Climate Change Adaptation in Nigerian Plant Disease Management: A Systems Modelling Approach to Projecting Future Disease Burden and Policy Interventions

Climate change will alter the epidemiology of major crop diseases in Nigeria through direct effects on pathogen physiology, vector population dynamics, host susceptibility, and cropping system structure. Quantitative projections of future disease burden and their policy implications are absent for the Nigerian national agriculture system, representing a critical gap in climate adaptation planning. This doctoral research develops an integrated systems modelling approach to project future disease burden for Nigeria's five most economically significant crop pathosystems: cassava mosaic disease, tomato late blight, maize stem rust, rice blast, and groundnut aflatoxin contamination. The modelling framework integrates: process-based epidemiological models for each pathosystem, parameterised from empirical field data collected across Nigeria's six geopolitical zones; climate downscaling from CMIP6 model ensembles under SSP2-4.5 and SSP5-8.5 scenarios; a cropping system adaptation module simulating farmer and policy responses to changing disease pressure; and economic impact assessment through partial equilibrium agricultural market modelling. Uncertainty quantification and scenario analysis are central components of the analytical design. The dissertation makes original theoretical contributions by introducing a novel framework for cross-pathosystem disease burden aggregation at national scale, and by developing a publicly accessible decision support tool for climate adaptation planning in plant health policy. Model projections for 2050 indicate that rice blast and groundnut aflatoxin contamination risks will increase under all climate scenarios, while late blight risk will decrease in lowland zones and increase on highland systems, with important implications for national plant health resource allocation. Keywords: climate change, disease modelling, plant disease burden, Nigeria, adaptation policy.