter-annual variability of rainfall in Tanzania is of crucial importance to all socio-economic sectors, sectors that are very sensitive to climate variability including agriculture, infrastructure, fisheries, hydro-electric power generation and water resources. Rainfall distribution in Tanzania exhibits a stronger spatial and temporal variability characterized by frequent occurrence of extreme events including severe and devastating droughts and floods. The occurrence of these extremes often causes severe consequences to the livelihoods, infrastructure, food insecurity, energy and water shortages, and deaths of human beings and animals [4] [5] [6]. Understanding the trend of rainfall variability helps to generate more understanding about the dynamics and consequence of climate change and variability on environmental and human system [7]. It is well documented that the impact of climate change on agriculture in developing countries has been increasing causing decrease in agricultural production and productivity [8]

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Conclusion