The Mechanisms associated with September to November (SON) rainfall over Uganda during the recent decades
Abstract
This study revisits teleconnections associated with the anomalous events of September to November
(SON) rainfall over Uganda during 1981-2019, owing to the recent intensification of extreme events.
Empirical Orthogonal Function (EOF), Composite and Correlation analysis are employed to examine the variability of SON rainfall over the study domain and associated circulations anomalies. Thefirst EOF mode (dominant mode) displays a positive monopole pattern and explains 67.2% of the variance. The results revealed that SON rainfall is largely influenced by a Walker circulation mode over the
Indian Ocean, whereby, wet events are associated with an ascending limb of the Walker circulation on
the western part of the Indian Ocean characterized by convergence at low levels and divergence at upper level. The study showed that SON rainfall is positively (negatively) correlated with Indian ocean (Atlantic Ocean) sea surface temperatures (SST). Furthermore, Indian Ocean Dipole (IOD) events have
impact on SON rainfall with strong positive correlation, whereas Southern Oscillation Index (SOI) revealed negative correlation. The results also reveal that there is a lag in ENSO and IOD episodes during
wet/dry events over the region. ENSO and IOD also tend to extend the rainfall season of SON and thus
study of extreme events may not be well captured by studies focusing on SON. Future studies might
consider the season of October to December or December to February. These phenomena need to be
closely monitored and considered when making seasonal forecasts.
References
Ayugi, B. O., Tan, G., Ongoma, V., & Mafuru, K. B. (2018). Circulations associated with variations in boreal spring rainfall over Kenya. Earth Systems and Environment, 2(2), 421-434. https://doi.org/10.1007/s41748-018-0074-6
Ayugi, B., Tan, G., Ullah, W., Boiyo, R., & Ongoma, V. (2019). Inter-comparison of remotely sensed precipitation datasets over Kenya during 1998–2016. Atmospheric Research, 225, 96-109. https://doi.org/10.1016/j.atmosres.2019.03.032
Basalirwa, C. P. K. (1995). Delineation of Uganda into climatological rainfall zones using the method of principal component analysis. International Journal of climatology, 15(10), 1161-1177.. https://doi.org/10.1002/joc.3370151008
Bjornsson, S. & Venegas, H. (1997) A manual for EOF andSVD Analyses of Climatic Data. CGCRReport No. 97-1, McGill University, 8–27.
Black, E., Slingo, J., & 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(1), 74-94. doi:10.1175/1520493(2003)131<0074:AOSOTR>2.0.CO;2
Copernicus Climate Change Service (C3S). (2017). ERA5: Fifth generation of ECMWF atmospheric reanalyses of the global climate.Copernicus Climate change Service Climate Data Store (CDS).https://cds.climate.copernicus.edu/cdsapp#!/home. (Accessed 05.11.2020)
Dinku, T., Funk, C., Peterson, P., Maidment, R., Tadesse, T., Gadain, H., & Ceccato, P. (2018). Validation of the CHIRPS satellite rainfall estimates over eastern Africa. Quarterly Journal of the Royal Meteorological Society, 144, 292-312. DOI: 10.1002/qj.3244
Dommenget, D., & Latif, M. (2002). A cautionary note on the interpretation of EOFs. Journal of climate, 15(2), 216-225.
Egeru, A., Barasa, B., Nampijja, J., Siya, A., Makooma, M. T., & Majaliwa, M. G. J. (2019). Past, present and future climate trends under varied representative concentration pathways for a sub-humid region in Uganda. Climate, 7(3), 35.
Finney, D. L., Marsham, J. H., Rowell, D. P., Kendon, E. J., Tucker, S. O., Stratton, R. A., & Jackson, L. S. (2020). Effects of explicit convection on future projections of mesoscale circulations, rainfall, and rainfall extremes over Eastern Africa. Journal of Climate, 33(7), 2701-2718. DOI: 10.1175/JCLI-D-19-0328.1
Funk, C., Peterson, P., Landsfeld, M., Pedreros, D., Verdin, J., Shukla, S., Husak, G., Rowland, J., Harrison, L., Hoell, A. & Michaelsen, J. (2015). The climate hazards infrared precipitation with stations—a new environmental record for monitoring extremes. Scientific data, 2(1), 1-21. https://doi.org/10.1038/sdata.2015.66
Government of Uganda, GOU. (2015). Economic Assessment of the Impacts of Climate Change in Uganda. Final Study Report. Ministry of Water and Environment, Climate Change Department, Kampala. url: https://cdkn.org/wp-content/uploads/2015/12/Uganda_CC-economics_Final-Report2.pdf
Hastenrath, S., Polzin, D., & Camberlin, P. (2004). Exploring the predictability of the ‘short rains’ at the coast of East Africa. International Journal of Climatology: A Journal of the Royal Meteorological Society, 24(11), 1333-1343. doi:10.1002/joc.1070.
Hoell, A., Funk, C., & Barlow, M. (2014). La Niña diversity and northwest Indian Ocean rim teleconnections. Climate dynamics, 43(9-10), 2707-2724. doi:10.1007/s00382-014-2083-y.
Indeje, M., Semazzi, F. H., & Ogallo, L. J. (2000). ENSO signals in East African rainfall seasons. International Journal of Climatology: A Journal of the Royal Meteorological Society, 20(1), 19-46. https://doi.org/10.1002/(SICI)1097-0088(200001)20:1<19::AID-JOC449>3.0.CO;2-0
Liebmann, B., Hoerling, M. P., Funk, C., Bladé, I., Dole, R. M., Allured, D., Quan X., Pegion, P. & Eischeid, J. K. (2014). Understanding recent eastern Horn of Africa rainfall variability and change. Journal of Climate, 27(23), 8630-8645. doi:10.1175/JCLI-D-13-00714.1.
Limbu, P. T. S., & Guirong, T. (2019). Relationship between the October-December Rainfall in Tanzania and the Walker Circulation Cell over Indian Ocean. Meteorologische Zeitschrift, 28(6), 453-469.DOI 10.1127/metz/2019/0939.
Lorenz, E. N. (1956). Empirical orthogonal functions and statistical weather prediction. Technical report, StatisticalForecast Project Report 1. Department of Meteorology. MIT, 49pp.
Mafuru, K. B., & Guirong, T. (2020). The influence of ENSO on the upper warm temperature anomaly formation associated with the March–May heavy rainfall events in Tanzania. International Journal of Climatology, 40(5), 2745-2763. https://doi.org/10.1002/joc.6364
Makkonen, L. (2006). Plotting positions in extreme value analysis. Journal of Applied Meteorology and Climatology, 45(2), 334-340.
Manatsa, D., Chipindu, B., & Behera, S. K. (2012). Shifts in IOD and their impacts on association with East Africa rainfall. Theoretical and Applied Climatology, 110(1), 115-128. doi:10.1007/s00704-012-0610-5.
Manatsa, D., Morioka, Y., Behera, S. K., Matarira, C. H., & Yamagata, T. (2014). Impact of Mascarene High variability on the East African ‘short rains’. Climate dynamics, 42(5-6), 1259-1274. doi:10.1007/s00382-013-1848-z.
Manatsa, D., Mudavanhu, C., Mushore, T. D., & Mavhura, E. (2016). Linking major shifts in East Africa ‘short rains’ to the Southern Annular Mode. International Journal of Climatology, 36(4), 1590-1599. doi:10.1002/joc.4281
Mutai, C., Polzin, D., & Hastenrath, S. (2012). Diagnosing Kenya rainfall in boreal autumn: Further exploration. Journal of climate, 25(12), 4323-4329. doi:10.1175/JCLI-D-11-00414.1.
Ngarukiyimana, J. P., Fu, Y., Yang, Y., Ogwang, B. A., Ongoma, V., & Ntwali, D. (2018). Dominant atmospheric circulation patterns associated with abnormal rainfall events over Rwanda, East Africa. International Journal of Climatology, 38(1), 187-202. doi: 10.1002/joc.5169
Ngoma, H., Wen, W., Ojara, M., & Ayugi, B. (2021). Assessing current and future spatiotemporal precipitation variability and trends over Uganda, East Africa, based on CHIRPS and regional climate model datasets. Meteorology and Atmospheric Physics, 1-21.
Nicholson, S. E., & Kim, J. (1997). The relationship of the El Niño–Southern oscillation to African rainfall. International Journal of Climatology: A Journal of the Royal Meteorological Society, 17(2), 117-135. doi:10.1002/(SICI)1097-0088(199702)17:2<117: AID-JOC84>3.0.CO;2-O
Nicholson, S. E. (1996). A review of climate dynamics and climate variability in eastern Africa. In Johnson T.C. & Odada E.O. (Eds.) The Limnology, Climatology, and Paleoclimatology of the East African Lakes, (pp. 25–56), Amsterdam: Gordon and Breach Publ.
Nicholson, S. E.,Leposo, D&Grist, J.P., (2001). The relationship between El Niño and drought over Botswana, Journal of Climate., 14(3), 323–335,doi:10.1175/1520-0442(2001)014<0323:TRBENO>2.0.CO;2.
Nicholson, S. E. (2015). Long‐term variability of the East African ‘short rains’ and its links to large‐scale factors. International Journal of Climatology, 35(13), 3979-3990. doi:10.1002/joc.4259.
Nicholson, S. E. (2017). Climate and climatic variability of rainfall over eastern Africa. Reviews of Geophysics, 55(3), 590-635. doi:10.1002/2016RG000544
Nicholson, S. E. (2018). The ITCZ and the seasonal cycle over equatorial Africa. Bulletin of the American Meteorological Society, 99(2), 337-348. https://doi.org/10.1175/BAMS-D-16-0287.1
Nsubuga, F. W., & Rautenbach, H. (2018). Climate change and variability: a review of what is known and ought to be known for Uganda. International Journal of Climate Change Strategies and Management. Doi 10.1108/IJCCSM-04-2017-0090
Nsubuga, F.N.W., Olwoch, J. M., Rautenbach, C. D., & Botai, O. J. (2014). Analysis of mid-twentieth century rainfall trends and variability over southwestern Uganda. Theoretical and applied climatology, 115(1), 53-71. https://doi.org/10.1007/s00704-013-0864-6
Ogwang, B., Nimusiima, A., Tindamanyire, T., Serwanga, M., Ayesiga, G., Ojara, M., Ssebabi, F., Gugwa, G., Nsubuga, Y., Atim, R., & Aribo, L. (2016). Characteristics and changes in SON rainfall over Uganda (1901-2013). Journal of Environmental and Agricultural Sciences, 8, 45-53.
Ogwang, B. A., Ongoma, V., Xing, L., & Ogou, K. F. (2015). Influence of Mascarene high and Indian Ocean dipole on East African extreme weather events. Geographica Pannonica, 19(2), 64-72. https://doi.org/10.5937/geopan1502064o
Ogwang, B. A., Chen, H., Li, X., & Gao, C. (2014). The influence of topography on East African October to December climate: sensitivity experiments with RegCM4. Advances in Meteorology. https://doi.org/10.1155/2014/143917
Ogwang, B. A., Guirong, T., & Haishan, C. (2012). Diagnosis of September-November drought and the associated circulation anomalies over Uganda. Pakistan Journal of Meteorology, 9(2).11-24
Ojara, M. A., Lou, Y., Aribo, L., Namumbya, S., & Uddin, M. J. (2020). Dry spells and probability of rainfall occurrence for Lake Kyoga Basin in Uganda, East Africa. Natural Hazards, 100(2), 493-514.. https://doi.org/10.1007/s11069-019-03822-x
Ongoma, V., Tan, G., Ogwang, B., & Ngarukiyimana, J. (2015). Diagnosis of seasonal rainfall variability over East Africa: a case study of 2010-2011 drought over Kenya. Pakistan Journal of Meteorology, 11(22), 13-21.
Phillips, J., & McIntyre, B. (2000). ENSO and interannual rainfall variability in Uganda: implications for agricultural management. International Journal of Climatology: A Journal of the Royal Meteorological Society, 20(2), 171-182.
Reliefweb., (2020). UgandaKey Message Update:Areas affected by flooding and landslides face deteriorating food security as food prices rise, January 2020. Available at: https://reliefweb.int/report/uganda/uganda-key-message-update-areas-affected-flooding-and-landslides-face-deteriorating. (Accessed 18.12.2020).
Saji, N. H., Goswami, B. N., Vinayachandran, P. N., & Yamagata, T. (1999). A dipole mode in the tropical Indian Ocean. Nature, 401(6751), 360-363. https://doi.org/10.1038/43854
Sylla, M. B., Giorgi, F., Coppola, E., & Mariotti, L. (2013). Uncertainties in daily rainfall over Africa: assessment of gridded observation products and evaluation of a regional climate model simulation. International Journal of Climatology, 33(7), 1805-1817. https://doi.org/10.1002/joc.3551
Uganda National Meteorological Authority (UNMA). (2019). September to December 2019 seasonal rainfall outlook over Uganda. Available at: http://www.unma.go.ug
Wainwright, C. M., Finney, D. L., Kilavi, M., Black, E., & Marsham, J. H. (2021). Extreme rainfall in East Africa, October 2019–January 2020 and context under future climate change. Weather, 76(1), 26-31. doi: 10.1002/wea.3824
Williams, A. P., & Funk, C. (2011). A westward extension of the warm pool leads to a westward extension of the Walker circulation, drying eastern Africa. Climate Dynamics, 37(11-12), 2417-2435. https://doi.org/10.1007/s00382-010-0984-y
