Droughts, Pluvials, and Wet Season Timing Across the Chao Phraya River Basin: A 254‐Year Monthly Reconstruction From Tree Ring Widths and δ18O

• Published in: Geophysical research letters Vol. 49; no. 17
• Main Authors: Nguyen, Hung T. T., Galelli, Stefano, Xu, Chenxi, Buckley, Brendan M.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 01.09.2022; Wiley
• Subjects: Annual; Catchment area; Climate change; Climatic analysis; dendrochronology; Discharge measurement; Drought; Gaging stations; Heterogeneity; high resolution paleoclimatology; Hurricanes; Hydroelectric power; Hydrologic data; Hydrologic drought; Hydrology; Irrigation water; Isotope ratios; Isotopes; Monsoon rainfall; monsoon timing; Monthly; Oxygen; Oxygen isotope ratio; Oxygen isotopes; Rainy season; Risk analysis; River basins; River discharge; River flow; Rivers; Seasons; stable oxygen isotope; Stream discharge; Stream flow; Streamflow data; streamflow reconstruction; Tree rings; Trees; Tributaries; Typhoons; Variability; Water discharge; Water management; Weekly; Wet season; Width; Thailand; Chao Phraya River
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2022GL100442

Water system operations require subannual streamflow data—e.g., monthly or weekly—that are not readily achievable with conventional streamflow reconstructions from annual tree rings. This mismatch is particularly relevant to highly seasonal rivers such as Thailand's Chao Phraya. Here, we combine tree ring width and stable oxygen isotope ratios (δ18O) from Southeast Asia to produce 254‐year, monthly‐resolved reconstructions for all four major tributaries of the Chao Phraya. From the reconstructions, we derive subannual streamflow indices to examine past hydrological droughts and pluvials, and find coherence and heterogeneity in their histories. The monthly resolution reveals the spatiotemporal variability in wet season timing, caused by interactions between early summer typhoons, monsoon rains, catchment location, and topography. Monthly‐resolved reconstructions, like the ones presented here, not only broaden our understanding of past hydroclimatic variability, but also provide data that are functional to water management and climate‐risk analyses, a significant improvement over annual reconstructions. Plain Language Summary Long records of river discharge, reconstructed from tree rings, help us understand how rivers behaved in response to past climates, and place projected climate changes in a broader perspective. While this knowledge is valuable, streamflow reconstructions have rarely been used to directly inform water management models, because tree rings are annual while water system models require streamflow data of higher resolutions, such as monthly or weekly. In our study, we use a rich network of tree ring data, consisting of both ring widths and stable oxygen isotope ratios, to reconstruct monthly river discharge at four key gauging stations that represent the four main tributaries of the Chao Phraya River, Thailand, thus bridging the gap between tree rings and water management. Our reconstructions, spanning 254 years (1750–2003), are the first monthly streamflow reconstructions outside North America, and the first ones that combine ring width and oxygen isotope data. Importantly, the reconstructions provide a detailed accounting of past droughts, pluvials, and wet season timings. This knowledge and data could be used to inform water management decisions, such as the operation of large reservoirs supplying hydropower and water for irrigation. This functional data set is a significant improvement over conventional annual reconstructions. Key Points Monthly‐resolved reconstructions of streamflow across the Chao Phraya River Basin are produced from ring widths and δ18O Droughts and pluvials across the Chao Phraya show both coherence and heterogeneity in time and space The reconstruction reveals the spatiotemporal variability of wet season timing