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Sahel, Soudan and Guinea Coast rainfall
The Sahel is the transitional semi-arid region of North Africa south of the Sahara desert between 12.5°N and 17.5°N. Its inhabitants are sensitive to rainfall amounts in the wet season (typically July to September), with droughts causing significant hardship. Rainfall is very variable from year to year and decade to decade. The Soudan is the belt immediately to the south of the Sahel between 12.5°N and 10°N. While the wet season is wetter on average than in the Sahel, it also has considerable variability. The Guinea Coast is a humid tropical region south of 10°N encompassing the countries of Cote d'Ivoire, Ghana, Togo, Benin and western Nigeria. Forecasts of the most likely of five rainfall categories (very wet, wet, average, dry or very dry) are produced using dynamical forecast models. Each of these categories has occurred in one-fifth of past years.
Important
- Long-range forecasts are unlike weather forecasts for the next few days
- Forecasts show the likelihood of a range of possible outcomes
- The most likely outcome in the forecast will not always happen
- Forecasts are for average conditions over a wide region and time period
- For more details on interpretation, see How to use our long-range predictions
Forecast
Issued May 2013
Our preliminary forecast for the July-August-September 2013 wet season indicates that the most likely category is 'wet' in the Sahel , 'wet' in the Soudan and 'average' in the Guinea Coast region. For a detailed look at the 2013 prediction, see the
preliminary forecast for July-August-September 2013
(PDF, 312 kB)
.
Verification
The
forecast for July-August-September 2012
(PDF, 473 kB)
favoured rainfall in the 'dry' category in the Sahel whilst the observed rainfall was in the 'very wet' category. The forecast for the Soudan indicated the 'dry' category as most likely whilst the observed rainfall was in the 'wet' category. The forecast for the Guinea Coast favoured the 'dry' category whilst the observed rainfall was in the 'dry' category. Therefore the forecast for the Guinea Coast region provided good guidance whilst the forecasts for the more northern regions were misleading.
The table below compares observed outcomes with our past forecasts. Overall, the correlations between the predicted and observed category are 0.10 for the Sahel, 0.13 for the Soudan, and 0.29 for the Guinea Coast.
In general, these do not represent a statistically significant level of skill. Our current forecast methods do demonstrate skill, however, being considerably better than earlier methods when tested in forecasts of past years.
| Year | Sahel | Soudan | Guinea Coast | |||
|---|---|---|---|---|---|---|
| Predicted | Observed | Predicted | Observed | Predicted | Observed | |
| 1992 | Dry | Dry | Very Dry | Average | Very Dry | Dry |
| 1993 | Very Dry or Dry | Dry | Very Dry | Very Dry | Dry or Average | Average |
| 1994 | Very Dry or Dry | Wet | Dry or Very Dry | Average | Dry or Average | Average |
| 1995 | Average | Average | Dry | Dry | Very Wet | Wet |
| 1996 | Dry or Average | Very Dry | Average | Very Dry | Very Wet | Average |
| 1997 | Dry or Average | Very Dry | Dry or Average | Very Dry | Dry | Very Dry |
| 1998 | Very Dry | Average | Very Dry | Average | Wet or Very Wet | Dry |
| 1999 | Wet | Very Wet | Wet | Wet | Very Wet | Wet |
| 2000 | Wet | Dry | Wet | Dry | Wet | Dry |
| 2001 | Wet | Dry | Wet | Dry | Average | Average |
| 2002 | Average | Average | Average | Dry | Average | Dry |
| 2003 | Very Wet | Wet | Wet | Wet | Very Dry | Average |
| 2004 | Very Wet | Average | Average | Dry | Very Dry | Dry |
| 2005 | Very Wet | Average | Average | Dry | Very Dry | Dry |
| 2006 | Average or Wet | Average | Dry or Average | Average | Dry or Average | Dry |
| 2007 | Dry or Average | Wet | Dry or Average | Average | Dry or Average | Wet |
| 2008 | Wet | Wet | Wet | Wet | Wet | Wet |
| 2009 | Dry or Average | Wet | Dry or Average | Average | Average or Wet | Dry |
| 2010 | Average | Wet | Dry | Wet | Dry or Very Dry | Very Wet |
| 2011 | Wet | Average | Dry | Average | Dry or Very Dry | Dry |
| 2012 | Dry | Very Wet | Dry | Wet | Dry | Dry |
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