Despite having offered important hydroclimatic insights, streamflow
reconstructions still see limited use in water resources operations,
because annual reconstructions are not suitable for decisions at finer
time scales. Attempts towards sub-annual reconstructions have relied on
statistical disaggregation, which uses none or little proxy information.
Here, we develop a novel framework that optimizes proxy combinations to
simultaneously produce seasonal and annual reconstructions. Importantly,
the framework ensures that total seasonal flow matches annual flow
closely. This mass balance criterion is necessary to avoid misguiding
water management decisions, such as water allocation. Using the
framework, and leveraging a multi-species network of ring width and
cellulose δ18O in Southeast Asia, we reconstruct seasonal and annual
inflow to Thailand’s largest reservoir. The reconstructions are
statistically skillful. This work is one step closer towards operational
usability of streamflow reconstruction in water resources management.