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Curtin University (2017)

Remote Sensing of West Africa’s Water Resources Using Multi-Satellites and Models

Ndehedehe, Christopher Edet

Titre : Remote Sensing of West Africa’s Water Resources Using Multi-Satellites and Models

Auteur : Ndehedehe, Christopher Edet

Université de soutenance : Curtin University

Grade : Doctor of Philosophy (PhD) 2017

The preponderance of evidence show that the warming of the climate system affects natural systems, leading to accelerations in the global hydrological cycle. In Africa, changes in the climate system have enormous impacts on freshwater resources, weather systems, agriculture, health, and much of the continent’s remarkable biodiversity. These impacts will continue to grow with negative consequences that will hamper economic development and demean the standard of living of the world’s poorest continent. Despite these deleterious impacts of climate variations, in West Africa, there are still considerable gaps however, in the knowledge of how global changes in climate impact on the region’s freshwater systems. Not only is hydrology poorly understood, the knowledge of large scale temporal and spatial dynamics in land water storage, and a suitable framework to characterize key hydrological metrics and extreme weather events are lacking. West Africa play key roles in global climate and shows one of the strongest variations in climatic conditions and water resources systems. As it turns out, the region is apparently under-represented in the literature when it comes to significant discussions on terrestrial hydrology. This prominent gap is largely precipitated by increasing number of constraints such as lack of considerable and robust investments in gauge measurements for meteorological and hydrological applications amongst other factors. To improve our contemporary understanding of West Africa’s terrestrial water systems and address the aforementioned issues, this thesis explored a suite of some relatively new remote sensing, global reanalysis, model, and satellite gravity data, to primarily investigate the spatio-temporal characteristics of terrestrial water storage (TWS). A new statistical-based framework to improve drought characterisation and the understanding of hydrological variability, physical characteristics, and the impacts of climate variability on eco-hydrological processes in West Africa is studied. This is achieved through a number of specific objectives that also employ, in addition, a range of multivariate techniques to analyse a suite of multi-resolution data and Gravity Recovery and Climate Experiment (GRACE) observations. This thesis outlines thoroughly documented protocols in the practical monitoring and comprehensive assessment of hydrological processes, influence of global climate and large reservoir systems on the regional dynamics of TWS. GRACE-TWS in West Africa is principally driven by rainfall unlike the Congo basin where river discharge provides the dominant control. A fourth-order cumulant statistics is introduced as novel method to support drought regionalisation and characterisation. Low frequency climate oscillations and quasi-periodic phenomena play key roles in drought characteristics and in the temporal and spatial distribution of West Africa’s TWS. Contemporary and complementary perspectives on GRACE-TWS hydrological controls on surface vegetation dynamics over West Africa are also presented. In practical terms, this thesis shows that GRACE observations will continue to provide considerable leverage and unparalleled perspectives in (i) large scale hydrological studies, (ii) assessing the impacts of global climate change, and (iii) evaluating ecosystem performance in West Africa. This research has ignited a plethora of scientific findings that are not only informative but instructive and useful for public policy and management decisions related to water resources.


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