A comparison of Meteosat rainfall estimation techniques in Kenya

Two methods for estimating ten-day rainfall totals from Meteosat infra-red imagery were compared for the April-June 1996 ‘long rains’ of Kenya in an area covering the eastern highlands and the Tana and Athi river basins. One of these (the Bristol ‘B4’ method) was then used for rainfall estimation for the whole of Kenya, for November 1996 and the other, the TAMSAT ‘Cold Cloud Duration’ (CCD) method was used to estimate rainfall for the whole of Kenya for November 1997 to April 1998. April-June 1996 was an unusual season with very few large rainstorms. For this comparison period the B4 method gave better estimates of actual rainfall than the TAMSAT method because it used a variable cold cloud threshold temperature and ongoing calibration against rain gauge data. Comparison of ten-day CCD totals with rainfall for the 1997-1998 period indicated that using the TAMSAT method gave best rainfall estimates for the arid and semi-arid areas of eastern and northern Kenya and for months other than the main rainy season months of November and April. Both methods could be used successfully to identify periods with well below or well above average rainfall even over highland areas, and they are therefore useful for providing food security early warnings.