Streamflow drought identification and characterization in a tropical Andean basin: effect of threshold methods

Streamflow droughts in the Tropical Andes are poorly understood despite their increasing relevance due to climate change and rising water demand. This study compared fixed and variable threshold methods to identify streamflow droughts at a daily scale using four discharge stations in the Tomebamba River Basin, Ecuador. Results revealed substantial differences in drought characterization depending on the method. The variable threshold captured seasonal transitions by identifying events that extended across different seasons (on average, 25% of the events of each seasonal prolongation). In contrast, the fixed threshold detected low-flow events during the second dry period (65% of the events). Short-duration events (duration average at each station using variable threshold: 34, 29, 35 and 41 days) reflect the rapid hydrological response and suggest a small lag between meteorological and streamflow droughts. The findings provide a baseline for improving drought detection and advancing water management strategies in the Tropical Andes.