Drivers of convection initiation in the Tropical Andes

Abstract. Severe convective events are among the leading causes of weather-related damages in the Tropical Andes. Such events, often spanning thousands of square kilometers, are governed by a combination of local and synoptic-scale processes that together create favorable conditions for atmospheric convection. Understanding these processes and conditions is essential for improving forecasting of convection initiation, impact assessment, and risk management. Here, we investigated the regional atmospheric and land surface conditions associated with convective events using remote sensing, climate reanalysis, and environmental variables. We considered local land surface characteristics (e.g., vegetation, land surface temperature, and topography), together with background atmospheric conditions, including wind speed and direction, atmospheric instability, and the occurrence of low-level jets (LLJs) in the eastern Tropical Andes, where multiple severe convective events may occur within a single day. We analyzed the atmospheric conditions preceding 111,239 convective initiation (CI) events identified from infrared satellite imagery. We found that CI occurs most frequently between September and May, peaks in the early afternoon, and that roughly three-quarters of CI events (72 %) were associated with LLJs. Topographic gradients are strongly associated with CI in the high and low Andes. Vegetation and CAPE show no significant link with CI occurrence. CI tends to develop over warm surface anomalies with cooler conditions downwind, and near-surface flow dominated by NW, N, NE, and E winds. Once convection initiates, the subsequent precipitation peaks roughly 4–6 hours after CI and is strongly modulated by low-level wind direction and the presence of LLJs. Events associated with the Central and Andes Jets, when near-surface winds are predominantly from the N, NE, and E, produce nearly 3 times more precipitation than cases with NW flow or no LLJ. Interestingly, this enhanced precipitation tends to be more long-lived and moderate in intensity, rather than occurring in brief, extreme bursts. These findings highlight the importance of land–atmosphere interactions and regional atmospheric dynamics for severe convection in tropical–temperate transition regions, with direct implications for improving weather forecasting.