Warming Trends in Basin‐Scale Heatwaves Across Ethiopia: An Observational Analysis Using Crossing Theory

ABSTRACT This study investigates the intensification of heatwaves across Ethiopia's major river basins from 1987 to 2024, employing crossing theory to analyse daily maximum temperature data. Basin‐scale dynamics, modulated by large‐scale climate teleconnections, primarily drive the observed trends. Defined as runs of three or more consecutive days exceeding basin‐specific 90th percentiles during the October–January dry season, heatwave frequency has increased by 150% since the 1990s. Lowland basins, particularly the Awash and Wabi Shebelle, now face near‐permanent heatwave conditions, with critical thresholds for infrastructure (28°C), agriculture (30°C), and health (35°C) being surpassed fivefold. Urbanization exacerbates these trends by 40%, primarily through nocturnal warming, while highland areas warm at a rate of 0.3°C per decade, contradicting global cooling expectations. The spatial pattern of intensification—strongest in southeastern basins—aligns with the known influence of the Indian Ocean Dipole on Horn of Africa climate, suggesting a teleconnective modulation of local thermodynamic drivers. This research introduces an innovative framework for establishing elevation‐adjusted thresholds, enhancing early‐warning systems for heat‐related impacts. The findings underscore the urgent necessity for climate‐resilient infrastructure and agricultural practices in Ethiopia and similar tropical highland regions, highlighting the critical intersection of climate change and societal vulnerability.