Abstract. The interaction between physical drivers from
oceanographic, hydrological, and meteorological processes in coastal areas
can result in compound flooding. Compound flood events, like Cyclone Idai
and Hurricane Harvey, have revealed the devastating consequences of the
co-occurrence of coastal and river floods. A number of studies have recently
investigated the likelihood of compound flooding at the continental scale
based on simulated variables of flood drivers, such as storm surge,
precipitation, and river discharges. At the global scale, this has only been
performed based on observations, thereby excluding a large extent of the
global coastline. The purpose of this study is to fill this gap and identify
regions with a high compound flooding potential from river discharge and
storm surge extremes in river mouths globally. To do so, we use daily
time series of river discharge and storm surge from state-of-the-art global
models driven with consistent meteorological forcing from reanalysis
datasets. We measure the compound flood potential by analysing both
variables with respect to their timing, joint statistical dependence, and
joint return period. Our analysis indicates many regions that deviate from
statistical independence and could not be identified in previous global
studies based on observations alone, such as Madagascar, northern Morocco,
Vietnam, and Taiwan. We report possible causal mechanisms for the observed
spatial patterns based on existing literature. Finally, we provide
preliminary insights on the implications of the bivariate dependence
behaviour on the flood hazard characterisation using Madagascar as a case
study. Our global and local analyses show that the dependence structure
between flood drivers can be complex and can significantly impact the joint
probability of discharge and storm surge extremes. These emphasise the need
to refine global flood risk assessments and emergency planning to account
for these potential interactions.
Measuring compound flood potential from river discharge and storm surge extremes at the global scale
