Climate characteristics in Tanzania and its relationship with general circulation and Sea Surface Temperature (SST)
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Date
2012
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Publisher
China University of Geosciences
Abstract
This study was conducted to examine the climate characteristic of southern highland
Tanzania (Latitude 6°S-12°S and Longitude 29°E-38°E). In order to meet the objectives
of this study, monthly average rainfall data from Tanzania Meteorological Agency
(TMA) and global marine environmental data, which consists gridded monthly sea
surface temperature (SST), sea level pressure (SLP) and zonal (U) and meridional (V)
wind components from National Oceanic and Atmospheric Administration (NOAA)
Earth System Research Laboratory were used. The rainfall data was used to develop
Standardized Precipitation Index (SPI) which was then used to find correlation with
global marine environmental parameters. Wavelet method was used to analyze
variations of power within the time series and dominant modes of rainfall variability
The study findings revealed that rainfall over the region is linked with SST over the
Indian Ocean, where warmer (cooler) western Indian Ocean is accompanied by high
(low) amount of rainfall over Tanzania. During wet (dry) years, weaker (stronger)
equatorial westerlies and anticyclone (cyclonic) anomaly over the southern tropics act
to reduce (enhance) the export of equatorial moisture away from East Africa. Not only
that, but also moisture influx from the northeast Indian monsoon has significant
influence on the rainfall over the region. During the wet years, strong northeasterly
Indian monsoon is evident over most of Tanzania while during the dry year the
northeasterly is seen to turn north hence denying moisture influx over Tanzania. In addition, increased (decreased) low level moisture influx from gulf of Guinea and
Congo basin tend to occur during the wet (dry) seasons, leading to enhanced (reduced)
low level moisture convergence over western part of Tanzania.
Results suggest the wettest season in record to be 1978/79 which can be classified as the
“Severely wet” and the driest season in record to be 1999/00 which can be classified as
“Moderate drought”. Different dominant periodicity modes have been observed over
the study period, but two of them seem to be more dominant over the whole study
period. These modes of rainfall have been identified at time scale of 2 and 7 years which
may be associated with the quasi biennial oscillation (QBO) and El Nino Southern
Oscillation (ENSO) respectively. Moreover, key areas over the Ocean have been
identified to be in between 5°S-18°S and 58°E-70°E for Indian Ocean and 2°N-17°S,
5°W-IO°E for Atlantic Ocean.
The study recommends a closer follow-up on the local variation of SST over these key
areas as they can help in forecasting year to year rainfall variability. Also responsible
institutions in the government should make use of the findings from this study as a
benchmark in improving agriculture sector and vigilance for extreme events.
Description
Dissertation
Keywords
Tanzania, Climate characteristics, Dominant periodicity mode