Combined modelling of US fluvial, pluvial and coastal flood hazard under
current and future climates
Abstract
This paper reports a new and significantly enhanced analysis of US flood
hazard at 30m spatial resolution. Specific improvements include updated
hydrography data, new methods to determine channel depth, more rigorous
flood frequency analysis, output downscaling to property tract level and
inclusion of the impact of local interventions in the flooding system.
For the first time we consider pluvial, fluvial and coastal flood
hazards within the same framework and provide projections for both
current (rather than historic average) conditions and for future time
periods centred on 2035 and 2050 under the RCP4.5 emissions pathway.
Validation against high quality local models and the entire catalogue of
FEMA 1% annual probability flood maps yielded Critical Success Index
values in the range 0.69-0.82. Significant improvements over a previous
pluvial/fluvial model version are shown for high frequency events and
coastal zones, along with minor improvements in areas where model
performance was already good. The result is the first comprehensive and
consistent national scale analysis of flood hazard for the conterminous
US for both current and future conditions. Even though we consider a
stabilization emissions scenario and a near future time horizon we
project clear patterns of changing flood hazard (-3.8 to +16% changes
in 100yr inundated area at 1° scale), that are significant when
considered as a proportion of the land area where human use is possible
or in terms of the currently protected land area where the standard of
flood defence protection may become compromised by this time.