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Hong Kong Polytechnic University (2018)

Modelling woody vegetation in Sudano-Sahelian zone of Nigeria using remote sensing

Usman, Muhammad

Titre : Modelling woody vegetation in Sudano-Sahelian zone of Nigeria using remote sensing

Auteur : Usman, Muhammad

Université de soutenance : Hong Kong Polytechnic University

Grade : Doctor of Philosophy (PhD) 2018

Résumé partiel
Rural areas surrounding Nigeria’s second largest city, Kano, in the northern Nigeria, have some of the highest rural population densities in the world, and these have been increasing rapidly in recent decades, with as yet, no signs of stabilising. The subsistence nature of livelihoods in this semi-arid region bordering the African Sahel zone, where rainfall is known to be highly variable, introduces considerable risk for crop and woody vegetation productivity. A scenario of recent high rural and urban population growth in and around the city of Kano, set in context of predicted temperature increase and greater rainfall variability due to climate change, may give cause for concern. As almost all rural, and the vast majority of urban households still use wood fuel for cooking, lighting and heating (although Nigeria is the world’s 6th largest oil producer), a return to the rainfall amounts of the drought decades of the 1970s and 80s could cause widespread economic and social distress. There are many accounts of rainfall trends in the northern Nigeria, many observing severe declines, and others a decline in recent decades followed by a return to normal. Almost all studies report great spatial variation in rainfall amounts and trends, with large differences in nearby areas, or conflicting results for the same regions. Furthermore, these reported statistics appear in many cases to be conflicting with farmers’ perceptions of rainfall trends and its effects on their lives and livelihood. This study evaluates the available sources of rainfall data over recent decades in the northern Nigeria, using both climate station data and satellite-based rainfall products, as satellite rainfall variables are spatially superior to point-based ground stations. These rainfall data are first compared with satellite-based vegetation indices NDVI products such as GIMMS 3g and MODIS, extending back several decades to the early 1980s. They are also compared with several satellite-based rainfall products such as ARC, CHIRPS, TARCAT and TRMM, covering the same decades. The second part of the study evaluates climatic impacts on the rural landscape and thus on the agricultural economy, specifically on farmland trees, which are used by farmers for fuelwood for own use as well as for sale to supplement farm incomes. This part of the study focuses on the "Kano Close Settled Zone", due to its high rural population density as a case study example for savanna Africa. It evaluates high resolution remotely sensed images for tree inventory and changes in woody biomass, in terms of tree density and species composition, in the intensively farmed parklands surrounding Kano City. The objective is to observe trends in the woody vegetation surrounding Kano City from the 1960s onwards, which may be related to climatic trends.

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