Towards Improvement of Seasonal Rainfall Forecasting Through Model Output Statistics (MOS) Downscaling of Echam Forecasts over Tanzania

Journal of Kenya Meteorological Society


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Volume 2:2:2

Towards Improvement of Seasonal Rainfall Forecasting Through Model Output Statistics (MOS) Downscaling of Echam Forecasts over Tanzania

Ininda J.M.*, Athumani C.** and Mutemi J.N.*

*Department of Meteorology, University of Nairobi, **Tanzania Meteorological Agency, Dar es Salaam, Tanzania

Corresponding Author

Joseph M. Ininda

Department of Meteorology, University of Nairobi

P.O. Box 30197-00100 Nairobi- Kenya

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(Manuscript received 20 December 2007, in final form 03 October 2008)


Many economic activities such as agriculture and hydroelectric power generation are dependent on the availability of water. The main source of water in Tanzania is rainfall. The seasonal rainfall over Tanzania is highly variable both in time and space. Hence there is need for a forecasting model. The main objective of the study was towards improvement of seasonal rainfall forecasting through model output statistics (MOS) down scaling of the ECHAM forecast over Tanzania. ECHAM is a numerical weather prediction model developed at the European Centre for Medium Range Weather Forecasting, that has a comprehensive parameterization package developed at Hamburg, Germany. The data used in the study consists of monthly rainfall totals for 15 stations over Tanzania and wind and rainfall output from ECHAM for the period 1971-2004. The observed data were first subjected to quality control to ensure that they were homogenous and consistent. The ECHAM was forced with observed sea surface temperature. The analysis of the results indicated that the model was capable of simulating the observed climatological circulation and the annual rainfall pattern over Tanzanian. The skill of simulation was highest during the October to December (OND) rainfall season where the model explained as high as 74% of the variance at some locations while during March to May (MAM) the variance explained over most locations was less than 40%. This result was consistent with the previous studies that have shown high (low) correlation between the OND (MAM) rainfall and the SST. Moreover, the El Nino / Southern Oscillation (ENSO) signals are observed to be stronger during the OND season. The results from the study showed that the use of MOS for down scaling improves the simulation skill.

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