Sea Level Rise - the Consequences and Adaptation

This piece is a continuation of the Sea Level Rise – the Science post on the Nature page. Let us attempt to see in this piece how different thoughts are taking shape to face the reality of the consequences of sea level rise (SLR). The consequences are expected across the board – in both biotic and abiotic systems. But to limit this blog to a manageable level, I will try to focus – in an engineering sense – on some aspects of human livelihood in frontal coastal areas – some of the problems and the potential ways to adapt to the consequences of SLR (In a later article Warming Climate and Entropy, posted in December 2019 – I have tried to throw some lights on the climate change processes of the interactive Fluid, Solid and Life Systems on Earth – the past, the present and the future).
Before doing that let us revisit one more time to point out that all familiar lives and plants have a narrow threshold of environmental and climatic factors, within which they can function and survive. This is in contrast to many microorganisms like Tardigrades, which can function and survive within a wide variation of factors. Therefore adaptation can be very painful, even fatal when stresses exceed the thresholds quickly – in time-scales shorter than the natural adaptation time.
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1. SLR Imposition
1.1 Stress
What is stress? Global warming and SLR literature use this term quite often. Stress is part of the universal cause-effect, force-response, action-reaction, stress-consequence duo. In simple terms and in context of this piece, global warming is the stress with SLR as the consequence – in turn SLR is the stress with the consequences on human livelihood in the coastal zone.          
Again, as I have mentioned in the previous piece, the topic is very popular and literature are plentiful with discussions and opinions. The main resources consulted for this piece are the adaptation and mitigation chapters of the reports worked on by: UN entity IPCC (Intergovernmental Panel on Climate Change), US NOAA (National Oceanic and Atmospheric Administration), and USACE (United States Army Corps of Engineers).
1.2 Vulnerability
Before going further, it will be helpful to clarify the general meanings of some of the commonly used terms – these terms are used in contexts of system responses and reactions – susceptibility, prevention, the ability to adjust to changes, and the ability to cope with repeated disruptions. The first is vulnerability – the susceptibility and inability of a system to cope with adverse consequences or impacts. One can simply cite an example that human habitation, coastal and port infrastructure in low lying areas are more vulnerable to SLR than those lying in elevated areas – and so are the developing societies than the developed ones. 
1.3 Mitigation
The second is known as mitigation – the process of reducing the stresses to limit their impacts or consequences. We have seen in the NATURE page that there could be some 8 factors responsible for SLR. But scientists have identified that the present accelerated SLR is due to the continuing global warming caused by increased concentration of greenhouse gases. This anthropogenic factor is in human hands to control; therefore reducing greenhouse gases is one of the mitigation measures.  
1.4 Adaptation
The third is adaptation – the process of adjusting to the consequences of expected or imposed stresses, in order to either lessen or avoid harm, or to exploit beneficial opportunities. This is the primary topic of this piece – how humans could adjust to the consequences of SLR. The fourth is closely related to adaptation and is known as resilience – the ability to cope with repeated disruptions. It is not difficult to understand that adaptation process can become meaningless without resilience.
Also to note that a successful mitigation can only work with some sort of adaptation – for example, adaptation by innovating new technologies to control and limit greenhouse gas emission. However, one may often require to compromise or make trade-offs between mitigation and adaptation processes to chalk out an acceptable solution.
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2. SLR Consequences
I have included an image (credit: anon) of human habitation and township developed on a low lying barrier island. Similar developments occur in most coastal countries – some are due to the pressure of population increase, while others are due to the lack of foresight and understanding by regulating authorities. Such an image is important to look at, to reflect on and to think about human vulnerability, and the processes of mitigation, adaptation and resilience to the consequences of SLR. A series of ASCE Collaborate discussions gives a glimpse of SLR on low-lying airports. 
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2.1 Enhanced Wave Activity
Before going further, some aspects of climate change that exacerbate the SLR effects need to be highlighted. The first is the enhanced wave activity associated with SLR. We all have seen the changing nature of waves sitting on a shoreline during an unchanging weather condition – less wave activity at low tide and enhanced waves as tide rises. Why does that happen? One reason is the depth-limited filtering of wave actions – for a certain depth only waves smaller than about 4/5th of water depth could pass on to the shore without breaking. Therefore, as the water level rises with SLR, the numbers of waves propagating on to the shore increase.
The second is the enhanced storminess caused by global warming. All the climate change studies indicate the likelihood of increase in storminess both in intensity and frequency – and perhaps we are witnessing symptoms of that already. High wind storms are accompanied by high storm surges and waves together with torrential rainfall and terrestrial flooding.
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2.2 Inundation and Others
What are other consequences of SLR? The consequences are many – some may not even be obvious at the present stage of understanding. They range from transgression of sea into the land by erosion, inundation and backwater effect, to salt-water intrusion, to increased forces on and overtopping of coastal waterfront structures.  
If the 2.0 meter SLR really (?) happens by the end of the 21st century, then it is impossible for one not to get scared. I have included a question mark to the 2.0 meter SLR because of the high level of uncertainty in the predictions by different organizations (see the Sea Level Rise – the Science blog on the NATURE page). For such a scenario, the effective SLR is likely to be no less than 10.0 meter affecting some 0.5 billion coastal population. The effective SLR is an indication of the range of consequences that a mean SLR would usher in.     
Let me try to provide a brief outline of the consequences. First, one should understand that the transgression of sea into the land is not like the invasion by a carpet of water gradually encroaching and inundating the land. It is rather the incremental incidences of high-tide-flooding combined with high wave activity. The result is the gradual net loss of land into the sea through erosion and scour, sediment-morphological readjustments and subsequent submergence.                   
What adaptation to SLR really means? Let us think of coastal population first. Survival instinct will lead people to abandon what they have, salvage what they can, and retreat and relocate themselves somewhere not affected by SLR. Although some may venture to live with water around if technological innovations come up with proven and viable measures. There are many traditional human habitations in seasonally flooded low lands, and also examples of boathouses around the world. Therefore, people’s lives are not so much at stake in direct terms; it is rather the monetary and emotional losses they would incur – losses of land, home and all of their valuable assets and memories. This adaptation process will not be equally felt by all the affected people. Rich people and perhaps many in developed societies are likely to cope with the problem better than the others.
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2.3 Civil Infrastructure
Perhaps the crux of the problem will be with civil infrastructure. One can identify them as four major types:

1. coastal defense structures (e.g. dikes, seawalls, revetments and groins);
   
2. port and harbor infrastructure (e.g. breakwaters, quays, wharves and jetties, and dolphins);
   
3. city and county utility infrastructure (e.g. drainage outlets, bridges and culverts and coastal roads), and
   
4. homesteads.
   

The problem infrastructure will also include various nearshore and offshore in-water oil platforms and facilities. There is no denying that all these structures standing at the waterfront and in-water will become vulnerable to the water forces high in magnitude and frequency – with enhanced slamming and increased incidences of overtopping and scour. City drainage and disposal outlets will be additionally affected by backwater effects. These stresses are likely to gradually undermine the functionality and failure of structures.
Some other aspects of the problem lie with the intrusion of sea saline water into estuaries, inlets and aquifers. Coastal manufacturing and energy facilities requiring freshwater cooling will require adapting to the SLR consequences. The problem will also be faced with the increased corrosion of structural members.
What to do with this huge problem of the existing civil infrastructure? What does adaptation mean for such a problem? One may think of renovation and reinforcement, but the likelihood of success of such an adaptive approach may be highly remote. How do the problems translate to the local and state’s economy? What about abandoning them to form submersed reef – declaring them as Water Park or sanctuary? - leaving many as remnants for posterity like the lost city of Plato’s (Greek Philosopher, 423 – 347 BCE) Atlantis? There are no easy answers to any of these questions; but there is no doubt that stakes are very high. We can only hope that such scenarios would not happen.
What is important and is being initiated across the board is the formulation of mitigation and adaptation strategies and policies. Such decision making processes rely on the paradigm of risk minimization – but can only be meaningful if uncertainties associated with SLR predictions are also minimized. One important area of work where urgent attention is being paid is in the process of updating and redefining the standards, criteria and regulations required for robust planning and design of new coastal civil infrastructure. However, because of uncertainties in SLR predictions even this process becomes cumbersome. Placing concrete and steel to build anywhere is easy, what is not easy is envisioning the implications and the future. Here is a ASCE Forum Discussion Piece on climate conditions non-stationarity, and implications for relevant civil engineering standards.
Apart from the 2017 NAP Proceedings – 24847 Responding to the Threat of Sea Level Rise, the 2010 publication – 12783 Adapting to the Impacts of Climate Change is an excellent read on possible options – as approaches to adapt to different stresses and consequences imposed by climate change. 
Well, some thoughts in a nutshell, shall we say? But mitigation of and adaptation to a complex phenomenon like global warming, climate change and SLR must be understood as an evolving process – perfection will only likely to occur as things move forward. And one should not forget that the SLR problems as complex and intimidating as they are, are slow in human terms – therefore the adaptation processes should be conceived in generational terms, but all indications suggest that the thinking and processes must start without delay. Fortunately all members of the public are aware of the problem and are rightly concerned - whether or not things are rolling in the right direction. Hopefully, this will propel leaders to take thoughtful actions.
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3. An Overview of the 2021 IPCC Assessment
What does the 2021 IPCC – AR6 say about the risks associated with SLR?
In its WGII Technical Summary – probable risks posed by enhanced sea level rise – have been spelled out in different confidence scales. The assessments and predictions are based on field observations/evidences and climate modeling efforts of different sorts (see modeling basics in Water Modeling). And three other WIDECANVAS articles: Warming Climate and Entropy, Uncertainty and Risk and The World of Numbers and Chances can help understanding the IPCC scale. This qualitative scale is defined in a matrix of evidence vs agreement – with the agreement indicating the degree of conformity between observations and the results of analytical tools or models. When an assessment is rated up to a sufficiently defensible scale – it is subjected to quantification in a way to define the probability of occurrence and labeling it in likelihood terms.
Here is a gist of IPCC findings and suggestions:
Coastal risks will increase by at least one order of magnitude over the 21st century due to committed sea level rise impacting ecosystems, people, livelihoods, infrastructure, food security, cultural and natural heritage and climate mitigation at the coast. Concentrated in cities and settlements by the sea, these risks are already being faced and will accelerate beyond 2050 and continue to escalate beyond 2100, even if warming stops. Historically rare extreme sea level events will occur annually by 2100, compounding these risks (high confidence) . . .
Under all emissions scenarios, coastal wetlands will likely face high risk from sea level rise in the mid-term (medium confidence), with substantial losses before 2100. These risks will be compounded where coastal development prevents upshore migration of habitats or where terrestrial sediment inputs are limited and tidal ranges are small (high confidence). Loss of these habitats disrupts associated ecosystem services, including wave-energy attenuation, habitat provision for biodiversity, climate mitigation and food and fuel resources (high confidence). Near- to mid-term sea level rise will also exacerbate coastal erosion and submersion and the salinisation of coastal groundwater, expanding the loss of many different coastal habitats, ecosystems and ecosystem services (medium confidence) . . .
The exposure of many coastal populations and associated development to sea level rise is high, increasing risks, and is concentrated in and around coastal cities and settlements (virtually certain). High population growth and urbanisation in low-lying coastal zones will be the major driver of increasing exposure to sea level rise in the coming decades (high confidence). By 2030, 108–116 million people will be exposed to sea level rise in Africa (compared to 54 million in 2000), increasing to 190–245 million by 2060 (medium confidence). By 2050, more than a billion people located in low-lying cities and settlements will be at risk from coast-specific climate hazards, influenced by coastal geomorphology, geographical location and adaptation action (high confidence) . . .
Under all climate and socioeconomic scenarios, low-lying cities and settlements, small islands, Arctic communities, remote Indigenous communities and deltaic communities will face severe disruption by 2100, and as early as 2050 in many cases (very high confidence). Large numbers of people are at risk in Asia, Africa and Europe, while a large relative increase in risk occurs in small island states and in parts of North and South America and Australasia. Risks to water security will occur as early as 2030 or earlier for the small island states and Torres Strait Islands in Australia and remote Maori communities in New Zealand. By 2100, compound and cascading risks will result in the submergence of some low-lying island states and damage to coastal heritage, livelihoods and infrastructure (very high confidence). Sea level rise, combined with altered rainfall patterns, will increase coastal inundation and water-use allocation issues between water-dependent sectors, such as agriculture, direct human consumption, sanitation and hydropower (medium confidence) . . .
Risks to coastal cities and settlements are projected to increase by at least one order of magnitude by 2100 without significant adaptation and mitigation action (high confidence). The population at risk in coastal cities and settlements from a 100-year coastal flood increases by approx. 20% if the global mean sea level rises by 0.15 m relative to current levels, doubles at 0.75 m and triples at 1.4 m, assuming present-day population and protection height (high confidence). For example, in Europe, coastal flood damage is projected to increase at least 10-fold by the end of the 21st century, and even more or earlier with current adaptation and mitigation (high confidence). By 2100, 158–510 million people and USD7,919–12,739 billion in assets are projected to be exposed to the 1-in-100-year coastal floodplain under RCP4.5, and 176–880 million people and USD8,813–14,178 billion assets under RCP8.5 (high confidence). Projected impacts reach far beyond coastal cities and settlements, with damage to ports potentially severely compromising global supply chains and maritime trade, with local to global geopolitical and economic ramifications (medium confidence). Compounded and cascading climate risks, such as tropical cyclone storm surge damage to coastal infrastructure and supply chain networks, are expected to increase (medium confidence) . . .
Particularly exposed and vulnerable coastal communities, especially those relying on coastal ecosystems for protection or livelihoods, may face adaptation limits well before the end of this century, even at low warming levels (high confidence). Changes in wave climate superimposed on sea level rise will significantly increase coastal flooding (high confidence) and erosion of low-lying coastal and reef islands (limited evidence, medium agreement). The frequency, extent and duration of coastal flooding will significantly increase from 2050 (high confidence), unless coastal and marine ecosystems are able to naturally adapt to sea level rise through vertical growth and landward migration (low confidence). Permafrost thaw, sea level rise, and reduced sea ice protection is projected to damage or cause loss to many cultural heritage sites, settlements and livelihoods across the Arctic (very high confidence). Deltaic cities and settlements characterised by high inequality and informal settlements are especially vulnerable (high confidence). Although risks are distributed across cities and settlements at all levels of economic development, wealthier and more urbanised coastal cities and settlements are more likely to be able to limit impacts and risk in the near- to mid-term through infrastructure resilience and coastal protection interventions, with highly uncertain prospects in many of these locations beyond 2100 (high confidence). Prospects for enabling and contributing to climate resilient development thus vary markedly within and between coastal cities and settlements (high confidence).
RCP stands for Representative Concentration Pathway.
One can pass detailed review comments on many of the IPCC findings and suggestions. Let us not go in that direction – instead, I will point to some crucial aspects that escaped IPCC reporting and investigations. In brief, these omissions include: SLR induced enhancement of and changes in the water motion dynamics along coastal waterfront and shores. These are likely to be manifested in such areas as – wave, tide, circulation, extreme events like storm surge and tsunami, and shoreline changes associated with sediment-morphology dynamics due to such forcing. What are the characterizations of such crucial changes? What are the impacts of SLR on the probable redistribution and enhancement of Force Fields in a Coastal System, and associated implications?
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Here is an anecdote to ponder:
The disciple said, “Sir, adaptation is a very strong word perhaps more than what we think it is.”
The master replied, “Yes, it does have a deeper meaning. One is in the transformation of the personalities undergoing the adaptation processes. It is a slow and sequential process ensuring the fluidity of Nature and society and evolution. If one thinks about the modern age of information, travel and immigration, the process is becoming much more encompassing – perhaps more than we are aware of. But while slow adaptation is part of the natural process, the necessity of quick adaptation can be very painful and costly.”

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- by Dr. Dilip K. Barua, 29 September 2016

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