  Where are the Earth's streams flowing right now? Inland surface waters expand
with floods and contract with droughts, so there is no one map of our streams.
Current satellite approaches are limited to monthly observations that map only
the widest streams. These are fed by smaller tributaries that make up much of
the dendritic surface network but whose flow is unobserved. A complete map of
our daily waters can give us an early warning for where droughts are born: the
receding tips of the flowing network. Mapping them over years can give us a map
of impermanence of our waters, showing where to expect water, and where not to.
To that end, we feed the latest high-res sensor data to multiple deep learning
models in order to map these flowing networks every day, stacking the times
series maps over many years. Specifically, i) we enhance water segmentation to
$50$ cm/pixel resolution, a 60$\times$ improvement over previous
state-of-the-art results. Our U-Net trained on 30-40cm WorldView3 images can
detect streams as narrow as 1-3m (30-60$\times$ over SOTA). Our multi-sensor,
multi-res variant, WasserNetz, fuses a multi-day window of 3m PlanetScope
imagery with 1m LiDAR data, to detect streams 5-7m wide. Both U-Nets produce a
water probability map at the pixel-level. ii) We integrate this water map over
a DEM-derived synthetic valley network map to produce a snapshot of flow at the
stream level. iii) We apply this pipeline, which we call Pix2Streams, to a
2-year daily PlanetScope time-series of three watersheds in the US to produce
the first high-fidelity dynamic map of stream flow frequency. The end result is
a new map that, if applied at the national scale, could fundamentally improve
how we manage our water resources around the world.
