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Actueel weer
Zondag 30 september
33°
Zonnig
Weersvoorspelling
Do 1 okt 33°regenachtig
Za 2 okt 33°regenachtig
Zo 3 okt 33°regenachtig
Actuele waterstand
Zondag 30 september
657cm
Hoog
WeersvoorspellingPeak flow level (cm)
Minimum 660
Mean 663
Maximum 666
Table of contents
Recent rainfall in West Africa
Back to Weather and Climate

Recent rainfall in West Africa

Rainfall is measured on a daily basis in many, but declining number of weather stations across West Africa. Satellites are increasingly used to estimate and forecast rainfall, also in West Africa. These data are used to present recent information on rainfall.

General pattern

The river flow of the Niger and Bani Rivers depends on the amount of rainfall in the Upper Niger Basin. Variation in the seasonal and annual precipitation in the basin directly translates in a variation in river flow, and ultimately determines the extent of the seasonal flooding of the Inner Niger Delta. The rainfall in the Upper Niger Basin is therefore a good indicator of the available water resources, not only for the river flow but also to estimate the conditions for agriculture. The rainfall in the Upper Basin in July-August is used by OPIDIN as an indicator of the flooding of the Inner Niger Delta 3-4 months later.

Rainfall is measured on a daily basis in many, but declining number of, weather stations across West Africa. Some of these data are made available through the World Meteorological Organisation (WMO). Today, also satellites are used to estimate and forecast rainfall across the world. The Famine Early Warning System website (FEWS) gives satellite-derived rainfall estimates for Africa. This information is used here to present information on recent rainfall.

Rainfall in the Upper Niger Basin

Using satellite-derived rainfall data, we calculated the accumulated amount of rainfall in the Upper Niger Basin during the current wet season (April – November) and compared this to rainfall in the past. The graph below shows whether the rainfall in the current season so far (yellow line) is relatively high or low. Note that satellite derived rainfall estimates may overestimate rainfall in some cases (see comparison in Long term rainfall data).



The accumulated amount of rainfall (km<sup>3</sup>) in the Upper Niger Basin during the current wet season (April – November) compared to the last 16 years (maximum, median and minimum calculated over 2001-2016). Graph based on daily satellite-derived rainfall; source: NOAA/FEWS.


The flow of the Bani and Niger River, and thus also the flooding of the Inner Niger Delta, is determined by the rainfall in the Upper Niger Basin upstream of the Inner Niger Delta, thus in the eastern part of Guinea-Conakry and the SW part of Mali. The daily estimated rainfall within this area represents the water resource in the basin.

The basic information on daily rainfall is derived from satellite images and made available through various websites. To aggregate these data in an accessible way, the daily rainfall in the Upper Niger Basin is converted to km3 water. The graph above shows this information from 1 April onwards in comparison to the rainfall over the same seven months during previous years (2001-2016). The accumulated amount of rainfall is a good indicator of the humidity of the season, where it comes to average rainfall in the basin. This indicator has been developed for OPIDIN to improve the prediction of the flood level in the Inner Niger Delta.

Recent rainfall

Daily rainfall is monitored by satellites and this gives the opportunity to make rainfall estimates (RFE) per region. Rainfall estimates with satellites are available from 2001 onwards, which makes it possible to compare the actual rainfall with the rainfall in the past. These data are presented in the graph below.



 

Next to the RFE data per region it is also possible to map the RFE.

The maps given below are taken from the Climate Prediction Centre from the US National Weather Service, showing the rainfall in West Africa during four recent days:

 

a) most recent daily estimate - total rainfall in mm

b) daily estimate, 1 day before a)

c) daily estimate, 2 days before a)


d) daily estimate, 3 days before a)

     Satellite-derived rainfall estimates; source NOAA/FEWS


The total estimated rainfall is also given for last week:

Last week - total rainfall in mm

Satellite-derived rainfall estimates (ARC2); source NOAA/FEWS


All maps above give rainfall estimates in mm, but to know whether the rainfall was above or below the long term-average, the results are presented in another way. Therefore recent rainfall is presented as a deviation from the long term-mean from the years before. This can be expressed by an absolute difference (deviation from the mean) in millimetres of estimated rainfall or by a relative difference showing the percentage of deviation from the long term-mean. Both types of information are displayed in the two maps underneath:

Absolute difference to long term-mean in mm

Relative difference to long term-mean as % deviation

Satellite-derived rainfall estimates (ARC2); source NOAA/FEWS

 

Rain forecast

Using the weather satellites, it is also possible to give a global prediction regarding the rainfall in the coming weeks. In the maps below, this prediction is given by FEWS for the coming week, and the week after the coming week. More detailed information about the weather forecasts can be found on the Climate Prediction Center from the US National Weather Service.

Rainfall forecast - next week

Rainfall forecast - week after next week

Rainfall forecast for the next week Rainfall forecast for the week after next week
Satellite-derived rainfall estimates (ARC2); source NOAA/FEWS

 

Rainfall in the current season so far

The flow of the rivers and the flooding of the Inner Niger Delta is not determined by the rainfall of the last week(s), but by the accumulated, total rainfall in the wet season. Also this information is gathered, based on the daily estimates of rainfall. The map below shows the total rainfall (mm) for the last 180 days in three ways: 

Rainfall during the last 180 days: total amount (mm)

 

Rainfall during the last 180 days: absolute deviation (in mm above or below the long-term average).

 

Rainfall during the last 180 days: relative deviation (in per cent above or below the long-term average)