Overuse harms habitatsThe appeal of the coasts is explained to a great extent by the large number of ecosystem services that they provide. In past decades the power of this attraction led to many coastal regions becoming increasingly heavily populated and pressured beyond their carrying capacity – be it through excessive fishery or the challenges of wastewater treatment. By using the coasts unsustainably, people harm themselves in the end because there will come a time when certain ecosystem services can no longer be provided.
One example is the development of mass tourism in many locations. Coastal regions want to attract holidaymakers to their beaches with attractive landscapes and clean water, yet obtrusive hotel-building destroys the pristine appearance of the landscape, while immense quantities of wastewater from the hotel complexes cause water pollution. This is how overuse blights the recreational value of a landscape, undermining its provision of cultural ecosystem services.
Hard-to-pinpoint threatsSome forms of overuse are not always easy to identify and measure. Humans and the environment are closely interwoven in socio-ecological systems. Coastal regions extend over vast areas between land and sea and are very difficult to define in precise spatial terms. There can also be a lengthy time lag between cause and effect.
One example is the industrial use of polychlorinated biphenyls (PCBs): chlorine compounds that were used until the end of the last century in transformers, in hy-draulic fluids and as softeners in sealants and plastics. Because they were applied in such diverse uses, significant quantities found their way into the environment. Only in the early 1970s was it recognized that the substances are toxic and have carcinogenic effects. Moreover, it was observed that in sea mammals such as seals they cause pathological changes to the uterus. This has resulted in a drastic decline in the number of successful seal births in the North Sea and the Baltic, particularly since the 1970s. Finally, in 2001 the use of PCBs was prohibited by the Stockholm Convention, an international treaty to protect the environment from particularly dangerous chemicals. Thus, several decades elapsed between the actual cause, the emergence of the environmental problem, the identification of the substances and the systematic ban on their use.
Ever expanding megacitiesWithin socio-ecological systems where people live in large numbers or sources of pressure are multifarious, the interactions can be especially complex and in many cases difficult to discern. Today this applies particularly to coastal megacities of over 10 million inhabitants. Such regions are characterized by high population density and high-density building development. Many people need to be supplied with fresh water, food and electricity, which imposes high demands upon infrastructure, logistics and waste disposal. Because people from poorer rural regions inland are constantly moving to the coastal megacities in search of work or training, these metropolitan centres will continue to grow in future – above all in Africa, South America and South East Asia.
- 2.28 > Many of the megacities of the future, cities of over 10 million inhabitants, are in Asia and Africa.
Aquifer The term “aquifer” denotes a subsurface body of rock containing pore spaces through which groundwater flows.2.30 > Tokyo managed to halt its land subsidence from the mid-1970s, unlike most other cities.
- One of the biggest problems in the wake of this continuous urbanization has been the increasing frequency of floods affecting entire urban districts. Flooding can be caused both by heavy rainfall events and by storm surges in the sea level. Apart from the immense economic damage caused by floods, they pose a very real risk to life and limb. Interestingly, so far these have been attributable not so much to global climate change and sea-level rise than to bad urban planning. The following causes have been identified:
- Subsidence due to building density: the construction of high-rise buildings and other large structures has significantly increased the load on the ground. Under the heavy weight, the densely built-up sites slowly subside.
- Subsidence due to groundwater abstraction: because ponds, lakes and rivers at ground level in many coastal cities are heavily polluted by untreated wastewater and detritus, they cannot be used as sources of drinking water. Drinking water for many millions of inhabitants therefore has to be abstracted from the groundwater in the deeper geological rock layer, the aquifer. Since groundwater normally acts as a natural abutment against the downward force of buildings, pumping it away in large quantities exacerbates the subsidence of densely built-up areas. Construction measures themselves also lead to a fall in the groundwater level. Deep excavations are made for large buildings and any water that penetrates is pumped out, with the result that the ground in the excavations settles and the pore volume that was previously filled by the groundwater shrinks. The land surface then sinks.
- Construction on low-lying river catchments and marshlands: many of the migrants to cities from poorer rural regions settle at the growing periphery of the cities in what are known as informal settlements. These are often located in low-lying areas that are unsuitable for building development, which are frequently along the banks of rivers or on marshes and meadows at especially high risk of flooding.
- Poor sewer construction: in many cities, developments have been built across natural watercourses or flood-prone areas such as alluvial plains. As a result, natural rainwater drainage areas have disappeared in many places. Added to that, surfaces have been sealed by the construction development so that rainwater no longer has much seepage area, but drains away torrentially instead.
- Natural subsidence: in some coastal regions the land is slowly sinking naturally. There can be a number of causes for this. For example, in some areas the land mass may slowly subside due to the movement of a continental plate. In other coastal areas, particularly in river deltas, the ground sinks because sediment layers become more densely packed over time and sag under their own weight.
- 2.29 > Many of the world’s largest cities are sinking today, primarily due to groundwater abstraction and massive building development. In many cities this subsidence will continue into the future.
2.31 > Inundation of an entire industrial zone in the province of Ayutthaya, north of the Thai capital of Bangkok, in November 2011. Among those affected by the disaster is a Japanese car manufacturer based there.
A sinking metropolisAn extreme example of a sinking city is Jakarta, the capital of Indonesia, which is currently the fastest sinking metropolis in the world. Particularly since the 1980s the city has grown drastically in terms of both population and road and building construction – especially high-rise buildings. In 2015 Jakarta already had at least 10 million inhabitants, and its population is forecast to reach 13.8 million by the year 2030.
Jakarta is in a very low-lying region, partly on peaty soils. The densely developed northern area, with its many high-rise buildings, and the commercial centre in particular are sinking in the soft subsurface – currently by up to 10 centimetres a year. The abstraction of groundwater for drinking water supply is also contributing to this effect, and it is feared that the sinking will accelerate. Without countermeasures and a reduction of groundwater abstraction, by the year 2025 parts of Jakarta are likely to have sunk by a further 180 centimetres.
Floods occur with growing frequency, leaving the city’s highways and commercial centre half a metre under water, both after heavy rainfall events and higher than usual sea water levels. Natural watershed and floodplain areas have been built upon repeatedly over time so that rainwater has almost nowhere to seep away. The alarming fact today is that more and more people are affected by the floods. New arrivals in the city predominantly settle close to the economically attractive north of the city. This increases their prospects of finding work or reduces the length of the commute to their workplaces.
- 2.32 > Jakarta is currently the world’s fastest sinking metropolis. Because the city pumps groundwater on a large scale for its drinking water supply, the modern city centre is subsiding dramatically.
- Flooding also has grave financial consequences, as seen for example in the year 2007, when a good one-third of Jakarta’s area was inundated after severe rainfalls. Around 300,000 people lost their homes. The damage to infrastructure and buildings amounted to the equivalent of some 860 million US dollars.
Floods affect not just the city itself but also, indirectly, its surroundings – the city of Jakarta is part of an urban conurbation, also comprising the adjacent cities of Bogor, Depok, Tangerang and Bekasi. This is one of the largest agglomerations in the world, reflected in the name it is commonly known by today: the acronym “Jabodetabek”. Every year around 250,000 people move into this agglomeration, which means that about 35 million people will be living there in the year 2020.
Every time that Jakarta is flooded, it causes transport chaos in the neighbouring areas. And another issue affects the region as a whole: if diseases or epidemics break out in the flooded areas because of the standing dirty water, these can rapidly spread throughout the whole of Jabodetabek.
A giant bird to defend JakartaIn order to defend the city of Jakarta from greater floods in future, the Indonesian authorities are currently planning to create hydraulically filled islands that will shut off the approximately 35-kilometre wide Bay of Jakarta and be developed with residential, office and hotel complexes. The largest island alone is 10 kilometres long and will be given the form of a garuda bird with wings spread wide, the emblem of Indonesia. But resistance is stirring within the population. Wastewater could collect in the artificial lagoon landscape because there will barely be anywhere for it to flow into the open sea. Diseases could spread. The small-scale fishers fear losing their livelihoods because in future they will have to travel many kilometres further offshore in order to reach fishing grounds. But that is not possible, argue the fishers, since they only possess simple boats which are often in poor condition and not suitable for longer trips out to sea.
- 2.33 > As a defence against flooding, there are plans to create artificial islands off the coast of Jakarta by hydraulic filling. The largest island will be 10 kilometres long and shaped like Indonesia’s emblematic bird. But the project is controversial. It is feared that wastewater could accumulate in the artificial lagoon, ruining the livelihoods of fishers.
- Construction projects on land which are planned in the course of the hydraulic filling are another major source of potential conflict. The intention is to construct new office, business and residential quarters along the shoreline. In the interim, residents who previously lived in simple shacks and houses in this area are being resettled. Although they are obtaining cheap living space in high-rise buildings in other districts of Jakarta, how can they possibly be compensated for the impending loss of their culture and identity? If the fishers are resettled inland, closer to industrial plants and factories, they can hardly continue in their traditional occupation: fishers will turn into factory workers. >