Spatio-temporal rainfall variability and its linkage with large scale climate oscillations over the Republic of South Sudan

Abstract

Climate change has distorted the rainfall spatio-temporal distribution. Therefore, understanding the spatio-temporal rainfall variation and its causes at meso and micro-level could provide insight for the water and agricultural development interventions. This article examines the spatio-temporal rainfall variability and driving factors in connection with large scale global oscillation. CHIRPS rainfall and NCEP/NCAR wind fields data from 1981 to 2019 were used. Rotaed Emperical Ortogonal Function (REOF) was employed to investigate spatio-temporal rainfall variability. Large scale moisture transport was studied using lower (1000–850 hPa), middle (600–500 hpa), and upper (300–100 hPa) level wind fields. The result reveals that in South Sudan rainfall dominant variance regions were not uniform across seasons. Northern, Southcentral, and Southeastern tip regions were the top three dominant variance regions which explain around 30 %, 25 % and 17 % of the total variation in REOF1, REOF2, and REOF3 during the spring season respectively. Likewise, during the summer season the dominant variance REOF1 (28 %), REOF2 (24 %), and REOF3 (9 %) was observed in South-east, West, and, North-west, whereas; the autumn dominant variance in North-west, North-east, and South-east explain about REOF1 (22.6 %), REOF2 (19.9 %), and REOF3 (16.7 %) of the total variation respectively. The alternative wet and dry years were causing drought and flooding in the study sites. Low-level southeasterly winds from India and over the equator from the Atlantic Ocean carry rain-bearing moisture to South Sudan. The winds converge and convection is triggered by African Easterly and Tropical Easterly jet favors convection during the summer and spring seasons. Sea Surface temperature shows a positive and negative correlation with rainfall variability. Rainfall spatio-temporal assessment is crucial for water resource management, agricultural productivity, and climate change mitigation.