Abstract
Global flood mapping has developed rapidly over the past decade, but
previous approaches have limited scope, function, and accuracy. These
limitations restrict the applicability and fundamental science questions
that can be answered with existing model frameworks. Harnessing recently
available data and modelling methods, this paper presents a new global
~30 m resolution Global Flood Map (GFM) with complete
coverage of fluvial, pluvial, and coastal perils, for any return period
or climate scenario, including accounting for uncertainty. With an
extensive compilation of global benchmark case studies – ranging from
locally collected event water levels, to national inventories of
engineering flood maps – we execute a comprehensive validation of the
new GFM. For flood extent comparisons, we demonstrate that the GFM
achieves a critical success index of ~0.75. In the more
discriminatory tests of flood water levels, the GFM deviates from
observations by ~0.6 m on average. Results indicating
this level of global model fidelity are unprecedented in the literature.
With an optimistic scenario of future warming (SSP1-2.6), we show
end-of-century global flood hazard increases are limited to 9% (likely
range -6–29%); this is within the likely climatological uncertainty of
-8–12% in the current hazard estimate. In contrast, pessimistic
scenario (SSP5-8.5) hazard changes emerge from the background noise in
the 2040s, rising to a 49% (likely range of 7–109%) increase by 2100.
This work verifies the fitness-for-purpose of this new-generation GFM
for impact analyses with a variety of beneficial applications across
policymaking, planning, and commercial risk assessment.