Terrain Controls on the Portability of Rainfall Prediction Models: A Framework for Transferability and Adaptability Across Tropical and Temperate Climates

Rainfall prediction models often lose skill when transferred across regions, particularly in data-sparse settings where local recalibration is not feasible. This study investigates whether topographically analogous landscapes exhibit consistent patterns of model portability in next-day rainfall occurrence prediction across contrasting climates. Random Forest and Logistic Regression classifiers trained on multi-year daily atmospheric data were evaluated across three hydrogeomorphic classes, Alluvial/Valley, Delta/Marsh, and Coastal Plain, using paired temperate sites in the United States and tropical sites in Malaysia. Portability was quantified using Transferability, representing a model’s ability to export predictive skill, and Adaptability, representing a site’s receptivity to externally trained models. Performance, sensitivity, and stability metrics were synthesized within a Behaviour Grid to support systematic interpretation. Results reveal a robust terrain-driven hierarchy: Delta/Marsh models are the strongest exporters, Alluvial/Valley sites the most adaptable receivers, and Coastal Plain sites are stable generalists. This general hierarchy is preserved across climates and years when evaluated using Area Under the Receiver Operating Characteristics Curve, indicating strong terrain structuring of portability, although fixed-threshold performance metrics show sensitivity to temporal variability. These findings indicate that terrain class provides a useful basis for evaluating cross-regional model transfer, supporting more informed regionalisation and deployment decisions across heterogeneous environmental settings.