Given the geomorphology of the two continents, it is unsurprising
that there are differences in the observability of freshwater ecosystems.
Europe was recently glaciated and has many areas of sharp relief,resulting in runoff and drainage patterns that lead tomore spatially simple
and pseudo-symmetrical polygons. Australia, on the other hand,was
largely unglaciated, has much lower relief and exceptionally long
hydrologic residence times, resulting in sinuous, spatially complex systems
not amenable to observations using large pixels. These estimates
of detectable freshwater ecosystems are predicated on the assumption
that the base vector datasets are accurate and comparable, which is
not entirely met. For example, the base vector layers are of different
mapping scales, though on the same order ofmagnitude.Whilewe consider
our estimates to be conservative based on the 4 × 4 pixel requirement,
they could also potentially be overestimates if the vector layers do
not represent small or isolatedwater bodies andwetlands. However,we
can conclude that the suitability of HyspIRI's proposed spatial resolution
of 60 m for global freshwater ecosystem measurements will vary geographically
based on both the geomorphology of each continent,
which will control the size and shape of the freshwater systems.