Abstract 131

Abstract ID: 131

Characterization of Intra-Seasonal Variability during Extreme Dry Seasons over the Greater Horn of Africa (GHA): Implications for Climate Adaptation and Mitigation

Lead Author: Vincent Owanda Otieno
Technical University of Kenya, Kenya

Keywords: Rainfall Onset & Cessation, Drought, SST-forcing, Convective band, Greater Horn of Africa

Abstract: Better understanding of intra-seasonal rainfall characteristics is crucial for farming, most of which is rain-fed in Africa, water resource management and many other use. NCEP reanalysis data which was validated against Era-Iterim and CHIRP and found able to reproduce intra-seasonal variability of precipitation is the main data set used in this study. Using cumulative time plots to assess the onset, intra-seasonal variation and cessation of seasonal rainfall during the dry periods of 1998/9, 2010/1, 2020/1 and 2021/2 we found that the onset of rainfall events during OND seasons is slow, dragging up to the second week of the season during the extreme dry periods. This late onset, coupled with breaks between the seasons and early withdrawal, shortened the season to about 5 – 6 weeks. Unlike in other seasons the onset during OND was coherent across the years. The severe drought conditions witnessed during OND and JF period are largely due to global SSTs: due to cold temperature anomalies over central pacific and large scale warming over the Indo-Pacific region coupled with a descending arm of walker circulation which depressed convective activities over Indian Ocean. MAM precipitation variation over the region is largely due to synoptic scale systems triggered by westerly wind anomalies. The failure of MAM season over equatorial GHA region during 2011 and 2021 was largely due to moderately warm temperatures over the western pacific/Sumatra region and warm Indian Ocean temperature over the south in addition to strong upper level divergent wind and descending arm of the walker circulation over Indian Ocean. The warming over southern Indian Ocean expanded northward as cold SSTs over the Arabian Sea stretched on the east coast of the Horn of Africa and west coast of Indian sub-continent forming an asymmetric V-shaped pattern of cold northern Indian Ocean SSTs sandwiching the creeping warm SSTs from the southern Indian Ocean. This temperature pattern orientation slowed the transition of convective band from the Southern Africa region towards the north delaying the onset of MAM season over equatorial region. understanding these dynamics is crusial in predictability especially for the extreme dry climatic seasons.

Lydia Gachahi (Technical University of Kenya, Department of Geoscience and Environment, Nairobi, Kenya)
Masilin Gudoshava (IGAD Climate Prediction and Applications Centre, Nairobi, Kenya)
Herbert O Misiani (IGAD Climate Prediction and Applications Centre, Nairobi, Kenya)