Urban Expansion in Arid Landscapes: Four Decades of Land Transformation and Metropolitan Growth in Riyadh

Urban expansion in arid environments remains insufficiently understood, particularly where growth occurs with limited competition for agricultural and vegetated land. This study examined long-term Land Use and Land Cover (LULC) change, land transformation, and urban expansion in Riyadh, Saudi Arabia, from 1985 to 2025 using multi-temporal Landsat imagery, Random Forest (RF) classification, and Google Earth Engine (GEE). Five decadal benchmark years were analyzed to quantify urban growth dynamics, land transition pathways, and spatial patterns of expansion. Built-up land increased from 250.06 km2 in 1985 to 1713.98 km2 in 2025, representing a net increase of 1463.92 km2 (585.42%). Expansion occurred predominantly through the conversion of barren desert land into built-up surfaces, while vegetation and water contributed comparatively little to urban land conversion. Temporal analysis additionally showed increasing absolute territorial expansion despite declining proportional growth rates in later decades, providing complementary evidence of changing growth dynamics as the metropolitan footprint enlarged. These findings characterize Riyadh as a context-specific expression of metropolitan growth in a hyper-arid setting, where extensive barren-land availability conditions the dominant land-transformation pathway. The study provides a reproducible framework for long-term urban monitoring and supports evidence-based urban management and planning in rapidly expanding arid cities.