Shifting Patterns of Ethiopian MAM Rainfall: Effects of Sea Surface Temperature and Atmospheric Circulation (1981–2022)

Abstract

Understanding seasonal rainfall patterns and variability is crucial for managing water resources, pastoral and agricultural activities in Ethiopia, an especially climate-vulnerable country. This study examines trends in March–April–May (MAM) rainfall from 1981 to 2022, emphasising the relationships between climate indices, atmospheric circulation patterns, and variations in precipitation. By utilising daily CHIRPS rainfall data and monthly sea surface temperature (SST), sea level pressure (SLP) and other reanalysis datasets, we applied extreme indices analysis, correlation analysis and Student's t-tests to compare climate factors and rainfall during two distinct periods 1(981–2001 and 2002–2022) and assess changes relative to the 1991–2020 long-term mean. Our findings reveal a notable shift towards warmer sea surface temperature (SST) phases in key ocean basins, with significant positive correlations (r > 0.45, p < 0.05) between Ethiopian MAM rainfall and SSTs in the Mediterranean, Northwest Pacific, Northern Atlantic and Western Indian Ocean. Precipitation patterns shifted from above-average to below-average rainfall, aligning with opposite trends in the tropical central Indian Ocean. A long-term trend analysis revealed a marked decrease in rainy days across northeast, east, central, south and southeastern Ethiopia during 2002–2022, with an increase in consecutive dry days and a decrease in consecutive wet days, with statistical significance at the 95% confidence level. The period from 2002 to 2022 was characterised by La Niña-like conditions and a negative Pacific Decadal Oscillation, which had a considerable impact on rainfall patterns. Changes in large-scale atmospheric circulation reduced moisture transport to Ethiopia, leading to drier conditions. These findings enhance our understanding of Ethiopian rainfall variability and its drivers, crucial for improving early warning systems and developing climate adaptation strategies in the region.