Abstract
The coast of central East Africa (CEA) is a dynamic region in terms of climate, in which fisheries and marine-related services impact a large portion of the population. The main driver of regional dynamics is the seasonal alternation of the Northeast (NE) and Southeast (SE) monsoons. Winds associated with these monsoons modulate the prevalent, remotely-forced East African Coastal Current (EACC). Here, present and future trends in winds and sea surface temperature (SST) of the CEA and adjacent regions are investigated using reanalysis and reconstructed data, and an ensemble of General Circulation Models. It was found that the winds and SST show unidirectional trends, with magnitude and spatial differences between the NE and SE monsoons. Winds show weakening trends during the NE monsoon, in the past and future, of the Somali region; with no significant trends during the SE monsoon. SST shows increasing trends in the entire region in the past and future, with stronger warming during the NE monsoon off Somalia; SST trends are smaller in the CEA. These trends could impact the CEA through increased water-column stability and decreased upwelling due to shifting of the EACC separation from the continent. However, given the coarse resolution of data analyzed, regional modeling is still necessary to understand the impacts on local dynamics and productivity in the CEA.
Highlights
The region encompassing the coasts of Kenya and Tanzania and their islands, referred to here as Central East Africa (CEA), is a highly dynamic, remotely forced coastal region
The CEA is embedded in the northward East African Coastal Current (EACC), which is the northward extension of the South Equatorial Current (SEC) that passes the northern tip of Madagascar before reaching the African continent (Schott and McCreary, 2001; Manyilizu et al, 2016); the strength of the EACC and the CEA regional climate depend on the seasonal shift in the Inter-Tropical Convergence Zone that drives the Northeast (NE) and Southeast (SE) monsoons (McClanahan, 1988)
Wind, the physical feature that experiences the largest variability during the year, shows significant trends only in the zonal component off the eastern side of the Somalia jet during the NE monsoon – a region with weak or zero zonal wind in the climatology
Summary
The region encompassing the coasts of Kenya and Tanzania and their islands, referred to here as Central East Africa (CEA), is a highly dynamic, remotely forced coastal region. Mahongo | WIO Journal of Marine Science Special Issue 1 / 2020 63-70 past trends, wind vectors from 20th Century Reanalysis V3 (20CR) was obtained from the National Ocean and Atmospheric Administration (NOAA/CIRES/ DOE/ESRL PSD, Boulder, Colorado, USA) available at https://www.esrl.noaa.gov/psd, and SST data from the HadISST1 (HadSST) reconstruction dataset provided by the Meteorological Office Hadley Centre in the UK, available at https://www.metoffice.gov.uk/ hadobs/hadisst/.
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