The hydroclimatology of tropical South America is strongly coupled to low-frequency large-scale oceanicand atmospheric phenomena occurring over the Pacific and the Atlantic Oceans. In particular, El Niño–SouthernOscillation (ENSO) affects climatic and hydrologic conditions on timescales ranging from seasons to decades.With some regional differences in timing and amplitude, tropical South America exhibits negative rainfall andstreamflow anomalies in association with the low–warm phase of the Southern Oscillation (El Niño), and positiveanomalies with the high–cold phase. Such dependence is illustrated in the hydroclimatology of Colombia throughseveral empirical analyses: correlation, empirical orthogonal functions, principal component, and spectral analysis, and discussion of the major physical mechanisms. Observations show that ENSO’s effect on river dischargesoccurs progressively later for rivers toward the east in Colombia and northern South America. Also, the impactsof La Niña are more pronounc... Abstract The hydroclimatology of tropical South America is strongly coupled to low-frequency large-scale oceanicand atmospheric phenomena occurring over the Pacific and the Atlantic Oceans. In particular, El Niño–SouthernOscillation (ENSO) affects climatic and hydrologic conditions on timescales ranging from seasons to decades.With some regional differences in timing and amplitude, tropical South America exhibits negative rainfall andstreamflow anomalies in association with the low–warm phase of the Southern Oscillation (El Niño), and positiveanomalies with the high–cold phase. Such dependence is illustrated in the hydroclimatology of Colombia throughseveral empirical analyses: correlation, empirical orthogonal functions, principal component, and spectral analysis, and discussion of the major physical mechanisms. Observations show that ENSO’s effect on river dischargesoccurs progressively later for rivers toward the east in Colombia and northern South America. Also, the impactsof La Niña are more pronounc...

The knowledge of the annual cycle of rainfall is of primary concern for many socioeconomic activities such as agricultural planning, electricity generation, and flood and other disaster management. The annual cycle of rainfall in Colombia has been studied so far using monthly or quarterly information, identifying zones with the unimodal regime (one wet season and one dry season) over the Caribbean, the Amazon, and the Pacific regions and zones with the bimodal regime (two wet and two dry seasons) in the Andes. This paper explores the annual rainfall cycle in Colombia on a daily basis using historical records of 1,706 rain gauges and the Climate Hazards Group Infrared Precipitation with Station data precipitation data set. We found four types of annual precipitation regimes: unimodal, bimodal, mixed, and aseasonal. The unimodal regime predominates in the low‐altitude zones of the east and the north, the bimodal and mixed regimes over the Andes mountain range, and the aseasonal in the Pacific region. These results improve the statistical diagnosis of the spatial variability of the rainfall seasonality in Colombia. This phenomenon, however, is still far from being fully understood in its hydroclimatic context. The annual migration of the Intertropical Convergence Zone is not enough to explain the diversity of rainfall regimes in Colombia. Local factors such as topography and land cover could play an important role in the occurrence and duration of rainfall seasons.

Using hourly records from 51 rain gauges, spanning between 22 and 28 yr, the authors study the diurnal cycle of precipitation over the tropical Andes of Colombia. Analyses are developed for the seasonal march of the diurnal cycle and its interannual variability during the two phases of El Niño–Southern Oscillation (ENSO). Also, the diurnal cycle is analyzed at intra-annual time scales, associated with the westerly and easterly phases of the Madden–Julian oscillation, as well as higher-frequency variability (<10 days), mainly associated with tropical easterly wave activity during ENSO contrasting years. Five major general patterns are identified: (i) precipitation exhibits clear-cut diurnal (24 h) and semidiurnal (12 h) cycles; (ii) the minimum of daily precipitation is found during the morning hours (0900–1100 LST) regardless of season or location; (iii) a predominant afternoon peak is found over northeastern and western Colombia; (iv) over the western flank of the central Andes, precipitation maxima occur either near midnight, or during the afternoon, or both; and (v) a maximum of precipitation prevails near midnight amongst stations located on the eastern flank of the central Cordillera. The timing of diurnal maxima is highly variable in space for a fixed time, although a few coherent regions are found in small groups of rain gauges within the Cauca and Magdalena River valleys. Overall, the identified strong seasonal variability in the timing of rainfall maxima appears to exhibit no relationship with elevation on the Andes. The effects of both phases of ENSO are highly consistent spatially, as the amplitude of hourly and daily precipitation diminishes (increases) during El Niño (La Niña), but the phase remains unaltered for the entire dataset. We also found a generalized increase (decrease) in hourly and daily rainfall rates during the westerly (easterly) phase of the Madden–Julian oscillation, and a diminished (increased) high-frequency activity in July–October and February–April during El Niño (La Niña) years, associated, among others, with lower (higher) tropical easterly wave (4–6 day) activity over the Caribbean.