Inequities in the impacts of compound precipitation extremes on global transportation infrastructures in the late 21st century

The impact of compound climate extremes on transportation infrastructure is destructive and long-lasting, yet it remains unclear whether these impacts are equitably distributed across countries with different income levels. This study assesses global inequalities in exposure to compound precipitation extremes (CPEs), defined as the concurrent occurrence of short-duration, high-intensity 1-day precipitation (RX1D) and prolonged 5-day precipitation (RX5D), in the late 21st century under multiple climate scenarios. Under SSP585, approximately two-thirds of global transportation infrastructure is projected to experience increased exposure, affecting about 12.6 million km, with at least a 25% reduction in joint return periods, indicating more frequent extremes. Most exposed assets are concentrated in the Global North (10.9 vs. 1.3 million km in the Global South), with the largest absolute exposure in high-income regions (4.9 vs. 0.6 million km in lower-income regions). In contrast, adaptation needs show a clear inverse income gradient. Low-income countries require the highest safety factors (mean 1.31 for 50-year events), followed by lower-middle (1.20), upper-middle (1.17), and high-income (1.15) countries. This pattern remains robust across scenarios and infrastructure types (except motorways), revealing systematic inequality and underscoring the need for income-sensitive adaptation strategies in future infrastructure planning.