Twenty years of Kilimanjaro observations across 5000 m reveal tropical elevation-dependent warming under clear-sky conditions

Abstract Mountain regions are experiencing rapid climate change. However, temperature trends along elevation gradients remain poorly understood in the tropics, where long-term high-elevation air temperature ( T air ) observations are sparse. Here, we examine elevation-dependent warming (EDW) on Mount Kilimanjaro by combining a unique long-term in situ T air transect with Moderate Resolution Imaging Spectroradiometer (MODIS) land-surface temperature (LST), surface and topographic datasets. Using machine learning, we map clear-sky T air at four MODIS overpasses at 1 km resolution for 2004–2024. The models showed strong predictive performance, with RMSE values of 1.76 °C and 1.36 °C, and R 2 values of 0.94 and 0.95 for daytime and nighttime models, respectively. Modelled T air reveals strong diurnal contrasts: daytime T air shows strong spatial variability affected by radiation and surface properties, while nighttime T air varies more gradually with elevation. Trend analysis (2004–2019) identifies EDW under clear-sky conditions. Daytime trends become positive near the summit (+0.05 to +0.10 °C/decade), while strongest cooling occurs at 3000–3500 m (−0.13 to −0.14 °C/decade), coinciding with vegetation and land-cover change. Nighttime weak warming dominates most elevations (+0.04 to +0.15 °C/decade), while the summit remains near-neutral. These contrasts indicate that EDW on Kilimanjaro is shaped not only by elevation-dependent climate responses, but also by vegetation and land-cover changes that modify local surface-atmosphere coupling.