Heavy rainfall is one of the primary causes of flood during rainy season in Tanzania leading to severe socio-economic impacts. The study aimed at assessing and characterizing the variability of Heavy Rainfall Events (HREs) using Empirical Orthogonal Function (EOF), Mann-Kendal (MK) trend test, Correlation and Composite analysis methods. Based on the daily-observed precipitation and reanalysis data sets for the October to December (OND) rainfall season of 35 years (1981-2015), the spatial and temporal characteristics of HREs in Tanzania are studied. The relationship between heavy rainfall (HR) and large-scale circulation anomalies including the Indian Ocean dipole (IOD) and El Ni ? o southern oscillation (ENSO) indices was assessed. The study found that, approximately 590 HREs were concentrated over northern sector and coastal belt of Tanzania. The monthly variability indicates that HREs are more pronounced in December followed by November while October being the least affected. The occurrence of HREs over the Lake Victoria, Kigoma and Tabora is largely attributed to low-level convergence of westerlies and enhanced moisture from Congo basin accompanied by a pronounced rising limb of Indian Walker circulation cell. A time-series analysis of HRE exhibits an inter-annual variation characterized by a slightly increasing trend, though the computed trends were not statistically significant at 95% confidence level. In most part of Tanzania HREs were positively correlated with both ENSO and IOD indices, underscoring the critical role of ENSO and Indian Ocean dynamic in modulating rainfall variability over the region. In general, it has been found that most of the HREs are generally triggered or amplified by large-scale circulation patterns such as ENSO and IOD.
IPCC (2018) IPCC Special Report on the Impacts of Global Warming of 1.5 °C.
Lal, P.N., et al. (2012) National Systems for Managing the Risks from Climate Extremes and Disasters.
Verdin, J., Funk, C., Senay, G. and Choularton, R. (2005) Climate Science and Famine Early Warning. Philosophical Transactions of the Royal Society B Biological Sciences, 360, 2155-2168. https://doi.org/10.1098/rstb.2005.1754
Epstein, P.R. (1999) Climate and Health. Science, 285, 347-348. https://doi.org/10.1126/science.285.5426.347
Funk, C., et al. (2005) Recent Drought Tendencies in Ethiopia and Equatorial Subtropical Eastern Africa.
Reason, C.J. and Jagadheesha, D. (2005) A Model Investigation of Recent ENSO Impacts over Southern Africa. Meteorology and Atmospheric Physics, 89, 181-205. https://doi.org/10.1007/s00703-005-0128-9
Hastenrath, S., Polzin, D. and Mutai, C. (2006) Diagnosing the 2005 Drought in Equatorial East Africa. Journal of Climate, 20, 4628-4637. https://doi.org/10.1175/JCLI4238.1
Behera, S.K., et al. (2006) Erratum: Paramount Impact of the Indian Ocean Dipole on the East African Short Rains: A CGCM Study (Journal of Climate Vol. 18 (21) (4514-4530)). Journal of Climate, 19, 1361. https://doi.org/10.1175/JCLI3541.1
Birkett, C., Murtugudde, R. and Allan, T. (1999) Indian Ocean Climate Event Brings Floods to East Africa’s Lakes and the Sudd Marsh. Geophysical Research Letters, 26, 1031-1034. https://doi.org/10.1029/1999GL900165
Nyenzi, B.S. (1992) Analysis of Inter-Annual Variability of Rainfall over East Africa. Journal of the African Meteorological Society, 1, 57-79.
Kijazi, A.L. and Reason, C.J.C. (2009) Analysis of the 2006 Floods over Northern Tanzania. International Journal of Climatology, 29, 955-970. https://doi.org/10.1002/joc.1846
Hastenrath, S., Polzin, D. and Mutai, C. (2010) Diagnosing the Droughts and Floods in Equatorial East Africa during Boreal Autumn 2005-08. Journal of Climate, 23, 813-817. https://doi.org/10.1175/2009JCLI3094.1
Kabanda, T.A. and Jury, M.R. (1999) Inter-Annual Variability of Short Rains over Northern Tanzania. Climate Research, 13, 231-241. https://doi.org/10.3354/cr013231
Indeje, M., Semazzi, F.H.M. and Ogallo, L.J. (2000) ENSO Signals in East African Rainfall Seasons. International Journal of Climatology, 20, 19-46. https://doi.org/10.1002/(SICI)1097-0088(200001)20:1 3.0.CO;2-0
Ummenhofer, C.C., Sen Gupta, A., England, M.H. and Reason, C.J.C. (2009) Contributions of Indian Ocean Sea Surface Temperatures to Enhanced East African Rainfall. Journal of Climate, 22, 993-1013. https://doi.org/10.1175/2008JCLI2493.1
Brigadier, L., Ogwang, B.A., Ongoma, V., Ngonga, C. and Nyasa, L. (2016) Diagnosis of the 2010 DJF Flood over Zambia. Natural Hazards, 81, 189-201. https://doi.org/10.1007/s11069-015-2069-z
Kalnay, E., et al. (1996) The NCEP/NCAR 40-Year Reanalysis Project. Bulletin of the American Meteorological Society, 77, 437-471. https://doi.org/10.1175/1520-0477(1996)077 2.0.CO;2
Smith, T.M., Reynolds, R.W., Peterson, T.C. and Lawrimore, J. (2008) Improvements to NOAA’s Historical Merged Land-Ocean Surface Temperature Analysis (1880-2006). Journal of Climate, 21, 2283-2296. https://doi.org/10.1175/2007JCLI2100.1
Saji, N.H., Goswani, B.N., Vinayachandran, P.N. and Yamagata, T. (1999) A Dipole Mode in the Tropical Indian Ocean. Nature, 401, 360-363. https://doi.org/10.1038/43854
Muhati, F., Ininda, J. and Opijah, F.J. (2007) Relationship between ENSO Parameters and the Trends and Periodic Flactuations in East African Rainfall. Journal of Kenya Meteorological Society, 1, 20-43.
Nasri, M. and Modarres, R. (2009) Dry Spell Trend Analysis of Isfahan Province, Iran. International Journal of Climatology, 29, 1430-1438. https://doi.org/10.1002/joc.1805
Limbu, P.T.S. and Guirong, T. (2019) Relationship between the October-December Rainfall in Tanzania and the Walker Circulation Cell over Indian Ocean. Meteorologische Zeitschrift, 28, 453-469. https://doi.org/10.1127/metz/2019/0939
Mosmann, J., Castro, V., Fraile, A., Dessens, R. and Sánchez, J. (2004) Detection of Statistically Significant Trends in the Summer Precipitation of Mainland Spain. Atmospheric Research, 70, 43-53. https://doi.org/10.1016/j.atmosres.2003.11.002
Hotelling, H. (1933) Analysis of a Complex of Statistical Variables into Principal Components. Journal of Educational Psychology, 24, 498-520. https://doi.org/10.1037/h0070888
Bjornsson, H. and Venegas, S.A. (1997) A Manual for EOF and SVD Analyses of Climate Data.
Mafuru, K.B. and Guirong, T. (2018) Assessing Prone Areas to Heavy Rainfall and the Impaction of the Upper Warm Temperature Anomaly during March-May Rainfall Season in Tanzania. Advances in Meteorology, 2018, Article ID: 8353296. https://doi.org/10.1155/2018/8353296
Yount, R. (2006) Correlation Coefficients. Research Design and Statistical Analysis in Christian Ministry. 4th Edition. Department of Foundations of Education, School of Religious Education, Southwestern Theological Seminary, Fort Worth, TX, 71-72.
Black, E., Slingo, J. and Sperber, K.R. (2003) An Observational Study of the Relationship between Excessively Strong Short Rains in Coastal East Africa and Indian Ocean SST. Monthly Weather Review, 131, 74-94. https://doi.org/10.1175/1520-0493(2003)131 2.0.CO;2
Clark, C.O., Webster, P.J. and Cole, J.E. (2003) Interdecadal Variability of the Relationship between the Indian Ocean Zonal Mode and East African Coastal Rainfall Anomalies. Journal of Climate, 16, 548-554. https://doi.org/10.1175/1520-0442(2003)016 2.0.CO;2
Nicholson, S.E. (1996) A Review of Climate Dynamics and Climate Variability in Eastern Africa. In: Johnson, T. and Odada, E., Eds., The Limnology, Climatology and Paleoclimatology of the East African Lakes, CRC Press, Boca Raton, 25-56. https://doi.org/10.1201/9780203748978-2
Mbululo, Y. and Nyihirani, F. (2012) Climate Characteristics over Southern Highlands Tanzania. Atmospheric and Climate Sciences, 2, 454-463. https://doi.org/10.4236/acs.2012.24039