The Importance of Continental Evaporation for Precipitation in Colombia:
A Baseline Combining Observations from Stable Isotopes and Modeling
Moisture Trajectories
Abstract
The hydroclimatology of Northern South America responds to
strongly-coupled dynamics of oceanic and terrestrial surface-atmosphere
exchange, as moisture evaporated from these sources interact to produce
continental rainfall. However, the relative contributions of these two
source types through the annual cycle have been described only in
modeling studies, with no observational tools used to corroborate these
predictions. The use of isotopic techniques to study moisture sources
has been common in assessing changes in the water cycle and in climate
dynamics, as isotopes allow tracking the connection between evaporation,
transpiration, and precipitation, as well as the influence of large
scale hydroclimatic phenomena, such as the seasonal Inter Tropical
Convergence Zone migration. We characterize the isotopic composition of
moisture sources becoming precipitation in the Andes and Caribbean
regions of Colombia, using stable isotopes data (δ18O, δ2H) from the
Global Network of Isotopes in Precipitation (1971-2016) and contrasting
it with moisture trajectory tracking from the FLEXPART model, using
input from ERA-Interim reanalysis to compute the relative contribution
of oceanic and terrestrial sources through the annual cycle. Our results
indicate that most precipitation in the region comes from terrestrial
sources including recycling (>30 % for all months),
Orinoco (up to 28 % monthly for April), and the northern Amazon (up to
17 % monthly for June, July, and August); followed by oceanic sources
including the Tropical South Pacific (up to 30 % monthly in October,
November, December) and Tropical North Atlantic (up to 30 % monthly for
January). These outcomes highlight the utility of combining stable
isotopes in precipitation and modeling techniques to discriminate
terrestrial and oceanic sources of precipitation. Further, 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. .