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

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.