The importance of continental evaporation for precipitation in Colombia: A baseline combining observations from stable isotopes and modelling moisture trajectories

Abstract

AbstractThe hydroclimatology of Northern South America responds to the coupling between the Pacific and Atlantic oceans, the Amazon–Andes interactions, and the orographic barrier of the regional Andes. The relative contributions of oceanic and terrestrial moisture sources have been mostly evaluated in modelling studies, with limited observational data for validation. We combine observations from stable isotopes in precipitation and output from the Lagrangian moisture trajectory tracking model FLEXPART to characterize and contrast the relative contribution of oceanic (from the Atlantic and the Pacific) and terrestrial (from different regions in the continent) moisture sources to mean monthly precipitation in the Andes and Caribbean regions of Colombia. Our results indicate that most moisture becoming rain in the region has an atmospheric residence time that deviates from commonly assumed 10 days. These residence times vary between source and sink regions from 1 day in the case of recycling to more than 10 days in Andean precipitation originating in the Atlantic Ocean. Common integration times for both regions from all sources are commonly in the order of three to 7 days. Most precipitation in the region comes from terrestrial sources including moisture recycling from the same region (>30% for all months), the Orinoco River basin (up to 28% in April), and the northern Amazon basin (up to 17% in June, July, and August); followed by individually considered oceanic sources including the Tropical South Pacific (up to 30% monthly in October, November and December) and Tropical North Atlantic (up to 30% monthly for January). The fact that a significant proportion of rainfall is recycled highlights that water availability in the Andean and Caribbean regions of Colombia could potentially be altered by current widespread and pervasive changes in vegetation cover. More generally, our results highlight the need to assess the hydrological consequences of land cover change in South America, particularly in a country like Colombia where water, food, and energy security all depend directly on precipitation.