Coastal River Deltas Research Articles

Mangroves as nature-based mitigation for ENSO-driven compound flood risks in a large river delta

Abstract. Densely populated coastal river deltas are very vulnerable to compound flood risks coming from both oceanic and riverine sources. Climate change may increase these compound flood risks due to sea level rise and intensifying precipitation events. Here, we investigate to what extent nature-based flood defence strategies, through the conservation of mangroves in a tropical river delta, can contribute to mitigate the oceanic and riverine components of compound flood risks. While current knowledge of estuarine compound flood risks is mostly focussed on short-term events such as storm surges (taking 1 or a few days), longer-term events, such as El Niño events (continuing for several weeks to months) along the Pacific coast of Latin America, are less studied. Here, we present a hydrodynamic modelling study of a large river delta in Ecuador aiming to elucidate the compound effects of El Niño-driven oceanic and riverine forcing on extreme high water level propagation through the delta and, in particular, the role of mangroves in reducing the compound high water levels. Our results show that the deltaic high water level anomalies are predominantly driven by the oceanic forcing but that the riverine forcing causes the anomalies to amplify upstream. Furthermore, mangroves in the delta attenuate part of the oceanic contribution to the high water level anomalies, with the attenuating effect increasing in the landward direction, while mangroves have a negligible effect on the riverine component. These findings show that mangrove conservation and restoration programmes can contribute to nature-based mitigation, especially the oceanic component of compound flood risks in a tropical river delta.

Short-Term Sediment Dispersal on a Large Retreating Coastal River Delta via 234Th and 7Be Sediment Geochronology: The Mississippi River Delta Front

Many Mississippi River Delta studies have shown recent declines in fluvial sediment load from the river and associated land loss. In contrast, recent sedimentary processes on the subaqueous delta are less documented. To help address this knowledge gap, multicores were collected offshore from the three main river outlets at water depths of 25–280 m in June 2017 just after the peak river discharge period, with locations selected based on 2017 U.S. Geological Survey seabed mapping. The coring locations included the undisturbed upper foreset, mudflow lobes, gullies, and the undisturbed prodelta. Nine multicores were analyzed for Beryllium-7 activity, and four cores were analyzed for excess Thorium-234 activity via gamma spectrometry, granulometry and X-radiography. Our results indicate a general trend of declining 7Be and 234Th activities and inventories with increasing distance from sources and in deeper water. The core X-radiographs are graded from the predominantly physically stratified nearshore to the more bioturbated offshore, consistent with the sedimentation patterns. Sediment focusing assessed via the 7Be and 234Th sediment inventories shows preferential sedimentation in gully and lobe environments, whereas the upper foreset and prodelta focusing factors are relatively depleted. Overall, short-term sediment deposition from the main fluvial source remains active offshore from all three major river outlets, despite the overall declining river load.

Incorporating ecosystem services into comparative vulnerability and risk assessments in the Pearl River and Yangtze River Deltas, China

Coastal river deltas face high risks from multiple natural hazards due to the combined effects of human activities, natural processes, and climate change. Vulnerability and risk assessments are essential for reducing and managing risks and, in the process, contribute to sustainable development. Despite adopting a social-ecological and multi-hazard perspective, previous risk assessments failed to achieve balanced consideration of both social and ecological sub-systems. To address this gap, we used an integrated risk assessment framework which incorporates the role of ecosystem services (ES) as a core component. A modular indicator library of ES indicators relevant to coastal river deltas was used to characterize multi-risks in the Pearl and Yangtze River deltas. Results indicate a higher risk level in the Pearl River Delta, with the key drivers of vulnerability and risk varying with scales. Visualizing hazard-prone and highly vulnerable areas facilitates the implementation of targeted management measures and policies to reduce disaster risks from natural hazards. Ecosystem services have been identified as important factors of the risk profiles, and their inclusion in risk reduction strategies ensures that policies can be put in place that allow ecosystems to provide services sustainably to communities.

Quantifying the factors controlling groundwater fluoride and associated health risks in the coastal river delta, northern China

Chronic exposure to high fluoride (F-) groundwater has a detrimental effect on the health of hundreds of millions of individuals worldwide. High F- groundwater in coastal areas is frequently observed, but the extent to which various factors influence the distribution of F- concentrations and the health hazards posed to different populations by consuming this groundwater have not been widely documented. In this study, 207 groundwater samples were acquired from the shallow and deep aquifers in the Luanhe River Delta, with an aim to investigate controlling factors and health hazards associated with groundwater F-. In the shallow aquifers, high F- groundwater was mainly determined by mineral dissolution and precipitation, desorption and competitive adsorption, and cation exchange, with relative contributions of 93.6%, 3.8%, and 2.2% respectively. The evaporation and seawater intrusion had little influence on groundwater F- enrichment. With respective contributions of 55.9%, 32.4%, 9.2%, and 2.5%, mineral dissolution and precipitation, desorption and competitive adsorption, geothermal waters, and cation exchange jointly regulated the distribution of groundwater F- in the deep aquifers. The health risk assessments showed that shallow groundwater F- through oral intake and dermal contact posed health hazards to 61.1% of infants, 38.9% of children, 26.7% of adult females and 31.1% of adult males, while in deep groundwater, these percentages were 66.4%, 32.8%, 22.1% and 28.7%, respectively. The present study provides a significant contribution towards enhancing the comprehension of the evolution of groundwater F- in coastal regions, and thereby, establishes a sound scientific basis for the effective management of drinking water.

The effect of the local environment on child nutritional outcomes: how does seasonality relate to wasting amongst children under 5 in south-west coastal Bangladesh?

The impact of short-term environmental changes on child nutritional status is not constant within populations. In many countries, the seasons are closely linked with many factors that are known to affect nutritional outcomes, such as food consumption, crop harvests, employment opportunities and illness. With extreme seasonal variation becoming more common, understanding how seasonality is related to child nutritional outcomes is vital. This study will explore spatial and temporal variation and determinants for acute malnutrition in a coastal river delta in south-west Bangladesh over the period of a year. Using a rural longitudinal survey, conducted in 2014–15 with 3 survey waves, wasting amongst children under 5 was studied. Spatial variation was analysed through ‘socio-ecological systems’, which capture interactions between ecosystems, livelihoods and populations. Wasting prevalence varied from 18.2% in the monsoon season to 8.7% post-major rice harvest (Aman). Seasons did not relate to wasting consistently over socio-ecological systems, with some systems showing greater variability over time, highlighting distinct seasonal dynamics in nutritional status. Wealthier socio-ecological systems had lower wasting generally, as expected, with greater livelihood diversification opportunities and strategies to smooth consumption. Nutrition interventions must consider seasonal peaks in acute malnutrition, as well as the environmental context when implementing programmes to maximise effectiveness. With increasing variability in seasonal changes, inequalities in the impact of season must be accounted for in health promotion activities. Furthermore, timing and season of survey implementation is an important factor to be accounted for in nutrition research, especially when comparing between two cross-sectional surveys.

Global change scenarios in coastal river deltas and their sustainable development implications

Deltas play a critical role in the ambition to achieve global sustainable development given their relatively large shares in population and productive croplands, as well as their precarious low-lying position between upstream river basin development and rising seas. The large pressures on these systems risk undermining the persistence of delta societies, economies, and ecosystems. We analyse possible future development in 49 deltas around the globe under the Shared Socio-economic and Representative Concentration Pathways until 2100. Population density, urban fraction, and total and irrigated cropland fraction are three to twelve times greater in these deltas, on average, than in the rest of the world. Maximum river water discharges are projected to increase by 11–33 % and river sediment discharges are projected to decrease 26–37 % on average, depending on the scenario. Regional sea-level rise reaches almost 1.0 m by 2100 for certain deltas in the worst-case scenario, increasing to almost 2.0 m of relative rise considering land subsidence. Extreme sea levels could be much higher still—reaching over 4.0 m by 2100 for six of the 49 deltas analysed. Socio-economic conditions to support adaptation are the weakest among deltas with the greatest pressures, compounding the challenge of sustainable development. Asian and African deltas stand out as having heightened socio-economic challenges—huge population and land use pressures in most Asian deltas and the Nile delta; low capacity for adaptation in most African deltas and the Irrawaddy delta. Although, deltas in other parts of the world are not immune from these and other pressures, either. Because of unique pressures and processes operating in deltas, as in other “hotspots” such as small islands, mountains, and semi-arid areas, we recommend greater consideration and conceptualisation of environmental processes in global sustainable development agendas and in the Integrated Assessment Models used to guide global policy.

Agricultural Water Quality Assessment and Application in the Yellow River Delta

Irrigation is the primary agricultural utilization of water resources worldwide, and it produces 36% of the food. The quality of irrigation water influences crop growth and food safety. The coastal river delta region supplies huge area lands for developing agriculture, and the irrigation in this area is composed of many resources for its special location. This study investigated the agricultural water with different resources and evaluated its quality in the Yellow River Delta. The water samples included irrigation water, underground water, and drainage water. The sampling points were designed in the typical areas of Kenli county and Guangrao county in Dongying city, which is the core area of the Yellow River Delta. Through testing the ions composition and the parameters of electrical conductivity (EC), pH, and so on, six evaluation methods were conducted to assess the water quality. The results suggested that the Yellow River water has good quality for irrigation or unconventional water utilization. The high concentration of Na+ and Cl− was the primary problem of the water resource. The rainfall was also another water resource supplement in this region. Therefore, developing saline water irrigation incorporated with salt-tolerant crop cultivation is a rational measure for improving coastal agriculture in the Yellow River Delta.

A globally applicable framework for compound flood hazard modeling

Abstract. Coastal river deltas are susceptible to flooding from pluvial, fluvial, and coastal flood drivers. Compound floods, which result from the co-occurrence of two or more of these drivers, typically exacerbate impacts compared to floods from a single driver. While several global flood models have been developed, these do not account for compound flooding. Local-scale compound flood models provide state-of-the-art analyses but are hard to scale to other regions as these typically are based on local datasets. Hence, there is a need for globally applicable compound flood hazard modeling. We develop, validate, and apply a framework for compound flood hazard modeling that accounts for interactions between all drivers. It consists of the high-resolution 2D hydrodynamic Super-Fast INundation of CoastS (SFINCS) model, which is automatically set up from global datasets and coupled with a global hydrodynamic river routing model and a global surge and tide model. To test the framework, we simulate two historical compound flood events, Tropical Cyclone Idai and Tropical Cyclone Eloise in the Sofala province of Mozambique, and compare the simulated flood extents to satellite-derived extents on multiple days for both events. Compared to the global CaMa-Flood model, the globally applicable model generally performs better in terms of the critical success index (−0.01–0.09) and hit rate (0.11–0.22) but worse in terms of the false-alarm ratio (0.04–0.14). Furthermore, the simulated flood depth maps are more realistic due to better floodplain connectivity and provide a more comprehensive picture as direct coastal flooding and pluvial flooding are simulated. Using the new framework, we determine the dominant flood drivers and transition zones between flood drivers. These vary significantly between both events because of differences in the magnitude of and time lag between the flood drivers. We argue that a wide range of plausible events should be investigated to obtain a robust understanding of compound flood interactions, which is important to understand for flood adaptation, preparedness, and response. As the model setup and coupling is automated, reproducible, and globally applicable, the presented framework is a promising step forward towards large-scale compound flood hazard modeling.

Integrating Connectivity Into Hydrodynamic Models: An Automated Open‐Source Method to Refine an Unstructured Mesh Using Remote Sensing

AbstractHydrodynamic models are an essential tool for studying the movement of water and other materials across the Earth surface. However, models remain limited by practical constraints on size and resolution, particularly in coastal environments containing topologically complex and multi‐scale channel/wetland networks. Unstructured meshes have helped address this problem by allowing resolution to vary spatially, and many models support local mesh refinement using breaklines or internal regions‐of‐interest. However, there remains no standardized, objective, or easily reproducible method to implement internal features between different users. The present study aims to address whether remote sensing can fill in that gap, by embedding information about landscape structure and connectivity directly into model meshes. We present an automated image processing methodology for preserving dynamically active connected features in the unstructured shallow‐water model ANUGA, while reducing computational demand in less active areas of the domain. The Unstructured Mesh Refinement Method (UMRM) converts a binary input raster into a collection of closed, simple polygons which can be used to refine the mesh, meanwhile preserving connectivity and enforcing model‐related constraints. We apply this workflow to a large‐scale model of two coastal river deltas, and refine our mesh using time‐series of optical Planet imagery, InSAR measurements of water level change, and topographic data. We compare the results of the connectivity‐preserving mesh to results from a mesh using a uniform mesh resolution, and find that the UMRM decreased the computational demand by a third, without any discernible loss in accuracy when compared to in‐situ and remotely sensed water level measurements.

Mapping Flood Extent and Frequency from Sentinel-1 Imagery during the Extremely Warm Winter of 2020 in Boreal Floodplains and Forests

The current study presents a methodology for water mapping from Sentinel-1 (S1) data and a flood extent analysis of the three largest floodplains in Estonia. The automatic processing scheme of S1 data was set up for the mapping of open-water flooding (OWF) and flooding under vegetation (FUV). The extremely mild winter of 2019/2020 resulted in several large floods at floodplains that were detected from S1 imagery with a maximal OWF extent up to 5000 ha and maximal FUV extent up to 4500 ha. A significant correlation (r2 > 0.6) between the OWF extent and the closest gauge data was obtained for inland riverbank floodplains. The outcome enabled us to define the water level at which the water exceeds the shoreline and flooding starts. However, for a coastal river delta floodplain, a lower correlation (r2 < 0.34) with gauge data was obtained, and the excess of river coastline could not be related to a certain water level. At inland riverbank floodplains, the extent of FUV was three times larger compared to that of OWF. The correlation between the water level and FUV was <0.51, indicating that the river water level at these test sites can be used as a proxy for forest floods. Relating conventional gauge data to S1 time series data contributes to flood risk mitigation.

Evaluating the Effectiveness of Climate Change Adaptations in the World’s Largest Mangrove Ecosystem

The Sundarbans is the world’s largest coastal river delta and the largest uninterrupted mangrove ecosystem. A complex socio-ecological setting, coupled with disproportionately high climate-change exposure and severe ecological and social vulnerabilities, has turned it into a climate hotspot requiring well-designed adaptation interventions. We have used the fuzzy cognitive maps (FCM)-based approach to elicit and integrate stakeholders’ perceptions regarding current climate forcing, consequent impacts, and efficacy of the existing adaptation measures. We have also undertaken climate modelling to ascertain long-term future trends of climate forcing. FCM-based simulations reveal that while existing adaptation practices provide resilience to an extent, they are grossly inadequate in the context of providing future resilience. Even well-planned adaptations may not be entirely transformative in such a fragile ecosystem. It was through FCM-based simulations that we realised that a coastal river delta in a developing nation merits special attention for climate-resilient adaptation planning and execution. Measures that are likely to enhance adaptive capabilities of the local communities include those involving gender-responsive and adaptive governance, human resource capacity building, commitments of global communities for adaptation financing, education and awareness programmes, and embedding indigenous and local knowledge into decision making.

Differences in long-term vs short-term carbon and nitrogen sequestration in a coastal river delta wetland: Implications for global budgets

Coastal wetlands can serve as a considerable sink for carbon (C) gases. However, the capacity for wetlands to serve as more permanent C and N sinks over the long term is less clear given the time dependence of sediment deposition, organic matter decomposition, and anthropogenic land use change. In this study, we compare the short-term (decadal scale) and long-term (millennial scale) C and N accumulation rates estimated using 137Cs and radiocarbon dating of vibracores collected from a freshwater coastal wetland in the Louisiana Mississippi River deltaic plain (Atchafalaya River delta). The mean short-term (60 yrs) sediment accumulation rate was 1.4 cm/yr while the mean rate of long-term (100–1000 yrs) sediment accumulation was an order of magnitude lower at 0.12 cm/yr. Annual rates of C and N accumulated over the past several thousand years were approximately 10% of that over the past 60 years after correcting for bulk density. These results are similar to other coastal wetlands and suggest that time scale must be considered in determining the relative permanence of C and N storage in coastal wetland soils. This difference is especially important for assessing the role of C cycling in relation to global change models and N cycling related to water quality in accurately quantifying the role of coastal deltaic fresh water wetlands in regulating these biogeochemical cycles.

Vulnerability and risk of deltaic social-ecological systems exposed to multiple hazards

Coastal river deltas are hotspots of global change impacts. Sustainable delta futures are increasingly threatened due to rising hazard exposure combined with high vulnerabilities of deltaic social-ecological systems. While the need for integrated multi-hazard approaches has been clearly articulated, studies on vulnerability and risk in deltas either focus on local case studies or single hazards and do not apply a social-ecological systems perspective. As a result, vulnerabilities and risks in areas with strong social and ecological coupling, such as coastal deltas, are not fully understood and the identification of risk reduction and adaptation strategies are often based on incomplete assumptions. To overcome these limitations, we propose an innovative modular indicator library-based approach for the assessment of multi-hazard risk of social-ecological systems across and within coastal deltas globally, and apply it to the Amazon, Ganges-Brahmaputra-Meghna (GBM), and Mekong deltas. Results show that multi-hazard risk is highest in the GBM delta and lowest in the Amazon delta. The analysis reveals major differences between social and environmental vulnerability across the three deltas, notably in the Mekong and the GBM deltas where environmental vulnerability is significantly higher than social vulnerability. Hotspots and drivers of risk vary spatially, thus calling for spatially targeted risk reduction and adaptation strategies within the deltas. Ecosystems have been identified as both an important element at risk as well as an entry point for risk reduction and adaptation strategies.

Channel‐Island Connectivity Affects Water Exposure Time Distributions in a Coastal River Delta

AbstractThe exposure time is a water transport time scale defined as the cumulative amount of time a water parcel spends in the domain of interest regardless of the number of excursions from the domain. Transport time scales are often used to characterize the nutrient removal potential of aquatic systems, but exposure time distribution estimates are scarce for deltaic systems. Here we analyze the controls on exposure time distributions using a hydrodynamic model in two domains: the Wax Lake delta in Louisiana, USA, and an idealized channel‐island complex. In particular, we study the effects of river discharge, vegetation, network geometry, and tides and use a simple model for the fractional removal of nitrate. In both domains, we find that channel‐island hydrological connectivity significantly affects exposure time distributions and nitrate removal. The relative contributions of the island and channel portions of the delta to the overall exposure time distribution are controlled by island vegetation roughness and network geometry. Tides have a limited effect on the system's exposure time distribution but can introduce significant spatial variability in local exposure times. The median exposure time for the WLD model is 10 h under the conditions tested and water transport within the islands contributes to 37–50% of the network‐scale exposure time distribution and 52–73% of the modeled nitrate removal, indicating that islands may account for the majority of nitrate removal in river deltas.

Pyroclastic Eruption Boosts Organic Carbon Fluxes Into Patagonian Fjords

AbstractFjords and old‐growth forests store large amounts of organic carbon. Yet the role of episodic disturbances, particularly volcanic eruptions, in mobilizing organic carbon in fjord landscapes covered by temperate rainforests remains poorly quantified. To this end, we estimated how much wood and soils were flushed to nearby fjords following the 2008 eruption of Chaitén volcano in south‐central Chile, where pyroclastic sediments covered >12 km2 of pristine temperate rainforest. Field‐based surveys of forest biomass, soil organic content, and dead wood transport reveal that the reworking of pyroclastic sediments delivered ~66,500 + 14,600/−14,500 tC of large wood to two rivers entering the nearby Patagonian fjords in less than a decade. A similar volume of wood remains in dead tree stands and buried beneath pyroclastic deposits (~79,900 + 21,100/−16,900 tC) or stored in active river channels (5,900–10,600 tC). We estimate that bank erosion mobilized ~132,300+21,700/−30,600 tC of floodplain forest soil. Eroded and reworked forest soils have been accreting on coastal river deltas at >5 mm yr−1 since the eruption. While much of the large wood is transported out of the fjord by long‐shore drift, the finer fraction from eroded forest soils is likely to be buried in the fjords. We conclude that the organic carbon fluxes boosted by rivers adjusting to high pyroclastic sediment loads may remain elevated for up to a decade and that Patagonian temperate rainforests disturbed by excessive loads of pyroclastic debris can be episodic short‐lived carbon sources.

Erratum for “What Controls the Transition from Confined to Unconfined Flow? Analysis of Hydraulics in a Coastal River Delta” by Matthew Hiatt and Paola Passalacqua

Erratum for “What Controls the Transition from Confined to Unconfined Flow? Analysis of Hydraulics in a Coastal River Delta” by Matthew Hiatt and Paola Passalacqua

What Controls the Transition from Confined to Unconfined Flow? Analysis of Hydraulics in a Coastal River Delta

Abstract Recent field work at the Wax Lake Delta (WLD) in coastal Louisiana indicates lateral outflow from channels to islands upstream of the receiving basin; in this region of the delta the flow ...

Sustainable deltas: livelihoods, ecosystem services, and policy implications

Coastal river deltas are dynamic and highly fertile landforms at the intersection of terrestrial and marine environments. They are often densely populated due to the opportunities for livelihood generation they offer, in particular, through agriculture and aquaculture production, but also for economic development and trade (Kuenzer and Renaud 2012). At the same time, and largely because they offer so many opportunities for development, many river deltas globally are threatened both by environmental and anthropogenic processes (Syvitski et al. 2009; Tessler et al. 2015; Szabo et al. 2015a). Deltas and their river basins are naturally dynamic systems, but human interventions in situ, such as urbanization, groundwater and hydrocarbon extraction, agricultural intensification, and channel regulation, and ex situ, including increased upstream water withdrawals, diversion and sediment trapping, increasingly combine with coastal hazards, such as sea level rise, salinity intrusion, and hurricanes to threaten delta social–ecological systems (e.g., Renaud et al. 2013). In combination, such processes exacerbate livelihood losses and existing inequalities, precipitate migration streams and often create new pockets of poverty, especially in urban centers within delta regions (Martin et al. 2013).

Habitat Characterization for Submerged and Floating-Leaved Aquatic Vegetation in Coastal River Deltas of Mississippi and Alabama

Habitat attributes of submerged aquatic vegetation and floating-leaved aquatic vegetation were analyzed from survey data collected in estuaries and coastal river systems of Mississippi and Mobile Bay, Alabama. The objectives were to: locate aquatic plant beds along tidally influenced areas and characterize landscape parameters of the sites; group the plant species into a manageable number of logical clusters; and characterize the landscape attributes indicative of the plant communities through Classification and Regression Tree (CART) analysis. Based on the cluster analyses, aquatic vegetation was categorized into three groups: (1) downstream estuarine/saline group, (2) brackish tolerant freshwater species group, and (3) upstream freshwater only group. Landscape features used for habitat characterization and plant classification were defined by long-term environmental conditions which would shape plant communities, rather than water quality parameters, such as water transparency and salinity, that exhibit higher variability and reflect the discrete conditions at time of sampling. The CART results suggest that salinity and “energy” (relative exposure to waves/currents) are the two most important abiotic factors that structure plant communities in the river deltas studied. Abstract: Atributos del habitat de vegetacion acuatica sumergida y vegetacion acuatica con hojas flotantes fueron analizados a partir de los datos de encuestas recogidas en los estuarios y sistemas fluviales costeras de Mississippi y la bahia de Mobile, Alabama. Los objetivos fueron: localizar camas de plantas acuaticas a lo largo de las zonas influidas por las mareas y caracterizar los parametros del paisaje de los sitios; Agrupar las especies de plantas en un numero manejable de agrupaciones logicos; y caracterizar los atributos paisajisticos indicativos de las comunidades de plantas a traves del analisis de arboles de clasificacion y regresion (CART). Con base en los analisis de agrupaciones, la vegetacion acuatica se clasifico en tres grupos: (1) Grupo de aguas abajo del estuario / solucion salina, (2) Grupo de especies de agua dulce tolerantes salobres, y (3) grupo de aguas arriba solamente agua dulce. Las caracteristicas del paisaje utilizadas para la caracterizacion del habitat y la clasificacion de plantas fueron definidas por las condiciones ambientales a largo plazo, que darian forma a las comunidades de plantas, en lugar de parametros de calidad del agua, tales como la transparencia del agua y la salinidad, que presentan una mayor variabilidad y reflejan las condiciones discretas en el momento del muestreo. Los resultados del CART analisis sugieren que la salinidad y “energia” (exposicion relativa a las ondas/corrientes) son los dos factores abioticos mas importantes que estructuran comunidades vegetales en los deltas de los rios estudiados.

Vulnerability assessments of coastal river deltas - categorization and review

Coastal river deltas are densely populated areas and hotspots of vulnerability. The delta’s ecological, social, and economic components are vulnerable to a wide variety of natural and anthropogenic threats. Sea level rise, climate variability, and rapid socio-economic development exert pressure on the already highly dynamic regions. To protect river deltas and their components, it is necessary to assess the degree of vulnerability so that mitigation efforts can be recommended to stakeholders and policy makers. Many such vulnerability assessments have been undertaken for river deltas. However, as vulnerability and related terms, such as resilience, coping-, and adaptive capacity only entered geosciences in the past decades, these terms are often used ambiguously. This makes it hard to compare existing studies, which not only interpret the related terms differently, but also consider completely different threats to deltas and their components, at different spatial and temporal scales. A comprehensive overview of studies addressing vulnerability of river deltas is missing. This paper presents a review, based on a consolidated set of definitions of vulnerability and related concepts in the context of coastal river deltas. All studies reviewed were categorized depending on their focus on either the ecologic, social, or economic component of river deltas, and were classified according to their spatial scale, temporal resolution, and numerous other research characteristics. Clear trends on dominant research foci in the field of river delta vulnerability could be extracted. Additionally, based on the findings presented here, recommendations for future assessments considering existing research gaps, are formulated.