R codes for implementing the river connectivity analysis

Dams are quintessential infrastructures in human civilization, providing indispensable services such as hydropower generation, irrigation, and flood mitigation. However, their construction is primarily responsible for disrupting the natural river flows, leading to accelerated decline and extinction of especially migratory aquatic species. This impact is evident in the Nile River Basin, where dams have increased in the Blue Nile, Equatorial Lakes and White Nile (Equatorial White Nile) sub-basins, albeit with limited understanding of their longitudinal connectivity. In this study, we used the Dendritic Connectivity Index (DCI) and Stream Continuity Index (SCI) to examine the temporal and spatial changes in the longitudinal connectivity of the Blue Nile Basin (BNB) (1925 to 2035) and Equatorial Lakes and White Nile (EWN) (1954 to 2035). We also evaluated the individual dam contribution to the fragmentation of river network connectivity. In the BNB, the DCI significantly reduced from 60.05% (SD±13.23) in 1925 to 20.48 % (SD±11.89) in 2035. SCI decreased from 60.64% (SD±14.76) in 1925 to 19.91% (SD±10.76) in 2035. This decline, predominantly affecting the middle and lower sections of the basin, was primarily contributed by the Grand Ethiopian Renaissance Dam (GERD). However, projections indicate that the proposed Karodobi Dam will significantly affect the connectivity by 2035. In the EWN, DCI significantly reduced from 55.05% (SD±2.05) in 1954 to 18.65% (SD±12.80) in 2035. SCI decreased from 55.04% (SD±1.67) in 1954 to 18.94% (SD±13.25) in 2035. The middle and lower sections of the basin were also the most disproportionately impacted regions, with the Karuma dam on the main River Nile playing a significant role. Projections indicate that by 2035, the Nabuyole falls dam on River Nzoia will substantially affect the connectivity. This study provides an early warning indicator to effectively plan for proposed dams, taking into account migratory aquatic species during dam construction. We also recommended a detailed development of a basin-wide database for barriers to understand the full extent and severity on the river network connectivity.