Spatial and temporal variability of East African Kiremt season precipitation and large-scale teleconnections

摘要

Precipitation during the Ethiopian Kiremt (June-September) season has exhibited significant interannual and multi-decadal variability over the 20th and early 21st century. We investigate the temporal variability in the strength of the teleconnections between sea-surface temperatures in key global oceanic regions, including the Tropical Pacific, Indian Ocean, and Tropical Atlantic, and Kiremt season precipitation at sub-seasonal, interannual and multi-decadal time scales. We also investigate the influence of the Madden-Julian Oscillation (MJO). We perform a systematic analysis of 112-year long (1901-2012) precipitation in the northern region of East Africa including the southern and central regions of Ethiopia and uncover interesting spatial, temporal and sub-seasonal variability, and teleconnection patterns. Precipitation anomalies during wet and dry years extend throughout Northern Africa and also, during September extends over Indian subcontinent, suggesting large-scale variability of wet/dry patterns. Wet (dry) years are accompanied by La Nina like (El Nino like) conditions in the tropical Pacific and extending into Atlantic and Indian Oceans. Through Bayesian dynamical linear modelling we find that temporal changes in seasonal precipitation correspond to changes in the strengths of sea surface temperature teleconnections, and that the relative strengths of these teleconnections rather than one dominant teleconnection influences precipitation variability. During three precipitation epochs in this region, the mid-century pluvial, the late-century drought, and the early 21st century, we find that changes in precipitation are related to changes in the main dynamical features of precipitation. These findings suggest that Kiremt season precipitation is in a new regime, and is of key interest to the agricultural and water resources communities who rely on accurate forecasts of precipitation to make operational decisions.