Revisiting Michael Bonell's work on humid tropical rainforest catchments: Isotope tracers reveal seasonal shifts in catchment hydrology

It has been almost 50 years since the foundational work at Babinda catchments in North Queensland kickstarted field of tropical hydrology globally. To expand upon this and build a more generalized hydrological understanding steep rainforest catchments, we studied seasonal evolution response from two with broadly similar characteristics to catchments. Both hydrometric water stable isotope data were collected relatively high frequencies during one wet season (Thompson Creek) 3-year period (Atika Creek). The longer dataset spans wide range environmental conditions experienced humid tropics, including events that cover wetting-up transitional cyclones (TC). displayed fast streamflow rainfall shallow upper soil profile responding quickly Atika Creek. New findings study include importance pre-event (>50% using component hydrograph separation technique) for overall event flows, especially when catchment was wet. Rainfall, surface runoff groundwater specific electrical conductivity (SEC) compositions varied between most complex bivariate mixing plots observed multi-peak occurred start after dry within season. Two-tracer, 3 separations did not provide satisfactory results identifying source contributions streamflow. These highlighted time-variant non-conservative behaviour rainfall, waters over timescale, being an important unidentified contributor. Our highlight need frequency multi-source sampling accurately interpret We propose framework describe experiencing activity.