An Original Theoretical Framework for Soil Degradation Trajectory Modelling in the Lake Chad Basin Dryland Fringe, North East Nigeria

This dissertation develops an original theoretical framework for modelling soil degradation trajectories in the dryland fringe of the Lake Chad Basin, Borno and Yobe States, Nigeria's North East geopolitical zone. Existing land degradation assessment frameworks inadequately capture the complex non-linear dynamics of soil degradation in semi-arid systems subject to combined pressures of climate change, land use intensification, insecurity-driven abandonment, and ecological tipping point processes. The dissertation employs a four-component approach: systematic analysis of historical land cover and soil change using multi-temporal satellite data (Landsat 1975 to 2023), collection of a 15-year retrospective soil monitoring dataset from archived samples and paired new sampling at 60 sites, development of a systems dynamics model incorporating coupled climate, vegetation, soil, and land use feedback loops, and Bayesian calibration of model parameters against observed degradation trajectories. Field data on soil texture, organic carbon, crusting, saltation threshold, and biological soil crust cover provide model inputs. The dissertation proposes the Lake Chad Dryland Soil Trajectory Model (LCDSTM) as an original contribution, which explicitly models three degradation regimes (linear slow degradation, threshold-mediated rapid degradation, and catastrophic state shift) and predicts transition probabilities between regimes as functions of rainfall variability and land use intensity. The LCDSTM is the first soil degradation model parameterised specifically for the Lake Chad Basin margin and provides a scientifically rigorous basis for designating intervention priority zones under Nigeria's Great Green Wall implementation. Keywords: soil degradation trajectory, Lake Chad Basin, systems dynamics model, semi-arid, dryland fringe.