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.