Abstract
The spatio-temporal analysis of the performance of the March to May (MAM) 2020 rainfall and its societal implications to Northern Coastal Tanzania (NCT) including Zanzibar was investigated. The uniqueness of the October to December, 2019 (OND) rainfall and the extension of the January to February, 2020 rainfall in Zanzibar which coincided with MAM 2020 rainfall was among the issues which prolonged MAM 2020 rainfall in NCT and Zanzibar. The National Center for Environmental Prediction (NCEP) in collaboration with National Center for Atmospheric Research (NCAR). Reanalysis 1 datasets of u (zonal) and v (meridional) winds, sea surface temperatures anomalies, relative humidity, amount of precipitable water and ocean net flux were analyzed. Other datasets include the Tanzania Meteorological Authority (TMA) observed rainfall records, maximum and minimum temperatures. Moreover, TMA and Intergovernmental Climate Prediction and Analysis Center (ICPAC). MAM 2020 rainfall and temperature forecast reports were interpreted. Gridded and observed datasets were calculated into monthly and seasonal averages. As for observed data, long-term monthly and MAM percentage changes were calculated. Besides, the correlation between rainfall anomalies with an area-averaged SSTA for defined regions and stations in Zanzibar was performed. Lastly, the calculated monthly and seasonal rainfall was compared to MAM periods of 2016, 2017, 2018 and 2019. Results revealed that consecutive five MAM seasonal rainfall was among the highest ones in records with that of 2020 being exceptional. These MAM seasons had percentage contribution ranged from 68% - 212%, 150% - 304%, 22% - 163% and 57% - 170% for stations in Zanzibar and 130% - 230%, 57% - 168% and 230% - 706% for NCT station, respectively. Compared to previous MAM seasons of 2016-2019, MAM 2020 rainfall season was spatially well distributed in our study area with rainfall ranging from 1200 to 2100 mm and up to 900 in most Zanzibar and NCT stations. Indeed, the study revealed that the observed highest rainfall and flooding was enhanced by wet seasons of MAM 2019, OND 2019 and DFJ (2019-2020). Other dynamics which accelerated MAM 2020 rainfall were the higher SSTA ranged from 0.5°C - 1.5°C and 1.5°C - 2.5°C over Southwestern Indian Ocean (SWIO) and coastal Tanzania and the increased trend of area-averaged SSTA on various SWIO blocks. Besides, parameters including Rhum, PWR and wind regimes were supporting the MAM 2020 rainfall. The socio-economic implications of these rains were strong and spatially well distributed in Zanzibar. For instance, a death toll of about 10 people, a great number of road culverts were washed away, and about 3600 houses were fallen or damaged, leading to a significant number of homeless people. As for NCT, the catastrophes include loss of lives, increased water levels over Lake Victoria leading to flooded islands and re allocation of more than 1000 people. In Kenya, more than 116 people died and 40,000 people were displaced. Conclusively, the study has shown the uniqueness (i.e., strength and societal implications) of MAM 2020 compared to other seasons; hence more studies on understanding the factors affecting extreme rainfall seasons in East Africa are required.
Highlights
The northern coastal and hinterland zones of Tanzania including Zanzibar are among the East African (EA) countries that largely depend on rain-fed agriculture for the sustainability of its economy [1]
Similar results holds for the April, 2020 (Figure 2(b)) except that the Sea Surface Temperatures Anomalies (SSTA) strength over the EA coastal waters and Mozambican Channel was slightly reduced from 0.1 ̊C - 1.5 ̊C to 0 ̊C - 1 ̊C, and that of Somali coast was reduce from 1 ̊C - 2.5 ̊C to 0.5 ̊C - 1.5 ̊C except for very few small locations
As for May, 2020 the mapping of the SSTA presented In Figure 2(c) revealed that over the northern coastal Tanzania SSTA was further reduce to a range of −0.5 ̊C to 0 ̊C and that of East African Coastal Current (EACC) and Somali coast was reduced to range of 0.5 to 1.5 ̊C indicating the cessation of March to May (MAM) rainfalls, while that of the northeastern Madagascar at grid points defined by 2 ̊ - 10 ̊S and 45 ̊ - 60 ̊E was increased to range of 1.5 ̊C to 2.5 ̊C
Summary
The northern coastal and hinterland zones of Tanzania including Zanzibar are among the East African (EA) countries that largely depend on rain-fed agriculture for the sustainability of its economy [1]. Irrespective of employing about 70% (42% directly) (ZGS, 2007) of the labor force in Zanzibar, the planning and water resources management of this sector is faced by great challenges of climate variability and changes [2] [3] which results or posed major humanitarian concern and threats [3] as well as disrupting seasonal rainfall variability [4] Both the NCT and Zanzibar lie on two wet distinct climate regimes of long rains (Masika) which take place from March to May (MAM) and short rains (Vuli) which normally occur from October to December. The outcomes of these two forecasts as per the observation records from TMA (Zanzibar office) showed that the MAM 2019 rainfall season was among the wet ones with rainfall ranging from 1070.8 - 1223 mm (123% and 127% of the long term (1983-2019) mean for MAM in Unguja and Pemba (Zanzibar), respectively
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