Tomorrow's Coasts: Complex and Impermanent

Most people tend to think of coasts as material “things”. What you see when you look at a coast at any instant in time may be a beach composed of sand or a coastal wetland consisting of vegetation, mud and crabs and perhaps some methane or hydrogen sulfide gas. But in previous times it may have been very different and it probably will be different in the future. In reality, coasts are not “things” but processes; they are not static but are constantly becoming something new. This has always been the natural way with coasts. The ever-changing coastal process involves the interplay of solid material (e.g., sand and mud), chemistry (e.g., the pH of the Earth’s oceans), forces, energy fluxes and transfers (e.g., physical, chemical, biological, and solar), biological activity and ecological evolution, and, now, profound human interaction. We may reasonably expect coastal change to be accelerated in response to the climate changes that are now underway in the Anthropocene, a new geologic epoch in which human activities are causing profound and enduring modifications to the earth’s surface.

Coastal environments are changing throughout the world. Climate is only one of several drivers of change. Collectively, the suite of worldwide changes constitutes what is popularly referred to as “global change”. While climate is an essential and prominent member of that suite of changing environmental conditions, it is not the only thing that is changing or likely to change. In addition to increases in greenhouse gases, human contributions include several other anthropogenic sources of change that are less well-known.

Seas are rising and seriously impacting coasts and coastal communities globally. Global warming is causing melting of glaciers and steric expansion of water volume. Locally and regionally, other effects including land subsidence and the slowing of ocean currents such as the Gulf Stream are causing additional rises. By midcentury, relative sea levels in cities like New York and Miami may exceed those of the year 2000 by up to 1.2 m (~ 4 ft.).

River deltas were the cradles of early civilizations and are currently the habitats of 500 million people. But river deltas worldwide are sinking and being invaded by rising seas. The effects of sea level rise and floods are greatly exacerbated by subsidence and human modifications including reductions in supply of sediment and the extraction of water, oil and gas from deltaic sediments as well as damaging engineering works.

The shape of the land and the processes that mold the land are mutually interconnected and change together as a complex system. The coupled suites of mutually-inter-dependent hydrodynamic, biologic and anthropogenic processes, seafloor and landscape morphologies interact to cause time-dependent sequences of change. In many cases it is moving water or air (currents, waves, winds) that redistribute the material. The new land configurations in turn then alter the directions, intensities and gradients of the moving water or air. In other cases, it is biological rather than physical processes that build or degrade morphologic features such as coral reefs or coastal marshes. There is constant feedback among the multiple components of the system.

People are integral parts of nature and, in many respects, are becoming dominant parts. This notion is implicit in the term “Anthropocene”. In no environment is the connection between people and nature more apparent than in coastal systems. Mutual causality between humans and nature plays out there on a daily basis, sometimes in very positive ways and other times in tragic ways. The enjoyment of coastal beauty and spiritual stimulation are among the positive attractions as are access to global seaways, fisheries and recreation. Death, disease and destruction wrought by severe storms and tsunamis are paramount among the downsides. But for a multiplicity of reasons, roughly half of the world’s 7 billion people live within 100 km (60 miles) of the shore. And the activities of those who live much farther inland, for example within the catchments of large rivers that run to the coast, impact the coastal environment and its residents in numerous ways. Human activities that directly impact coastal systems include urbanization, agriculture, nutrient runoff, engineering works, fisheries, oil and gas production, dredging and various forms of pollution. Natural processes that impact coastal residents include sea level rise, storms and storm surges, water-borne pathogens, tsunamis, and loss of ecosystem services. Important ecosystem services include pollination, decomposition, water purification, erosion and flood control, carbon storage, and climate regulation.

According to NOAA’s Office of Coastal Management, inundation events are the dominant causes of natural-hazard-related deaths in the U.S. and are also the most frequent and costly of the natural hazards affecting the nation. The effects of inundation in other nations such as Bangladesh, Indonesia, Thailand and India are often devastating. While the long-term rises in mean sea level as discussed in Part 1, Chap. 3 are instrumental in allowing inundation to reach farther inland and to ever higher elevations, it is the short-lived episodic, non-tidal, events that cause the most damage. Included among these inundation causes are tsunamis, storm surges, coastal flooding caused by onshore winds and wave-induced set up, river and inland flooding and extreme rainfall events. The deepest flooding occurs when two or more of these phenomena reinforce each other and coincide with perigean spring high tides (aka. “king tides”). For example, it is common for tropical cyclones to bring storm surges along with heavy rainfall and wave induced set up of mean water level. Structures such as levees that are designed to protect can also impede the return of floodwaters once overtopped. Navigation channels can also provide funneling pathways for surges.

Coastal ecosystems are important for fisheries as fish nurseries and provide people with food security as well as livelihood opportunities. These areas, which include mangrove forests, coral reefs, and submerged aquatic vegetation beds, may be degraded by natural and anthropogenic events. Rich in species, coastal ecosystems are essential in storing and cycling nutrients, protecting shorelines, and filtering pollutants. The degradation of coastal ecosystems imperils species that rely on this habitat. Natural hazards such as tropical cyclones, climate fluctuations, and flooding cause ecosystem degradation. Coastal ecosystems have been exploited for development, recreation, and industry, worldwide. Over population, pollution, destruction of mangroves and coral reef for development, and overfishing degrade their health. Recent research has provided managers with a better understanding to plan and execute restoration projects. Marine protected areas have demonstrated the importance of monitoring restorations and recovery.

The margins of the sea are encroaching landward throughout most of the world. This is happening not simply because of sea level rise but also because the solid material- sand, mud, gravel-composing the shore and the subaerial and subaqueous lands immediately adjacent to it is being displaced. In addition to physical erosion by wave, thermal erosion in the Arctic and loss of wetlands through ecological processes are also active. The expected rate of sea level is predicted to exceed critical “tipping points” for wetlands destruction in many regions.

Floods are among the most common natural hazards with complex and far-reaching impacts. Coastal floods are most often caused by storm surge (coastal), rivers that exceed their flood stage capacity (fluvial), and torrential rainfall (pluvial). Increasingly, compound flooding by all three causes is the most severe. The adverse consequences of flood events, especially coastal flooding, to human health. Drowning is the major cause of death, followed by heart attacks, hypothermia, blunt trauma caused by wind-borne objects and vehicle-related accidents. Snakebites, electrocution and wound infections are also causes of death. Less obvious health impacts involve diseases and toxins spread by water and water-nurtured vectors (e.g. mosquitos).

The ocean is life sustaining. But, it is also a mighty force which can pose great danger to those living along its coasts. As a means of protection, we’ve armored our coastlines with grey infrastructure. However, these structures are expensive to build and maintain, encourage further development in areas particularly susceptible to flooding and storm damage, and often fail. In order for coastal communities across the globe to survive in a climate-changed future, nature must be prioritized in our regulatory, financial, and social systems in ways which empower, encourage, and incentivize smart and necessary investments in natural infrastructure.

By 2015, the Pearl River Delta urban agglomeration had overtaken Tokyo as the world’s largest megacity. The Pearl River Delta is sinking at an average rate of 2.5 mm/year. This subsidence, combined with rising sea level, increased intensity of impact from typhoons and storm surge and projections for increased urban expansion have placed Guangzhou at, or near the top of the list of the world’s most threatened coastal cities.

Coastal Louisiana owes its existence entirely to sediments supplied to the Gulf of Mexico coast by the Mississippi River. Today, land loss greatly exceeds land creation. The extensive engineering works that were intended to protect people and assets from floods and support navigability of the lower Mississippi River are now profoundly implicated in the disappearance of the wetlands that once provided natural protections. The loss of wetlands, barrier islands and other lands in coastal Louisiana is severe and becoming worse.

The entire coast of Florida is vulnerable to rising sea levels, storm surges, and episodic inundation. The threatened assets on the highly developed and urbanized southeast coast include expensive high-rise hotels and condos while those on the “Nature Coast” fronting the Gulf of Mexico are primarily unique natural ecosystems. Both coasts are already experiencing recurrent inundation for different reasons. Model projections, suggest that by 2050 Miami sea levels could be up to 1 meter higher than at present. Land losses on the highly sensitive Gulf Coast could involve eastward displacement of the coast by several kilometers.

The Mid-Atlantic Bight (MAB) extends alongshore, from Cape Cod, MA to Cape Hatteras, NC and includes major estuarine systems such as Narragansett Bay, Long Island Sound, Chesapeake Bay and Pamlico Sound. Sea level rise continues to have a dramatic effect on developed watersheds and urban estuaries, which are common to this highly populated region. Tropical cyclones contribute to flooding, which impacts coastal roads, homes, farms, and even fresh water supplies. Research is being applied to improve our understanding of the physical processes that connect estuaries and the coastal ocean and better forecast floods. Advances will result in improved marine policies and coastal resilience.

Near-surface air temperatures in the Arctic are rising 2 to 3 times faster than are temperatures elsewhere on the earth’s surface. In the near future, the Arctic ocean is likely to become ice free in the summer. While this may be good from the perspective of navigation, it is bad from the perspectives of the unique Arctic ecosystem and Native Alaskan subsistence, health and culture, which are tightly bound to, and dependent on, a frozen ocean and frozen permafrost on land.

Numerical models are essential tools to address many environmental issues including inundation, hypoxia, and harmful algal blooms. Scientists and engineers are continuing to develop models to simulate and forecast events of various space and time scales. New computational and networking capabilities are key to developing coupled models that will provide users with accurate environmental information, including uncertainty and probabilities. Increasing computing power allows a similar increase of spatial and temporal resolutions in coastal ocean models. Multidisciplinary and integrated modeling projects are improving our understanding of the interactions between physical and biogeochemical and biological phenomena. Model verification and validation is an essential component in producing accurate and credible models that highlight how ocean processes are shaping modern coastlines.

It is imperative for humanity to anticipate and plan better for the future impacts of climate change and coastal flooding on low-income, elderly and infirm communities living in flood-prone areas. As sea levels rise, low-lying vulnerable urban areas throughout the world will be more frequently flooded by storms. Low-income families will be forced to move into higher density areas or to low-lying, flood-prone areas. There is growing vulnerability of impoverished people living coastal cities, particularly coastal megacities, to the impacts of climate change. Education and awareness along with regionally specific adaptive management policies are probably the most effective tragedy preventers.

Many coastal regions constitute “contested spaces”. Potential consequences of climate change is bringing another set of pressures for communities and decision-makers to understand as they review and deliberate on options and set priorities for management action. Underpinning the decision-making process is a recognition of the values of those with particular interests at stake in any given location. Social conflicts arise from these different interests such as between landowners seeking to protect private property and those with a passion to ensure public good values are retained. Governments should be in a position to develop legislation that address all these interests in the context of long-term changes to coastal environments driven by natural forces knowing that frequently these forces are modified by human interventions. It is vital for science to have an input into the various stages of adaptive coastal management to ensure the consequences of existing and future human actions do not have adverse environment, social and economic consequences. Scientists should be willing to engage at all these stages from policy, law-making, implementation and enforcement and to monitor outcomes of actions so that in future improvements can be made. Their experience with field observations of coastal change, experiments in coastal processes, and modelling of long-term impacts are seen as important inputs in alerting governments and communities to those likely consequences of operating in a climate changing coastal world. This means that for adaptive coastal management in many countries to be effective coastal scientists should be prepared to move beyond the comfort zone of their disciplinary confines no matter how frustrating and painful it may be at times.

Big data has the potential to enhance decision-making among individuals and communities. More specifically, combining human and physical big data into models can inform decisions during weather-related hazards and potentially reduce uncertainty resulting from climate change. This chapter provides some insights about the expansion of big data and its potential to enhance adaptation efforts given rapid environmental changes, specifically those occurring in coastal areas.

There are three categories of actions that humans need to take in order to minimize the detrimental impacts of global change on tomorrow’s coastal systems. The first, of course, is to cause less harm by reducing our carbon footprint and ceasing to do destructive things like polluting, dredging, severing sediment supply, withdrawing groundwater, overdeveloping etc. Much has been written and spoken about this even though we have said relatively little about it in this book. The second category of actions, which has received minimal attention from the popular media but has been the motivating theme of this book, involves promoting deep enough understanding of the myriad complex interconnections of coastal processes to allow long-term predictions of what may lie ahead. Such predictions are essential to evolving effective strategies for adapting and remaining resilient. The third action is to ensure that to the extent possible we embed coastal science, including matters related to future impacts of climate change, into state and federal policies and law. The aim must be to ensure that regional coastal strategies are based on the best available science to reduce risk to built and natural assets from the adverse effects of short-term practices driven by local vested interests.