Gauge data from a West African network of 920 stations are used to assess Tropical Rainfall Measuring Mission (TRMM) satellite and blended rainfall products for 1998. In this study, mean fields, scattergrams, and latitudinal transects for the months of May-September and for the 5-month season are presented. Error statistics are also calculated. This study demonstrates that both the TRMM-adjusted Geostationary Observational Environmental Satellite precipitation index (AGPI) and TRMM-merged rainfall products show excellent agreement with gauge data over West Africa on monthly-to-seasonal timescales and 2.5Њ ϫ 2.5Њ latitude/longitude space scales. The root-mean-square error of both is on the order of 0.6 mm day Ϫ1 at seasonal resolution and 1 mm day Ϫ1 at monthly resolution. The bias of the AGPI is only 0.2 mm day Ϫ1 , whereas the TRMM-merged product shows no bias over West Africa. Performance at 1.0Њ ϫ 1.0Њ latitude/longitude resolution is also excellent at the seasonal scale and good for the monthly scale. A comparison with standard rainfall products that predate TRMM shows that AGPI and the TRMM-merged product perform as well as, or better than, those products. The AGPI shows marked improvement when compared with the GPI, in reducing the bias and in the scatter of the estimates. The TRMM satellite-only products from the precipitation radar and the TRMM Microwave Imager do not perform well over West Africa. Both tend to overestimate gauge measurements.
Since 1970 the West African Sahel has experienced a significant drought which, according to some authors, corresponds to a discontinuity (abrupt change) in the rainfall series. An annual rainfall index was calculated over the period from 1896 to 2000, with a selection of 21 synoptic stations updated regularly by the Agrhymet Regional Centre in Niamey. Several statistical analyses of the index confirmed the previous descriptions, particularly the significance of the drought since 1970 and a nonstationarity, with abrupt change in the series between 1969 and 1970. Although the two recent wet years, 1994 and 1999, gave some hope of an end to the drought, the statistical results and the temporal distribution of the dry and wet years showed that the drought was not over at the end of 2000.
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REPLY to "The Sahelian drought may have ended during the 1990s"The 1990s rainfall in the Sahel: the third driest decade since the beginning of the century
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