| dc.description.abstract | This study has investigated two of the most important aspects of rainfall over the North
eastern coast of Tanzania, namely onset and cessation dates (pentads) of the main long
rainy season. These aspects have considerable impacts on the rain-fed agriculture that is a
major contributor to the national economy and the well-being of the population farmers.
Farmers depend on the start or onset of the rains, which is highly variable, to plant crops
like maize for subsistence agriculture.
Thirty years (1978-2008) of daily rainfall data for north eastern coast of Tanzania were
analyzed with the aim to characterize the systems associated with the onset and cessation
of March to May rainfall of north eastern coast of Tanzania.
Several methodology were used in order to achieve the above objectives, including
Simple correlation and regression analysis, cumulative pentad totals which were used to
determine onset and cessation, graphical methods and other simple statistical methods.
Statistical packages used were Instat plus, SYSTAT 8.0 and Microsoft Excel
The cumulative pentad totals curves drawn in this study, shows that on averages the
onset start at pentad 15 and withdraw at pentad 31 in the Northern east coast of Tanzania.
And on average the March to May rainfall duration is of the length of 16 pentads (31-15)
The study demonstrated that there is large interannual variability of the onset, ranging
/ from pentad l3 to pentad 29 over the 30-yr period within the region, with a standard deviation
of 2.98.The withdrawal is less variable, ranging from pentad 29 to pentad 41
over the 30-year period within the region with standard deviation of 1.54.
The interannual variability of the onset and cessation time-series, as well as their fine
spatial representativity, has enabled the search for relationships with large-scale
atmospheric and oceanic fields on a seasonal time-scale like SST, ENSO, SOl, Low level
wind (850mb) and means sea level pressure.
It was found that early onset during study period was in pentad 13 (2002) and early
cessation in pentad 29 (2003) while late onset appeared in pentad 29 (1994) and late
cessation in pentad 41 (1999).and all these events were well explained by low level
wind(850mb) and mean sea level pressure pattern.
The study showed that the onset of the MAM season was due to ITCZ being in the region
and advection of onshore maritime air masses, while the cessation of the MAM were due
to the region of interest being under the influence of the Low level diluent and
curvature of the maritime air mass controlled by Heat low pressure system over Indian
subcontinent.
Lastly, the study showed that SST parameters, regional and global atmospheric
phenomena has indicates predicting potential over the region of interest. Hence one can
use them to come up with the forecast of the future conditions of the area | en |
