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CASE STUDY 9 : Influence of El Niño on the vegetation status

 

The rainfall intensity at the end of 2009 and the beginning of 2010 (until May) is influenced by the El Niño event. The influence of this event on the vegetation status can easily be studied with the ENDELEO tools.

According to the Kenya meteorological department, most parts of the country received enhanced rainfall that was well distributed both in time and space during March-April-May 2010. This was the case for the northwest, west, central and northeast parts of the country where most meteorological stations recorded rainfall that was well above 100 percent of their seasonal Long-Term Means (LTMs) for March and May.

The heavy and continuous rainfall impacted positively on the agricultural, water resource, live stock, energy and other rainfall dependent sectors. However, there was a negative impact on disaster management since floods and landslides/mudslides that occurred in different parts of the country claimed several human lives, washed away minerals and livestock, destroyed property worth millions of shillings and displaced many people.

The ENDELEO graph tool allows to study the respons of the vegetation to these heavy rainfalls in for example the northwestern districts Marsabit, Isiolo, Samburu and Turkana.
The evolution of the NDVI or ‘vegetation health and density’ is plotted against the average situation for all land cover types in these four districts.  

case9.1

Situation of the northern districts Marsabit, Isiolo, Samburu and Turkana in Kenya.

 

case9.2
Vegetation health and density for the total area of Marsabit for 2010 smoothed and for the average year smoothed.

case9.3
Vegetation health and density for the total area of Turkana for 2010 smoothed and for the average year smoothed.

case9.4
Vegetation health and density for the total area of Isiolo  for 2010 smoothed and for the average year smoothed.

case9.7
Vegetation health and density for the total area of Samburu for 2010 smoothed and for the average year smoothed.

When reviewing these four graphs, the influence of the weather conditions on the status of the vegetation in the area can be measured. In the four districts, the high amount of rain resulted in an increase of the NVDI values during the months March, April and May. The smoothed blue graph for 2010 is located above the black graph representing the smoothed average NDVI. A higher density of the vegetation is occurring when El Niño is present. The earlier onset of the long rainy season is visible as an earlier increase of the NDVI. The shift between the blue and black graph is clear for all districts. The long rainy season starts this year somewhere half of February, whereas this normally occurs in half March.

The Kenyan meteorological department predicts for the short rainy season (October – November – December) that much of the country is likely to experience generally depressed rainfall. The expected depressed seasonal rains are associated with the presence of an evolving La Nina. You may follow up possible effects on the vegetation with the ENDELEO tools.

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