RAPID: Measuring the Isotopic Fingerprint of the South American Summer Monsoon during a Strong El Nino, 2023-2024

Purdue University, West Lafayette IN

Investigators

Abstract

The western slopes of the Peruvian Andes are remarkable for the circuitous pathways over which moisture travels to get to the region and fall as rain or snow. Some moisture comes from the Amazon to the east, but much of the moisture is lost as Amazonian air ascends over the high mountains to reach the western slopes. Moisture also comes from the north, following the low-level jet that flows along the Cordillera from points in Colombia and Venezuela. Other pathways arrive from the south and east, in all cases profoundly shaped by the blocking and guiding effects of the mountains. Work conducted under this award considers the extent to which the source region and travel history of moisture can be determined by looking at the isotopic composition of rainwater collected in sites on the western side of the Peruvian Andes. Here isotopic composition refers to the relative abundance of water molecules containing deuterium, oxygen-17, or oxygen-18. Water molecules with heavier isotopes of hydrogen and oxygen evaporate more sluggishly and condense more readily, thus water vapor becomes depleted of heavier isotopes to the extent that precipitation occurs along its transport pathway. Previous work has shown promise for the use of isotopic composition as a marker for moisture pathways but these efforts did not adequately capture the isotopic signature of moisture originating in the eastern Pacific and moving upslope to the collection sites. The developing El Nino offers a promising opportunity to sample rainwater of Pacific origin, particularly as the peak of El Nino occurs in the December-to-February season and coincides with the South American Summer Monsoon. Also, the 2023/24 El Nino event is predicted to be as strong as the strongest events on record, thus the next few months may provide conditions that will not be repeated for a decade or more. The desirability of sampling under these conditions, with little time to perform the necessary organizational and logistical tasks to enable sampling, is the basis for making this award using the RAPID mechanism. The work is of societal as well as scientific interest given that the western Peruvian Andes is a region of limited water resources and thus susceptible to drought, as well as the mudslides and flooding that come with an overabundance of rainfall. The rainwater collection sites have been developed in collaboration with Peruvian colleagues including academics and local volunteers, and research findings will be disseminated within Peru. In addition, the project provides support and training to a graduate student and two undergraduates students are employed by the project. A further consideration is that a successful outcome would enable more general use of isotopic signatures as a way of understanding the hydrological cycle and validating model simulations of it. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.