An Assessment of the Seasonal Rainfall and Its Societal Implications in Zanzibar Islands during the Season of October to December, 2019

Abstract

The assessment of the performance of the October to December (OND), 2019 rainfall season in Zanzibar (Unguja and Pemba) with reference to local downscaled Tanzania Meteorological Authority (TMA) forecast, and regional (Intergovernmental Authority on Development Climate Prediction and Application Center (IGAD-ICPAC) weather forecasts were assessed by comparing the long term average of OND rainfall data and previous OND rainfall seasons of 2016, 2017 and 2018 as well as extreme positive Indian Ocean Dipole (IOD) during OND seasons of 1961, 1994, 1997, 2006 and 2019 for Zanzibar. The study assessed zonal (u) and meridional (v) winds at 850 and 200 mb, monthly and dekadal sea surface temperature (SST); the Madden Julien Oscillations (MJO) forecast reports and the ocean heat content data. Both gridded and observed datasets were processed into dekadal, monthly and seasonal averages and then analysed. The results revealed that, based on the observations, above normal rainfall of 936 and 908 mm were reported at stations of Kisauni (Unguja) and Karume airport (Pemba) during 2019 OND season. This amount was the first and second ever recorded for the extreme positive IOD during OND seasons of

Assessment of the Off-season Rainfall of January to February 2020 and Its Socio Economic Implications in Tanzania: A Case Study of the Northern Coast of Tanzania

“…Moreover, the south-north oscillation of the ITCZ in combination with atmospheric circulation features (Hadley cell) control the rainfall regime in East Africa [5][6][7][8] . It is well-known that the agricultural activities over Zanzibar and NCT are rain fed [9,10] and about 85% of most of the economic activities depends on the climate-driven agricultural sector [11] . The seasonal shifting of rainfall (i.e.…”

“…the early onset of the forecasted rainfall (e.g. MAM, 2020; OND, 2020 [10] in Tanzania) results in either enhanced or decline precipitation, which in turn affects the socio economical set up of the society. For instance, [12] has reported an increase in annual timescale of mean temperature anomaly, percentage of warm days, percentage of warm nights, and a decrease in percentage of cold days and nights by 0.69˚C, 9.37%, 12.05%, 7.64% and 10.00%, in most regions of Tanzania including Dares-Salaam, Zanzibar, Mtwara, Kilimanjaro and Mbeya, respectively.…”

“…Climatologically, NCT lies between two distinct rainfall regimes (bimodal) of long rains which takes place on March to May (MAM) and short rains from October to December (OND) [7,13,14,15,10] . The rainfall regime in Tanzania was previously assessed by previous studies using long term rainfall data of high resolution regional climate models and historical observations to analyse the rainfall cycles, however, the seasonal patterns still seem to have maintained the same pattern [14,10] . In NCT region most cases of short rain seasons are dominated by poor temporal and spatial coverage except few years e.g.…”

“…In NCT region most cases of short rain seasons are dominated by poor temporal and spatial coverage except few years e.g. OND 2019 [12,10] . Also the onset and cessations of short rains in East African (EA) and NCT in particular is very poor with low predictability especially on exceptionally dry years [16] .…”

“…Other dynamic which may influence the JF off-season rainfall over this region are the existence of tropical cyclones which increases its frequency during December to March [15,19] . Moreover, [15,20] and [10] have noted that TCs either enhances or declines the rainfall in coastal region including the NCT, while [21] had shown that westerly flows from Congo air mass enhances the rainfall when it coincides with Phase 3 and 4 of the MJO, and during TCs. Indeed, [22] has noted that during December to March, the northeast monsoon brings dry continental air into East Africa, which declined rainfall during these months.…”