Geospatial analysis and prediction of urban growth along the Colombo Kandy road corridor in Sri Lanka using the SLEUTH model

This study presents a geospatial assessment of historical and projected urban growth along the Colombo–Kandy A1 Road corridor in Sri Lanka using multi-temporal Landsat imagery, urban growth indices, and the SLEUTH urban growth model. Supervised land-use classifications achieved high reliability, with overall accuracies ranging from 92.5% to 97.5% and Kappa coefficients between 0.90 and 0.97 across all years. Historical urban dynamics were quantified using the Annual Urban Expansion Rate (AUER), Urban Expansion Intensity Index (UEII), and Urban Expansion Differentiation Index (UEDI), revealing concentrated growth in the Western Province. Colombo’s urban area increased from 9.58 km² in 1992 to 16.90 km² in 2024, while Kaduwela expanded from 0.26 km² to 37.78 km², representing the most rapid suburban transformation along the corridor. AUER values in the Western Province exceeded 1.0 during peak growth periods (1997–2002 and 2022–2024), with a temporary slowdown between 2007 and 2011. The SLEUTH model was calibrated using diffusion (5), breed (5), spread (10), slope resistance (95), and road gravity (5) coefficients, indicating terrain-constrained urban expansion with limited road-driven dispersion. Model projections suggest continued growth through 2050, with total urban area increasing to 478.26 km², compared to 336.45 km² in 2024 and 21.28 km² in 1992. High and highest probability growth zones are concentrated in Colombo and Gampaha districts, while expansion remains moderate in Kegalle and constrained in Kandy due to topographic resistance. The results provide spatially explicit evidence to support sustainable land-use planning, infrastructure prioritization, and corridor-scale development management along Sri Lanka’s most important inland transport axis.