In tropical South America, weather and climate are affected by the meridional oscillation of the inter- tropical convergence zone, the Pacific and Atlantic oceans, the Amazon basin, and the Andes Mountains. The dominant mode of the inter-annual climate variability in this region is the El Niño/Southern Oscillation (ENSO) phenomenon. Colombia is among the South American countries that experiences large climate anomalies because of ENSO. However, the hydrologic response in Colombia to a particular ENSO event is highly complex and non-linear. To describe the hydrologic response in Colombia, a one- way coupled atmospheric-land surface hydrologic modelling approach is implemented whose main components are Colorado State University’s Regional Atmospheric Modelling System (RAMS) and the Swedish Hydrologiska Byrans Vattenbalansavdelning-Hydrologic Modelling System (HBV-HMS). The system is implemented for seasonal simulations and for daily simulations. Seasonal simulations emphasize the annual cycle at regional scales, while daily simulations focus on describing the diurnal cycle for specific watersheds.
