Landslide timing and rainfall regimes in a rapidly urbanizing tropical mountain valley in Colombia

Rainfall-triggered landslides are a common natural hazard in the Colombian Andes, where they have caused both human and economic losses. We investigate the relationship between rainfall patterns and reported landslide occurrences in the rapidly urbanizing Aburrá Valley, northern Colombian Andes, over the course of hours to decades. We intersect data from rainfall radar and gauge records with catalogues of time-stamped landslides, and explore how yearly, monthly, and daily rainfall variations influence the timing of reported landslides. We find that La Niña phases of the El Niño-Southern Oscillation (ENSO) significantly increased rainfall, particularly during otherwise dry periods, thus raising soil moisture levels before the onset of rainy seasons. We also observe a distinct bimodal annual rainfall regime, with both the highest rainfall and landslide activity from April to June (AMJ) and September to November (SON). Finally, diurnal rainfall exhibits distinct afternoon convective peaks and prolonged nocturnal rainfall, which together predispose hillslopes to failure. Anthropogenic influences, such as unregulated construction and altered drainage systems, also compromise the stability of urbanized slopes. Our study underscores the need for rainfall-based early warning systems that account for oscillations in decadal, annual, and daily rainfall, as well as anthropogenic drivers to address landslide hazards effectively in this dynamic urban area, and similar ones in tropical mountains.