The importance of terrestrial moisture sources for precipitation in Colombia: a combined isotopic and modelling approach

Abstract

ABSTRACT: The hydroclimatology of Northern South America is directly associated with the coupled dynamics of oceanic and terrestrial surface-atmosphere exchange, as moisture sources derived from these two sources interact to produce rainfall in the mountainous areas of the Andes. However, the relative contribution of these two sources, as well as their temporal dynamics have been described only through modeling studies, and no observational tools have been used to corroborate these results. The study of moisture sources through stable isotopes analysis has been a common approach to understand the changes in the water cycle and dynamics of climate, as its allows tracking the connection between evaporation, transpiration and precipitation, as well as the influence of large scale hydroclimatic phenomena, such as the seasonal migration of the InterTropical Convergence Zone (ITCZ). In this study, we characterize the isotopic composition of moisture sources becoming precipitation in the Northern Andes and the Caribbean regions of Colombia, using information of stable isotopes in precipitation (δ18O, δ2H) from the Global Network of Isotopes in Precipitation (GNIP) (1971-2016) and contrast them with results from the Lagrangian FLEXPART model that uses input from ERA-Interim reanalysis. Our results indicate that most precipitation in the region comes from terrestrial sources including recycling (>30% monthly all year), the northern Amazon (up to 17% monthly for June, July and August) and Orinoquia (up to 28% monthly for April) basins; followed by oceanic sources such as the Tropical South Pacific (up to 30% monthly in October, November, December) and Tropical North Atlantic (up to 30% monthly for January). Our results highlight the utility of stable isotopes in precipitation to discriminate terrestrial and oceanic sources of precipitation. More generally, our results indicate the previously overlooked hydrological coupling between terrestrial ecosystems in Northern South America, which highlights that the potential impacts of current rates of land use transformation in the region can also express in other areas of the continent, and include aspects previously overlooked such as atmospheric moisture transport and hydrological consequences in a country like Colombia where, for example, rainfed agriculture and hydropower generation support an important proportion of the nation’s economy.