Global hydroclimatic controls on multithread river dynamics

Most large rivers in densely populated areas split flow into multiple channels, forming interconnected pathways called threads. Multithread rivers are sensitive to hydroclimatic changes, yet understanding their dynamics is challenging due to the lack of robust metrics to characterize their evolution. To investigate the drivers of river evolution, we analyze 38 years of Landsat imagery alongside discharge records for 97 multithread  reaches worldwide spanning diverse climates and both wandering and braided morphologies. We quantify the number of active threads and their allocated discharge through space and time using the entropic Braiding Index (eBI), coupled with metrics for bank migration rate, floodplain reworking, and channel-belt size. Data reveal that multithread river dynamics are strongly controlled by flow intermittency—expressed as the dimensionless ratio of long-term mean discharge to bankfull discharge. Rivers with lower flow intermittency (i.e., higher discharge relative to bankfull conditions) exhibit more active threads, decelerated thread migration, prolonged floodplain reworking timescales, and smaller channel-belt area normalized by channelized area. Lower flow intermittency also results in preferential flow routing among threads (lower eBI relative to thread count). Channel-belt area relative to channelized area exponentially declines with thread count, potentially reflecting a greater propensity for reconfiguration over lateral migration in braided rivers. Furthermore, multithread rivers in cold climates exhibit slower evolution rates across scales, likely due to permafrost influence. Together, results suggest that future increases in discharge variability could cause multithread rivers to split into more active threads and accelerate movement within channel belts, potentially impacting livelihoods and ecosystems along river corridors.