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Lund University (2012)

MODIS NDVI satellite data for assessing drought in Somalia during the period 2000-2011

Alwesabi, Mohammed

Titre : MODIS NDVI satellite data for assessing drought in Somalia during the period 2000-2011

Auteur : Alwesabi, Mohammed

Université de soutenance : Lund University

Grade : Master 2012

This thesis studied the drought monitoring and assessing in Somalia environment during the period 2000-2011 with more details about the drought in 2010- 2011. Time series analysis of remote sensing data as well as rainfall data were used to achieve the aim of the study. Most of Somalia is located in dry zone with only some grass and pasture valid only pastoralism which is practices by half of the population. The country is frequently exposed to drought, occurring moderately every 3-4 years and severely every 7-9 years. Drought is characterized as a slow process, can happen everywhere and anytime and prolongs from months to years. The advance in remote sensing data both spatially and temporally makes it possible to use this data for drought monitoring regionally and globally. MODIS NDVI satellite data was used mainly to achieve the purpose of the study. The analysis was done at pixel-scale in seven locations as well as at regional-scale. To monitor and assess drought, three components were studied : onset, duration, and severity or intensity. The first important result is that among all drought years during the study period, the drought in 2010-2011 was the worst as it continued for longer time than previous droughts during the study period (around 12 months). In most parts in southern Somalia, there was extreme drought where the percent of negative change reached up to 30-50% below the normal. The impact of this drought was catastrophe because of existence of three factors which are the conflict in the country, nature of livelihood (pastoralism), and the population density. Drought often starts in Deyr season and continues to the Gu season in the next year e. g. 2003-2004, 2005-2006 and 2010-2011 and it is often followed by above normal rainfall. Also, droughts with long duration are lower frequent than that with short duration. The monthly correlation between rainfall and NDVI was significant in most parts of the country and surrounding areas, though not very strong (r 0.40). This relationship got higher with time lag one month for NDVI. The correlation in the second rainy months was found to be higher than the first rainy months with almost no correlation. Annual correlations were very low and even negative. Finally, remote sensing data proved to be a significant tool in monitoring and detecting drought components. In the thesis’s case where rainfall data and other meteorological data were absence or unreliable, remote sensing data was the only practical choice

Mots Clés  : remote sensing, vegetation index, drought, Somalia, geography, physical geography


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