Theoretical Modelling of Sahelian Rainfall Regime Shifts Under Anthropogenic Climate Forcing and Land Degradation Feedbacks in Northern Nigeria

The Sahel experienced one of the most dramatic rainfall regime shifts of the twentieth century, and northern Nigeria's climatological trajectory under compounding anthropogenic greenhouse gas forcing and land degradation feedbacks remains theoretically underdeveloped in the Nigerian literature. This study develops and applies a theoretical framework integrating general circulation model outputs, land surface scheme perturbation experiments, and observational diagnostics to examine the mechanisms and probability of future Sahelian rainfall regime shifts over northern Nigeria. CMIP6 ensemble outputs under SSP3-7.0 are analyzed alongside a series of WRF sensitivity experiments in which surface albedo and soil moisture are systematically altered to simulate progressive land degradation scenarios. The theoretical framework draws on nonlinear dynamical systems theory to characterize the potential for bistability between wet and dry rainfall regimes, assessing proximity to tipping points using early warning statistical indicators applied to NiMet long-term records. Results suggest that the observed post-1990s partial rainfall recovery in Sokoto and Katsina states represents a metastable wet regime state that may be vulnerable to reversal under continued land degradation, even absent further greenhouse gas increases. Original contributions include formalization of a land-climate feedback parameter specific to Nigerian Sahelian conditions and derivation of critical albedo thresholds beyond which runaway drying becomes self-sustaining. Findings advance theoretical understanding of West African climate dynamics and provide a rigorous basis for land degradation policy assessment under Nigeria's Great Green Wall program. Keywords: Sahel, rainfall regime shift, land degradation, tipping point, theoretical framework.