Intellectual Merit

We set out to reconstruct past hydroclimatic variability over Mainland Southeast Asia using multiple proxy datasets derived from speleothems and tree-rings, and to compare and calibrate the δ^1⁠8O records from these two proxy sources. This approach enhanced our ability to investigate the dynamics of Asian monsoon precipitation variability in response to external forcing (e.g., solar), and to natural internal variability governed by coupled ocean-atmosphere processes, such as ENSO. In addition, we sought to investigate how temperature, precipitation, and precipitation isotopic signals are incorporated in each of our respective archives, so that we might better determine whether local and regional climate signals are synchronous or reflective of systematic differences linked to each proxy. We also compared our tree-ring derived hydroclimate indices from Vietnam cypress with a lake sediment δ^1⁠8O record from northern Vietnam, and demonstrated a coherence in decadal variability for all of the major droughts and pluvials identified in our prior work. The lake sediments, however, allowed for retention of centennial trends in hydroclimate variability that was not possible from tree rings alone, demonstrating the importance of multiple proxy sources. For this project we developed several new δ^1⁠8O records from existing tree-ring site collections, and used these data for a vastly improved reconstruction of streamflow from the Chao Phraya River, owing to the ability of the stable isotope records to record peak flow. We have expanded this research to a novel way of reconstructing seasonally-discrete streamflow using an improved version of the Monsoon Asia Drought Atlas, and this research continues beyond the current project. We are also continuing with monitoring and analyses of the isotopic variations in rainfall, soil water, cave drip water and for speleothems and tree rings. The research conducted for this project has led to several exciting new avenues for future endeavors.

Broader Impacts

Project PIs traveled to Laos and Vietnam for collection of speleothem and tree ring samples, and during these visits we held two well attended, international workshops at Bidoup Nui Ba National Park in Vietnam. In January 2019 we held Stable Isotopes in the Environment, which was attended by PIs Johnson, Griffith and Buckley, and participants from several countries including the U.K., Australia, Singapore and the USA. In January 2020 we held the first official meeting of the Southeast Asian Paleo Environments Consortium (SAPEC-2020), which was organized by PI Buckley and very well attended by professors and students from multiple countries, with several hands-on instructional sessions. In 2018 we held similar sessions in Laos for the tree ring work in the Nakai Nam Theun region for the work on the rare water pines. From a data standpoint, we have produced a series of robust streamflow reconstructions that include peak season and base flow seasons, and these data will be very useful for regional hydro planning and a variety of other applications. Several graduate student projects were developed during these workshops, especially for Vietnamese students working with project PI Buckley on dendroclimatology and tree ecophysiology within the Annamite Range. This research will form the basis of a course taught by Buckley at Dalat University as part of a Fulbright Award for spring semester 2022 - Predicting the effects of Climate Change on Vietnam's Forests. 

Last Modified: 05/07/2021
Modified by: Brendan M Buckley