Urban Encroachment into Irrigable Lands: A 32-Year Spatiotemporal Analysis of the Sikta Command Area, Nepal

Abstract

Irrigation command areas in peri-urban regions of South Asia are increasingly threatened by land conversion to built-up uses, yet most irrigation planning continues to assume static land cover. This study presents a comprehensive spatiotemporal analysis of Land-Use/Land-Cover (LULC) change within the 47,431-ha command area of the Sikta Irrigation Project (SIP) in Nepal over a 32-year horizon (2000–2032). Using International Centre for Integrated Mountain Development (ICIMOD) LULC datasets (2000–2022) and GIS-based spatial modelling, we quantified historical changes in built-up and agricultural areas and projected future urban expansion to 2032 using a Compound Annual Growth Rate (CAGR) model coupled with proximity-based allocation. Our results show that built-up area increased from 460.80 ha in 2000 to 2,650.01 ha in 2019, representing a CAGR of 9.64%. Projections indicate that by 2032, built-up area will reach 8,771.33 ha, consuming an additional 6,121.32 ha of agricultural land. Consequently, the effective Culturable Command Area (CCA) is expected to decline from 41,783.53 ha (2019) to 35,662.21 ha (2032) – a cumulative loss of 8,367.21 ha since 2000. Spatial allocation reveals that urban expansion is concentrated along the East-West Highway and secondary road corridors, fragmenting the remaining agricultural landscape. These findings demonstrate that the Detailed Project Report (DPR) assumption of 90% GCA cultivability is no longer valid. We argue for mandatory periodic LULC monitoring and the integration of dynamic land-use projections into irrigation system planning.