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CASE STUDY 2 : Failure of short rainy season 2005


In a normal year, rains in East Africa fall from March to May during the long rainy season, and from October to December during the short rainy season. The rains recharge lakes and reservoirs and nurture plants from crops and pasture lands to natural vegetation. For East Africa, 2005 was anything but a normal year. The long rainy season produced little rain, and the short rainy season failed altogether. The failure of the short-season rains caused severe drought in large parts of Kenya in late 2005 and early 2006.

Comparison of the ’vegetation health and density’ for December 2003, 2004 and 2005 (images below) reveals that the vegetation health & density during the failed short rainy season of 2005 is lower compared to the previous years.

 
Vegetation health & density: December 2003 (left image), December 2004 (middle image), December 2003 (right image)


When looking at the vegetation health & density of the end of December compared with the average situation in the same period we clearly see that in large parts of Kenya vegetation is affected by the drought.

 
Vegetation health & density compared to average situation for the end of December 2003


In the graphs below the evolution of the ’vegetation health and density’ is plotted against the average situation for all land cover types in the Marsabit district for 2003 and 2005. In 2003 the vegetation conditions during the long rains were above average and vegetation conditions during the short rains (start in November) were comparable to the average situation. In 2005, however, vegetation health & density is slightly lower than average for the long rainy season and much lower than average for the short rainy season. Plotting the graph for herbaceous vegetation and closed woody vegetation, shows that herbaceous vegetation is much more affected by drought compared to the closed woody vegetation. The increase of the ‘vegetation health and density’ of 2005 takes place half April in stead of half March, which corresponds to a delay of the start of the growing season


Vegetation health & density in Marsabit district for 2003 and for average year


Vegetation health & density in Marsabit district for 2005 and for average year


Vegetation health & density for herbaceous land cover type in Marsabit district for 2005 and for average year


Vegetation health & density for closed woody land cover type in Marsabit district for 2005 and for average year


In the image showing vegetation health & density at the end of December 2005 for Marsabit district, the forested areas (Mount Marsabit, Mount Kulal, and Mount Nyioro) can easily be distinguished from the surrounding regions as they have a higher vegetation density (‘good’ and ‘very good’). From the image in which vegetation health & density is compared to the average situation at the end of December, it can be seen that these forests are not affected by the droughts. Only the edges of the forest are affected to some extent (especially for Mount Kulal). This illustrates the importance of forests as buffers against droughts.

   
 
Vegetation health & density at the end of December for Marsabit district: actual (left image) – compared to average situation (right image)


Other impacts of droughts can be observed on high spatial resolution data. By comparing the SWIR colour composite Landsat ETM+ image of 2005 with the one of 2000, we can observe that in 2005 the water in the most southern situated lake on Marsabit Mountain is completely depleted. Water has low reflectivity in both near infrared and shortwave infrared and therefore appears black or dark blue in SWIR colour composite images.


Landsat ETM+ SWIR colour composite image of Marsabit mountain: 2000 (left image)- 2005 (right image)


The amount of rain has a major impact on the crop production. The ‘vegetation growth rate’, which is an indication of the vegetation productivity, is also much lower in 2005 compared to 2003 and 2004. The following images show the condition for South West Kenya, which is the major agriculture region of Kenya.


Vegetation growth rate in south-west Kenya at the end of December: for 2003 (left image) – 2004 (middle image) – 2005 (right image)

Map of Africa 
Vegetation growth rate in south-west Kenya at the end of December compared to average situation for the same period

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