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Abstract Compound floods are often thought of as large, infrequent floods during which extremes of coastal sea level and/or river flow combine with each other or additional factors (e.g., tides and rainfall) to induce major flooding. However, little is known about the potentially compound nature of more frequent, lower‐level floods. Here, we introduce the term “compound minor floods” to define minor floods composed of two or more water‐level sources. We use the Delaware River Estuary as a case study to investigate the prevalence and composition of these minor compound floods along the extent of a tidal river. We apply multiple linear regression to a 22‐year time series of coastal water levels and river discharge to establish the contributions of tides, nontidal open‐ocean effects, and river discharge to minor flood events at eight locations along the tidal Delaware River. We find that most minor flood events are compound in nature, requiring at least two components (e.g., tides and river discharge) to initiate flooding. We identify spatial structure in the relative importance of oceanographic and riverine contributions to minor flooding along the tidal reach of the estuary. These results suggest that incorporating fluvial components into minor flooding assessments is important to fully characterize flood risk along tidal rivers and estuaries. 

Abstract The Gulf Stream is a vital limb of the North Atlantic circulation that influences regional climate, sea level, and hurricane activity. Given the Gulf Stream's relevance to weather and climate, many studies have attempted to estimate trends in its volumetric transport from various data sets, but results have been inconclusive, and no consensus has emerged whether it is weakening with climate change. Here we use Bayesian analysis to jointly assimilate multiple observational data sets from the Florida Straits to quantify uncertainty and change in Gulf Stream volume transport since 1982. We find with virtual certainty (probabilityP > 99%) that Gulf Stream volume transport through the Florida Straits declined by 1.2 ± 1.0 Sv in the past 40 years (95% credible interval). This significant trend has emerged from the data set only over the past ten years, the first unequivocal evidence for a recent multidecadal decline in this climate‐relevant component of ocean circulation. 

Abstract Scientific and societal interest in the relationship between the Atlantic Meridional Overturning Circulation (AMOC) and U.S. East Coast sea level has intensified over the past decade, largely due to (1) projected, and potentially ongoing, enhancement of sea level rise associated with AMOC weakening and (2) the potential for observations of U.S. East Coast sea level to inform reconstructions of North Atlantic circulation and climate. These implications have inspired a wealth of model‐ and observation‐based analyses. Here, we review this research, finding consistent support in numerical models for an antiphase relationship between AMOC strength and dynamic sea level. However, simulations exhibit substantial along‐coast and intermodel differences in the amplitude of AMOC‐associated dynamic sea level variability. Observational analyses focusing on shorter (generally less than decadal) timescales show robust relationships between some components of the North Atlantic large‐scale circulation and coastal sea level variability, but the causal relationships between different observational metrics, AMOC, and sea level are often unclear. We highlight the importance of existing and future research seeking to understand relationships between AMOC and its component currents, the role of ageostrophic processes near the coast, and the interplay of local and remote forcing. Such research will help reconcile the results of different numerical simulations with each other and with observations, inform the physical origins of covariability, and reveal the sensitivity of scaling relationships to forcing, timescale, and model representation. This information will, in turn, provide a more complete characterization of uncertainty in relevant relationships, leading to more robust reconstructions and projections.