Building resilience of water infrastructure to cascading cross-border climate risks: a case study of Malawi’s drinking water infrastructure

Background Malawi’s water security depends on the Lake Malawi-Shire River system, which receives approximately 60% of its inflows from transboundary catchments in Tanzania and Mozambique. This dependence creates cascading cross-border climate risks that threaten downstream water infrastructure. The system exhibits threshold behavior at 474.1 m above sea level (asl), below which hydrological drought conditions emerge and outflows to the Shire River cease. Despite this documented vulnerability, existing policy frameworks exhibit critical gaps in transboundary coordination for climate risk management. Methods This study integrated policy analysis, hydrological analysis of 40 years of observational data (1970–2013), climate projections from 20 CORDEX-Africa regional climate models under RCP4.5 and RCP8.5 scenarios (2021–2050; 2071–2100), and semi-structured stakeholder interviews (n = 28 across four riparian states). Vulnerability assessment applied an exposure-sensitivity-adaptive capacity framework to Walkers Ferry Dam and associated drinking water infrastructure serving Blantyre, Malawi. Results Hydrological analysis confirmed the 474.1 m asl critical threshold, with each 1 °C temperature increase reducing mean lake level by 0.3 m and outflow by 17%. Forty-three cascading events were identified between 1990 and 2023, with Mann-Kendall analysis revealing significant trend acceleration (Tau = 0.48, p < 0.01). Drought intensity is projected to increase 25%–50% by 2021–2050 and 131%–388% by 2071–2100. Policy analysis identified severe gaps in transboundary coordination, data sharing, and cascading risk recognition. The 2024 high-water event at Walkers both drought-type illustrated both drought-type and flood-type cascading risks, demonstrating that extremes across the full hydrological spectrum disrupt downstream water abstraction for Blantyre. Conclusion Resilient water infrastructure in transboundary basins requires governance frameworks that explicitly address threshold behaviors, cascading risk propagation, and transboundary inflow dependencies. Adaptive infrastructure design, regional early warning systems, and formalized data-sharing protocols among riparian states are urgently needed. These findings have direct relevance for the Lake Malawi-Shire system and broader applicability across transboundary basins in sub-Saharan Africa.