Settlement evolution and its drivers across contrasting topographic units: Evidence from Tajikistan's socio-economic transition, 1990–2022

Abstract Topography is a key factor in mountain settlement evolution, but its effects can vary with socio-economic conditions. This can create different trajectories in river valleys, hilly regions, and high mountains. Understanding how settlement evolution and associated factors differ across terrain zones is important for explaining spatial differentiation under socio-economic transition and informing terrain-sensitive planning. A case in point is Tajikistan. Its mountains, hills, and valley plains support distinctive settlement systems, while socio-economic transition since 1991 has accentuated their differences. Using land-cover, demographic, economic, topographic, hydrological, and transport-network data, this study traces settlement change in Tajikistan during 1990–2022. Terrain zoning, landscape-pattern metrics, and geographically weighted regression (GWR) identify national trends, terrain differences, and temporal changes in factors associated with settlement expansion. Two main findings emerge. First, the total area occupied by settlements increased over three decades, patch forms became more regular, and overall spatial aggregation declined. The form of expansion nevertheless varied sharply by terrain. Valley plains experienced predominantly contiguous outward growth; settlements in mountain-hill areas extended mainly in belts along piedmont zones; and high-mountain plateaus developed through scattered patches. Settlement size, shape complexity, and spatial aggregation declined in sequence from valley plains to mountain-hill areas and then to high-mountain plateaus. Second, population growth, economic development, conflict disturbance, and elevation were especially influential in the early transition period. In later years, road accessibility and the availability of flat land became the principal associated factors. Dominant influences shifted from population and economic growth to improved transport in valley plains; from elevation and population to flat land and transport in mountain-hill areas; and from the combined constraints of elevation and limited flat land to the joint influence of transport improvement and flat terrain on high-mountain plateaus. These findings provide evidence for understanding mountain settlement differentiation under complex terrain conditions.