The role of storm events in controlling chlorophyll distribution along the oligotrophic Rottnest continental shelf is examined data collected by autonomous ocean gliders combined with meteorological data. Spatial and temporal distribution of chlorophyll concentrations were obtained from a repeated transect across the shallow continental shelf that revealed complex relationships among wind events (e.g., differences in wind speed and direction) and chlorophyll concentrations. Data indicated that the water column responded rapidly to changes in wind speeds alternating between stratification, de-stratification and vice-versa over 1–3 days. Under low wind conditions (wind speeds < 7 ms–1), the water column was stratified and dense shelf water cascades (DSWC) was the dominant feature. The majority of DSWC events were associated with synchronous increases in chlorophyll and suspended sediment, often close to the seabed. During storm events (wind speeds > 15 ms–1) higher chlorophyll values were present throughout the vertically mixed water column. Maximum chlorophyll concentrations, more than double that due to climatology, were observed 1–3 days after the passage of storms subsequent to sediment re-suspension. Storm events, with an onshore component, promoted downwelling, the water column retained vertical stratification, and DSWC was present across the shelf. Here, DSWC intensified with higher chlorophyll in the cascaded water extending further offshore. It is concluded that wind speed and direction are the dominant parameters controlling the distribution of chlorophyll particularly during storm events.
Sea-level Rise, Coastal Flooding, and Storm Events
Tropical coral reef-lined coasts are exposed to storm wave-driven flooding. In the future, flood events during storms are expected to occur more frequently and to be more severe due to sea-level rise, changes in wind and weather patterns, and the deterioration of coral reefs. Hence, disaster managers and coastal planners are in urgent need of decision-support tools. In the short-term, these tools can be applied in Early Warning Systems (EWS) that can help to prepare for and respond to impending storm-driven flood events. In the long-term, future scenarios of flooding events enable coastal communities and managers to plan and implement adequate risk-reduction strategies. Modeling tools that are used in currently available coastal flood EWS and future scenarios have been developed for open-coast sandy shorelines, which have only limited applicability for coral reef-lined shorelines. The tools need to be able to predict local sea levels, offshore waves, as well as their nearshore transformation over the reefs, and translate this information to onshore flood levels. In addition, future scenarios require long-term projections of coral reef growth, reef composition, and shoreline change. To address these challenges, we have formed the UFORiC (Understanding Flooding of Reef-lined Coasts) working group that outlines its perspectives on data and model requirements to develop EWS for storms and scenarios specific to coral reef-lined coastlines. It reviews the state-of-the-art methods that can currently be incorporated in such systems and provides an outlook on future improvements as new data sources and enhanced methods become available.
Coastal flood risks are rising rapidly. We provide high resolution estimates of the economic value of mangroves forests for flood risk reduction every 20 km worldwide. We develop a probabilistic, process-based valuation of the effects of mangroves on averting damages to people and property. We couple spatially-explicit 2-D hydrodynamic analyses with economic models, and find that mangroves provide flood protection benefits exceeding $US 65 billion per year. If mangroves were lost, 15 million more people would be flooded annually across the world. Some of the nations that receive the greatest economic benefits include the USA, China, India and Mexico. Vietnam, India and Bangladesh receive the greatest benefits in terms of people protected. Many (>45) 20-km coastal stretches particularly those near cities receive more than $US 250 million annually in flood protection benefits from mangroves. These results demonstrate the value of mangroves as natural coastal defenses at global, national and local scales, which can inform incentives for mangrove conservation and restoration in development, climate adaptation, disaster risk reduction and insurance.
Global mean sea level budget is rigorously adjusted during the period 2005–2015. The emphasis is to provide the best estimates for the linear rates of changes (trends) of the global mean sea level budget components during this period subject to the constraint: Earth's hydrosphere conserves water. The newly simultaneously adjusted trends of the budget components suggest a larger correction for the global mean sea level trend implicated by the other budget components' trends under the budget constraint. The simultaneous estimation of the linear trends of the budget components subject to the constraint for closure improves their uncertainties and enables a holistic assessment of the global mean sea budget, which has implications for future sea level science studies, including the future Intergovernmental Panel on Climate Change (IPCC) Assessment Reports, and the US Climate Assessment Reports.
Coastal zones are among the most economically productive areas of the world. However, they are also among the most vulnerable regions to disasters triggered by natural hazards. Recent recognition of the role of healthy coastal and marine ecosystems for reducing vulnerability in coastal communities has led to the design of coastal management strategies that incorporate direct investments in these ecosystems. However, there is a lack of knowledge and understanding of the economic benefits of coastal and marine ecosystems for society, which has led to the degradation of these ecosystems and hindered the prospects of sustainable investments in coastal resilience projects, including green infrastructure.
In this paper, we analyze the economic importance and ongoing threats of the main marine and coastal ecosystems of the Wider Caribbean region, and identify the underlying economic causes of their deterioration. The need to improve coastal resilience in the Wider Caribbean has led to innovative approaches for the protection of coastal zones and their population from erosion and flood risk, prioritizing the role of marine and coastal ecosystems for coastal protection and vulnerability reduction in coastal communities.
Based on this review, we develop an analytical framework for economic analyses and impact evaluations of coastal restoration and protection programs, with the objective of allowing practitioners to properly identify the cost-effectiveness of nature-based solutions for coastal resilience.
Two adjacent estuaries in the northwestern Gulf of Mexico (GOM) (Mission–Aransas or MAE and Guadalupe–San Antonio or GE), despite their close proximity and similar extents of freshening caused by Hurricane Harvey, exhibited different behaviors in their post-hurricane carbonate chemistry and CO2fluxes. The oligotrophic MAE had little change in post-Harvey CO2 partial pressure (pCO2) and CO2 flux even though the center of Harvey passed right through, while GE showed a large post-Harvey increases in both pCO2 and CO2 flux, which were accompanied by a brief period of low dissolved oxygen (DO) conditions likely due to the large input of organic matter mobilized by the hurricane. The differences in the carbonate chemistry and CO2 fluxes were attributed to the differences in the watersheds from which these estuaries receive freshwater. The GE watershed is larger and covers urbanized areas, and, as a result, GE is considered relatively eutrophic. On the other hand, the MAE watershed is smaller, much less populous, and MAE is oligotrophic when river discharge is low. Despite that Harvey passed through MAE, the induced changes in carbonate chemistry and CO2 flux there were less conspicuous than those in GE. This study suggested that disturbances by strong storms to estuarine carbon cycle may not be uniform even on such a small spatial scale. Therefore, disparate responses to these disturbances need to be studied on a case-by-case basis.
Storm surge and sea level rise (SLR) are affecting coastal communities, properties, and ecosystems. While coastal ecosystems, such as wetlands and marshes, have the capacity to reduce the impacts of storm surge and coastal flooding, the increasing rate of SLR can induce the transformation and migration of these natural habitats. In this study, we combined coastal storm surge modeling and economic analysis to evaluate the role of natural habitats in coastal flood protection. We focused on a selected cross-section of three coastal counties in New Jersey adjacent to the Jacques Cousteau National Estuarine Research Reserve (JCNERR) that is protected by wetlands and marshes. The coupled coastal hydrodynamic and wave models, ADCIRC+SWAN, were applied to simulate flooding from historical and synthetic storms in the Mid-Atlantic US for current and future SLR scenarios. The Sea Level Affecting Marshes Model (SLAMM) was used to project the potential migration and habitat transformation in coastal marshes due to SLR in the year 2050. Furthermore, a counterfactual land cover approach, in which marshes are converted to open water in the model, was implemented for each storm scenario in the present and the future to estimate the amount of flooding that is avoided due to the presence of natural habitats and the subsequent reduction in residential property damage. The results indicate that this salt marshes can reduce up to 14% of both the flood depth and property damage during relatively low intensity storm events, demonstrating the efficacy of natural flood protection for recurrent storm events. Monetarily, this translates to the avoidance of up to $13.1 and $32.1 million in residential property damage in the selected coastal counties during the ‘50-year storm’ simulation and hurricane Sandy under current sea level conditions, and in the year ‘2050 SLR scenario’, respectively. This research suggests that protecting and preserving natural habitats can contribute to enhance coastal resilience.
Mangrove ecosystems are threatened by climate change. We investigated the effects of expected future (year 2100) drought intensities and rising sea levels on the spatial extent and biomass production of mangroves located along the southern Iranian semi-desert coastal areas of the Persian Gulf (PG) and the Gulf of Oman (GO) under the projections of the RCP 8.5 climate change scenario. To do so, we first needed to establish a robust link of past drought intensities to spatial extents and biomass amounts of mangroves in the study region that would enable the prediction of biomass for the climatic conditions projected by the RCP 8.5 scenario for the year 2100. Large differences in drought intensities in the past pointed to a coordinated wet (1986–1998) and a dry (1998–2017) period throughout the study area and resulted in strong correlations of drought intensity to spatial extents and above- and below-ground biomass amounts. Whereas landward mangrove margins expanded modestly during the wet and contracted severely during the dry periods, leading to variable net areal gains and losses over time, seaward mangrove margins retreated during both periods, presumably due to rising sea levels. By the end of the 21st century, predicted values of biomass per hectare in the remaining mangroves exceeded current values by 47–64% (above-ground) and 41–48% (below-ground) due to a reduced drought intensity predicted for the region. Assuming no landward expansion, predicted mangrove areas declined between 4.9 and 7.2% for every 10 cm rise in sea levels, resulting in a net loss of total mangrove biomass between 18 and 56% throughout the study region at a sea level rise of 100 cm. Variability among sites at all times was partly due to differences in drought intensities, coastal topographies, and differential rates of sedimentation and subsidence/uplift, with greater adverse effects on the coastal areas of the GO than the PG. We conclude that adverse effects of rising sea levels on the extent of mangroves were only partly offset by the increased biomass in the remaining mangroves following reduced drought severities predicted for the end of the 21st century. It is still unclear to what degree mangroves can take advantage of lesser drought intensities predicted for the end of the 21st century and expand their landward margins.
Climate change and its accompanying sea-level rise is set to create risks to the United States’ stockpile of spent nuclear fuel, which results largely from nuclear power. Coastal spent fuel management facilities are vulnerable to unanticipated environmental events, as evidenced by the 2011 tsunami-related flooding at the Fukushima plant in Japan. We examine how policy-makers can manage climate risks posed to the coastal storage of radioactive materials, and identify the coastal spent fuel storage sites that will be most vulnerable to sea-level rise. A geospatial analysis of coastal sites shows that with six feet of sea-level rise, seven spent fuel sites will be juxtaposed by seawater. Of those, three will be near or completely surrounded by water, and should be considered a priority for mitigation: Humboldt Bay (California), Turkey Point (Florida), and Crystal River (Florida). To ensure policy-makers manage such climate risks, a risk management approach is proposed. Further, we recommend that policy-makers 1) transfer overdue spent fuel from cooling pools to dry casks, particularly where located in high risk sites; 2) develop a long-term and comprehensive storage plan that is less vulnerable to climate change; and 3) encourage international nuclear treaties and standards to take climate change into account.
The fossil record provides valuable data for improving our understanding of both past and future reef resilience and vulnerability to environmental change. The spatial and temporal pattern of the initiation of the Holocene Great Barrier Reef presents a case study of reef response to rapid sea-level rise. Past studies have been limited by the lack of well-dated and closely spaced reef core transects and have not closely examined the composition of the reef-building communities through time. This study presents 80 new high precision U-Th and 5 radiocarbon ages from twelve new cores located along three transects across different geomorphic and hydrodynamic settings of One Tree Reef, southern Great Barrier Reef, to document three distinct stages of Holocene reef development in unprecedented detail. Temporal constraints on changing paleoecological assemblages of coral, coralline algae and associated biota revealed three distinct phases of reef development, consisting of: 1) a fast, shallow and clear-water reef initiation from 8.3 until 8 ka; 2) a shift to slower, deeper and more turbid-water reef growth from 8-7 ka; and 3) a return to shallow and rapid branching coral growth in clear-water conditions as the reef “catches up” to sea-level. A minimum lag prior to reef initiation of 700 years was identified, which differs in length depending on reef environment and Pleistocene substrate height. In this new model, reef growth initiated on the topographically lower leeward margin and patch reef, prior to the start of windward margin development, contrary to the traditional reef growth model. While there was a shift to conditions less favorable for reef growth at 8 ka, this did not prevent the slow accretion of more sediment-tolerant coral communities. The majority of the reef reached sea level by ~6 ka. This new conceptual model of Holocene reef growth provides new constraints on changes in paleoenvironment that controlled reef community composition and growth trajectories through sea-level rise following inundation.