Diagnosis of September - November Drought and the Associated Circulation Anomalies Over Uganda

Ogwang B A, T Guirong, C Haishan

Abstract


Extreme weather and climate events such as floods and droughts are common in Uganda. These events have always had devastating impacts on various sectors of the country’s economy. In this study we investigate the drought events of September-November (SON) season and the associated circulation anomalies over Uganda for the period 1962-2007. A regional drought index (Z-index) with a scheme of grading severity of drought and flood is used to classify the drought/flood events using station rainfall data. The index successfully classified the drought and flood events, with SON heavy floods (droughts) experienced in the years 1967,1972,1977,1999, 2000 and 2001 (1974 1976,1979,1984,1985 and 1993). Analysis of the drought and flood years with respect to the different variables including wind, velocity potential and divergence/convergence vectors revealed that the drought (flood)
years were characterized by divergence (convergence) in the lower troposphere and convergence (divergence) at the upper level, implying sinking (rising) motion, especially over the western Indian Ocean and the study area. The anomaly convergence zone was identified within (outside) the region of study during flood (drought) years.


Full Text:

Untitled

References


Bordi, I., S.Frigio, P.Parenti, A.Speranza and A.Sutera, 2001: The analysis of the Standardized Precipitation Index in the Mediterranean area: Regional patterns. Annali Di Geofisica, 44, N. 5/6, 979-993.

Cheng, X., G. Nitsche, J. M. Wallace, 1995: Robustness of Low-Frequency Circulation Patterns Derived from EOF and Rotated EOF Analyses. Journal of Climate, 8, 1709-1713.

Dai, A., K. E. Trenberth, and T. Qian, 2004: A Global Dataset of Palmer Drought Severity Index for 1870–2002: Relationship with Soil Moisture and Effects of Surface Warming. Journal of Hydrometeorology, 5, 1117-1130.

Dambul, R., 2005: The Relationships between Large-scale Atmospheric circulation and Surface Climate. PhD Thesis, University of East Anglia, England

Folland, C. K., 1983: Regional-Scale Interannual variability of climate. A north-west European perspective. Meteorological Magazine, 12: 163 -187.

Gruntfest, E.and J. Handmer, 2001: Copying with flash floods, Volume 77, NATO science series: Environmental security.

Indeje, M., F.H.M. Semazzi and L. J. Ogallo, 2000: ENSO signals in East African rainfall and their prediction potentials. International Journal of climatology, 2000, 20: 19 – 46.

Ininda, J.M., 1995: Numerical simulation of the influence of sea surface temperature anomalies on the East African seasonal rainfall. PhD. Thesis, Department of Meteorology, University of Nairobi, Kenya.

Jonawiak, J.E., 1988: An investigation of Interannual Rainfall Variability in Africa. Journal of climatology, 1: 240 - 255.

Kabanda, T. A., M.R. Jury, 1999: Inter-annual variability of short rains over northern Tanzania. Climate Research, 13: 231 - 241.

Mutemi, J.N., 2003: Climate anomalies over eastern Africa associated with various ENSO evolution phases. Ph.D. Thesis, University of Nairobi, Kenya.

Nicholson, S.E. 1996: A review of Climate Dynamics and Climate Variability in Eastern Africa: Department of Meteorology, Florida State University, Tallahassee, Florida, United States, 25 -56.

Ogallo, L. J., 1988: Relationships between seasonal rainfall in East Africa and the southern oscillation Journal of Climatology, 8, 31 – 43

Okoola, R.E, 1996: Space-Time characteristics of the ITCZ over Equatorial East Africa during anomalous rainfall years. Ph.D. Thesis, University of Nairobi.

Okoola, R.E., 1998: Mid-tropospheric Circulation patterns associated with extreme dry and wet episodes over equatorial eastern Africa during the Northern Hemisphere spring. Journal of Climatology, 1161 -1169.

Okoola, R.E., 1999: A diagnostic study of the East African monsoon circulation during the northern hemisphere spring season. International Journal of Climatology, 19, 143-169.

Barry, R. G. and R. J. Chorley, 2003: Atmosphere, weather and climate. Eighth edition, 462 pp. Ropelewski C.F and M.S Halpert, 1987: Global and regional scale precipitation patterns associated with the ElNiño/Southern Oscillation. Mon Weather Rev, 115, 1602-1626.

Tan, G, S. Zhaobo, H. Chen, 2003: Diagnosis of summer time floods/droughts and their atmospheric circulation anomalies over north China. ACTA Meteorological Sinica, 17: 257 - 273

Walsh, J. E. and A. Mostek, 1980: A Quantiative Analysis of Meteorological Anomaly patterns over the United States, 1900 – 977.Mon Weather Rev, 108, 615-630.

Wilks, S.D, 2006: Statistical Methods in the Atmospheric Sciences. Second edition, Volume 91, International geophysics series.


Refbacks

  • There are currently no refbacks.