More Like this

1. Co-evolution of wetland landscapes, flooding, and human settlement in the Mississippi River Delta Plain

   https://doi.org/10.1007/s11625-016-0374-4  

   Twilley, Robert R.; Bentley, Samuel J.; Chen, Qin; Edmonds, Douglas A.; Hagen, Scott C.; Lam, Nina S.-N.; Willson, Clinton S.; Xu, Kehui; Braud, DeWitt; Hampton Peele, R.; et al (May 2016, Sustainability Science)

   Abstract River deltas all over the world are sinking beneath sea-level rise, causing significant threats to natural and social systems. This is due to the combined effects of anthropogenic changes to sediment supply and river flow, subsidence, and sea-level rise, posing an immediate threat to the 500–1,000 million residents, many in megacities that live on deltaic coasts. The Mississippi River Deltaic Plain (MRDP) provides examples for many of the functions and feedbacks, regarding how human river management has impacted source-sink processes in coastal deltaic basins, resulting in human settlements more at risk to coastal storms. The survival of human settlement on the MRDP is arguably coupled to a shifting mass balance between a deltaic landscape occupied by either land built by the Mississippi River or water occupied by the Gulf of Mexico. We developed an approach to compare 50 % L:W isopleths (L:W is ratio of land to water) across the Atchafalaya and Terrebonne Basins to test landscape behavior over the last six decades to measure delta instability in coastal deltaic basins as a function of reduced sediment supply from river flooding. The Atchafalaya Basin, with continued sediment delivery, compared to Terrebonne Basin, with reduced river inputs, allow us to test assumptions of how coastal deltaic basins respond to river management over the last 75 years by analyzing landward migration rate of 50 % L:W isopleths between 1932 and 2010. The average landward migration for Terrebonne Basin was nearly 17,000 m (17 km) compared to only 22 m in Atchafalaya Basin over the last 78 years (p\0.001), resulting in migration rates of 218 m/year (0.22 km/year) and\0.5 m/year, respectively. In addition, freshwater vegetation expanded in Atchafalaya Basin since 1949 compared to migration of intermediate and brackish marshes landward in the Terrebonne Basin. Changes in salt marsh vegetation patterns were very distinct in these two basins with gain of 25 % in the Terrebonne Basin compared to 90 % decrease in the Atchafalaya Basin since 1949. These shifts in vegetation types as L:W ratio decreases with reduced sediment input and increase in salinity also coincide with an increase in wind fetch in Terrebonne Bay. In the upper Terrebonne Bay, where the largest landward migration of the 50 % L:W ratio isopleth occurred, we estimate that the wave power has increased by 50–100 % from 1932 to 2010, as the bathymetric and topographic conditions changed, and increase in maximum storm-surge height also increased owing to the landward migration of the L:W ratio isopleth. We argue that this balance of land relative to water in this delta provides a much clearer understanding of increased flood risk from tropical cyclones rather than just estimates of areal land loss. We describe how coastal deltaic basins of the MRDP can be used as experimental landscapes to provide insights into how varying degrees of sediment delivery to coastal deltaic floodplains change flooding risks of a sinking delta using landward migrations of 50 % L:W isopleths. The nonlinear response of migrating L:W isopleths as wind fetch increases is a critical feedback effect that should influence human river-management decisions in deltaic coast. Changes in land area alone do not capture how corresponding landscape degradation and increased water area can lead to exponential increase in flood risk to human populations in low-lying coastal regions. Reduced land formation in coastal deltaic basins (measured by changes in the land:water ratio) can contribute significantly to increasing flood risks by removing the negative feedback of wetlands on wave and storm-surge that occur during extreme weather events. Increased flood risks will promote population migration as human risks associated with living in a deltaic landscape increase, as land is submerged and coastal inundation threats rise. These system linkages in dynamic deltaic coasts define a balance of river management and human settlement dependent on a certain level of land area within coastal deltaic basins (L). 

   more » « less
2. Breaking down annual and tropical cyclone-induced nonlinear interactions in total water levels

   Sakib, M S; Muñoz, D F; Wahl, T (December 2025, Advances in water resources)

   With the increase of tropical cyclone activity, coastal communities will experience growing impacts from extreme water levels and associated compound flooding. Multiple drivers contribute to total water level (TWL), including mean sea level, astronomical tides, riverine flow, storm surges, and waves. Therefore, gaining insight into future TWL variability requires a thorough understanding of how those drivers nonlinearly interact at different spatiotemporal scales. In this study, we developed a coupled coastal and wave model at sufficient spatial resolution to analyze: (i) tide–driver interactions and their nonlinear components stemming from surge, river flow, and wind-waves, and (ii) their spatiotemporal evolution across the pre-landfall, landfall, and post-landfall stages of tropical cyclones in the Chesapeake Bay, USA. Results show that tide–surge and tide–wave interactions, along with their nonlinear components, exhibit substantial annual variability, with extreme hurricanes producing abrupt and spatially distinct responses driven by low pressure anomalies in slow-moving storms and wind setup in faster systems. In contrast, tide–river interactions remain negligible except in the upper bay tributaries. A weak or neutral tide–driver interaction does not necessarily indicate a negligible nonlinear response. Rather, nonlinear interactions (NIs) generally act out of phase with their associated drivers, functioning as compensatory mechanisms that amplify or suppress TWL. These nonlinearities are transient and of high-frequency nature near the coast, but evolve into slower, more persistent fluctuations in upstream regions. As climate change reshapes coastal dynamics, a robust understanding of NIs is essential for designing effective flood protection, enhancing risk assessments, and developing informed adaptation strategies for extreme water levels. 

   more » « less
3. First‐Order River Delta Morphology Is Explained by the Sediment Flux Balance From Rivers, Waves, and Tides

   https://doi.org/10.1029/2022GL100355  

   Broaddus, C. M.; Vulis, L. M.; Nienhuis, J. H.; Tejedor, A.; Brown, J.; Foufoula‐Georgiou, E.; Edmonds, D. A. (November 2022, Geophysical Research Letters)

   Abstract We present a novel quantitative test of a 50‐year‐old hypothesis which asserts that river delta morphology is determined by the balance between river and marine influence. We define three metrics to capture the first‐order morphology of deltas (shoreline roughness, number of distributary channel mouths, and presence/absence of spits), and use a recently developed sediment flux framework to quantify the river‐marine influence. Through analysis of simulated and field deltas we quantitatively demonstrate the relationship between sediment flux balance and delta morphology and show that the flux balance accounts for at least 35% of the variance in the number of distributary channel mouths and 42% of the variance in the shoreline roughness for real‐world and simulated deltas. We identify a tipping point in the flux balance where wave influence halts distributary channel formation and show how this explains morphological transitions in real world deltas. 

   more » « less
4. Global rates and patterns of channel migration in river deltas

   https://doi.org/10.1073/pnas.2103178118  

   Jarriel, Teresa; Swartz, John; Passalacqua, Paola (November 2021, Proceedings of the National Academy of Sciences)

   River deltas are dynamic systems whose channels can widen, narrow, migrate, avulse, and bifurcate to form new channel networks through time. With hundreds of millions of people living on these globally ubiquitous systems, it is critically important to understand and predict how delta channel networks will evolve over time. Although much work has been done to understand drivers of channel migration on the individual channel scale, a global-scale analysis of the current state of delta morphological change has not been attempted. In this study, we present a methodology for the automatic extraction of channel migration vectors from remotely sensed imagery by combining deep learning and principles from particle image velocimetry (PIV). This methodology is implemented on 48 river delta systems to create a global dataset of decadal-scale delta channel migration. By comparing delta channel migration distributions with a variety of known external forcings, we find that global patterns of channel migration can largely be reconciled with the level of fluvial forcing acting on the delta, sediment flux magnitude, and frequency of flood events. An understanding of modern rates and patterns of channel migration in river deltas is critical for successfully predicting future changes to delta systems and for informing decision makers striving for deltaic resilience. 

   more » « less
5. Influence of storm type on compound flood drivers of a mid-latitude coastal urban environment

   https://doi.org/10.5194/hess-29-3101-2025  

   Chen, Ziyu; Orton, Philip M; Booth, James F; Wahl, Thomas; DeGaetano, Arthur; Kaatz, Joel; Horton, Radley M (July 2025, Hydrology and Earth System Sciences)

   A common feature within coastal cities is small, urbanized watersheds where the time of concentration is short, leading to vulnerability to flash flooding during coastal storms that can also cause storm surge. While many recent studies have provided evidence of dependency in these two flood drivers for many coastal areas worldwide, few studies have investigated their co-occurrence locally in detail or the storm types that are involved. Here we present a bivariate statistical analysis framework with historical rainfall and storm surge and tropical cyclone (TC) and extratropical cyclone (ETC) track data, using New York City (NYC) as a mid-latitude demonstration site where these storm types play different roles. In contrast to prior studies that focused on daily or longer durations of rain, we apply hourly data and study simultaneous drivers and lags between them. We quantify characteristics of compound flood drivers, including their dependency, magnitude, lag time, and joint return periods (JRPs), separately for TCs, ETCs, non-cyclone-associated events, and merged data from all events. We find TCs have markedly different driver characteristics from other storm types and dominate the joint probabilities of the most extreme rain surge compound events, even though they occur much less frequently. ETCs are the predominant source of more frequent moderate compound events. The hourly data also reveal subtle but important spatial differences in lag times between the joint flood drivers. For Manhattan and southern shores of NYC during top-ranked TC rain events, rain intensity has a strong negative correlation with lag time to peak surge, promoting pluvial–coastal compound flooding. However, for the Bronx River in northern NYC, fluvial–coastal compounding is favored due to a 2–6 h lag from the time of peak rain to peak surge. 

   more » « less