Despite the heavy regional rainfall and considerable discharge of many rivers into the Colombian Basin, there have been few detailed studies about the dilution of Caribbean Surface Water and the variability of salinity in the southwestern Caribbean. An analysis of the precipitation, evaporation and runoff in relation to the climate variability demonstrates that although the salt balance in the Colombian Basin overall is in equilibrium, the area south of 12°N is an important dilution sub-basin. In the southwest of the basin, in the region of the Panama-Colombia Gyre, Caribbean Sea Water is diluted by precipitation and runoff year round, while in the northeast, off La Guajira, its salinity increases from December to May by upwelling. At the interannual scale, continental runoff is related to El Niño Southern Oscillation, and precipitation and evaporation south of 12°N are related to the Caribbean Low Level Jet. During El Niño years the maximum salinification occurs in the dry season (December-February) while in La Niña years the maximum dilution (or freshening), reaching La Guajira Coastal Zone, occurs in the wet season (September-November).

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La Guajira upwelling system has shown a moderate cooling (∼−0.05°C dec−1) over the period 1982–2014 for the months with strong upwelling (JFM). This contrasts with the general warming observed for most of the Caribbean region (∼0.25°C dec−1) over the same period. Cooling is in good agreement with the upwelling increase (∼0.04 m2s−1dec−1) observed in the region during winter months, although the position of the peaks in upwelling and SST trends does not coincide exactly due to the presence of the Caribbean Coastal Undercurrent.