Surface temperature variability in a tropical Andean summit: influence of ENSO, elevation, and slope direction

Abstract Tropical Andean ecosystems are critical for biodiversity conservation and water regulation. Climate change is affecting these ecosystems, but research at high altitudes is still scarce. We aim to understand the complex relationships between surface temperatures and seasons, El Niño Southern Oscillation phenomenon (ENSO), elevation, and slope direction, using novel in situ monitoring data in Northern South America (i.e., Cocuy National Park, Colombia). We analyzed hourly surface temperature data recorded from 2011 to 2019 at four summits between 4050 and 4400 m elevation, collected using self-logging thermometers as part of the Global Observation Research Initiative in Alpine Environments (GLORIA) Andes network. Furthermore, we assessed temperature trends and differences in relation to elevation, season, slope, and ENSO. Contrary to other regional results, surface warming in these summits did not increase with altitude i.e., no local evidence of elevation-dependent warming (EDW). Even more, minimum and maximum temperatures exhibited contrasting trends: minimum and maximum temperatures increased over time at the lowest elevation, while minima increased and maxima decreased at the highest elevation. Also, lower elevations warmed faster during the dry season. Surface temperatures were weakly correlated with the Oceanic Niño Index (ONI), and the other El Niño indices (1+2, 3 and 4). Given that the ONI index reflects both the effects of El Niño and La Niña, we observed that during La Niña there was a significant intensification of warming for minimum temperatures and cooling for maximum temperatures at the highest elevation. Slope orientation played an important role. Contrary to what other studies have found, minimum temperature trends on slopes exposed to predominant winds (i.e., northeasterlies) were significantly different (warmer) from the leeward slopes (cooler). These findings underscore the need for continued research and monitoring to better understand microclimate variability and heterogeneity in these complex topographic regions. Such efforts are essential for improving climate model accuracy and guiding effective natural resource management in the face of a changing climate.