Montane forests are among the most critical terrestrial biodiversity reservoirs, acting as climate-regulating systems and water towers, and are vital for human well-being across the world. However, they are facing diverse, repeated, and contradictory challenges due to climate variability and change that may undermine their resilience. This study analyzed spatiotemporal trends in temperature and rainfall in the Aberdare Forest ecosystem, Kenya, over the past three decades (1994–2024). ERA5-Land (temperature, 9 km resolution) and CHIRPS-v3 (precipitation, 5 km resolution) provided the gridded climate datasets and were validated against observed station data from the Kenya Meteorological Department (KMD). Trend detection utilized the non-parametric Mann–Kendall (MK) test, while Sen’s slope estimator quantified the magnitude and direction of change. Results show a statistically significant positive trend in temperature, while rainfall demonstrated a statistically non-significant positive trend over the study period. Spatial analysis revealed statistically significant warming across the forest, bamboo, and moorland ecological zones, while rainfall showed positive but non-significant trends, with the magnitude of both temperature and rainfall trends varying across zones. These findings provide robust empirical evidence of significant temporal and spatial warming with no clear corresponding directional change in rainfall, underscoring increasing climate pressures on the Aberdare Forest ecosystem. The results establish one of the first empirically validated long-term climate trend baselines for the Aberdare Forest ecosystem. This benchmark provides critical evidence to inform adaptive governance and responsive management for enhanced resilience of East Africa’s montane forests.