Floods in Africa
17 September 2007 00:00 UTC
The 2007 floods of Africa were reported by the UN as being one of the worst floodings in recorded history.
25 May 2022
17 September 2007
By Jochen Kerkmann and HansPeter Roesli (EUMETSAT)
The torrential rains started in July/August (see special Agrhymet bulletin (source: Agrhymet) and continued during the entire month of September. Over 20 countries have been affected in the continent, from Liberia in West Africa to Ethiopia and Kenya in East Africa.
In remote areas like the Sahel zone where conventional rain measurements are sparse, satellites provide essential data for measuring daily and monthly rain accumulations. An example for September 2007, calculated using microwave data from polar orbiting satellites and infrared data from geostationary satellites, is given in this UNOSAT report (source: UNOSAT).
In addition, satellites also allow one to monitor the effects of heavy rain on the ground, like increased vegetation cover and flood water on the ground. Two examples of this can be seen in the images below. Figure 1 is the Natural Colour RGB composite from Meteosat-9 showing areas covered by vegetation in green colour and water surfaces in black colour. In this image one can see the extension of the vegetation northwards into countries like Mali, Burkina Faso, Niger, Chad and Sudan. One can also see enlarged rivers like the Niger river in Mali and Nigeria or the Volta river in Ghana.
Figure 2 has been produced from night-time Meteosat-9 IR3.9 images by taking the maximum brightness temperature of all slots between 21:00 UTC and 01:00 UTC for the period 15–30 September 2007. This is a simple way of 'declouding' the images, ie finding cloud-free pixels during that period. In this image dark pixels represent either warm water surfaces, warm land (rock) surfaces, hot spots (fires) or urban heat islands. The white area in the lower right corner of the image is a persistently cloud-covered area where it was not possible to view the ground during the above mentioned period. One should note the well marked appearance of the rivers indicating high water level.
The use of night-time IR3.9 imagery for monitoring the extent of water surfaces (including floods) is not well known in the meteorological community. One example using the MSG IR3.9 channel is given in the case study of floods in Zambia and Sudan (December 2005).
Additional content
Met-9 IR3.9 enhanced night-time image (17 September, 22:00 UTC)
