Structural Vulnerability of Cross-Border Bridges to Climate-Induced Hydrological Changes in East Africa

Cross-border bridges in East Africa occupy a uniquely critical and uniquely vulnerable position in the regional transport network: they are irreplaceable strategic assets connecting EAC member states, yet they must withstand river flow regimes that are being systematically altered by anthropogenic climate change without the benefit of the seismic or structural codes that typically govern the design of comparable infrastructure in higher-income settings. This study presents a comprehensive assessment of the structural vulnerability of 18 cross-border bridges at eight international border crossings in East Africa spanning the Kenya–Uganda, Kenya–Ethiopia, Uganda–South Sudan, Tanzania–Rwanda, and Tanzania–Burundi borders — to projected climate-induced hydrological changes over the period 2025–2075. A novel Climate-Structural Vulnerability Framework (CSVF) is developed, integrating: (i) stochastic hydrological modelling using CMIP6 precipitation projections under RCP 4.5 and RCP 8.5 scenarios to derive updated flood frequency curves for each river crossing; (ii) bridge scour analysis using the HEC-18 abutment and pier scour equations calibrated with field-measured bed material properties; (iii) time-dependent structural reliability analysis incorporating scour-induced foundation degradation and its effect on load-carrying capacity; and (iv) a composite Climate Vulnerability Index (CVI) integrating hazard, exposure, adaptive capacity, and institutional dimensions across a six-dimensional radar chart framework. Results show that under RCP 8.5, the 100-year flood discharge at the study crossings increases by 38–61% relative to historical values by mid-century, causing scour depths at existing foundations to exceed the critical threshold of 2.0 m at 11 of 18 bridges. The probab