Recent streamflow variability linked to climate, dam operations and land cover change in the Irrawaddy River, Southeast Asia

Irrawaddy River, Myanmar, Southeast Asia Detection of streamflow changes serves as a critical foundation for water resources management. The data-scarce Irrawaddy is ideally positioned for this study, as investigations of regional hydrology are lacking, despite being one of the largest rivers in Southeast Asia. Hence, this work achieves an unprecedented and detailed analysis of the Irrawaddy streamflow variability from 2001 to 2023 due to climate, dams, and land cover change. The assessment integrated trend analyses with diagnostic modeling using the Variable Infiltration Capacity with reservoir module (VIC-Res) for two sets of scenarios: a set with and without dam operations, and another without dams using fixed 2001 and 2023 land cover. Streamflow significantly decreased in the lower Irrawaddy. Moreover, the Irrawaddy streamflow variability was mainly attributed to climate for two proven reasons. First, both land cover change and dam operations contributed marginally to mean seasonal and annual streamflow changes (around ±2 %) due to small land cover change basin-wide (within ±5 %) and that all dams are on low-order tributaries with the degree of regulation of only 2 %. Compared to the effect of land cover change on streamflow, dams exerted higher flow changes in magnitude and variability. Second, precipitation and streamflow maintained a statistically significant linear correlation ( p < 0.01) and exhibited similar decreasing tendency, despite no significance detected for precipitation. This study enhances understanding of the Irrawaddy’s contemporary hydrology to support basin-scale water resources management. • Significant declines in dry-season and annual flows were detected near the outlet. • Precipitation exhibited similar tendency and significant correlation with flows. • Dams exist on low-order tributaries; basin-wide land cover change was modest. • Dams and land cover change impacts were assessed through scenario modeling. • Departures from natural flows were marginal, with dams exerting higher impacts.