Coastal Environments - CaseStudy Flashcards
Kiribati
LEDC Coastline under Threat
Kiribati and the Atolls
Kiribati is a collection of 33 coral atolls and reefs islands scattered across a swath of the Pacific Ocean. It has a population of 100,000, half of which live on the capital atoll of Tarawa. Much of Kiribati lies no higher than six feet above sea level. The latest climate models predict that the world’s ocean could rise five to six feet by 2100. The prospects of rising seas and intensifying storms “threaten the very existence and livelihoods of large segments of the population,” the government told the United Nations in a report in 2018. Half of the 6,500 person village of Bikenibeu, for instance, could be inundated by 2050 by sea-level rises and storm surges (know locally as King tide events, Spring Tide + Low pressure storm event), according to a World Bank study.
Sea Level Rise in Kiribati
~Physical Environment~
More Frequent and Extreme Coastal Flooding
On average, it is estimated that Kiribati has experienced an average sea level rise of around 3.7 mm since 1992 (this is hard to estimate given that El Niño years can produce temporary sea level rises). However, it is the extreme events that accompany climate change and sea level rise that currently are impacting Kiribati. For example, in 1997 Kiritimati island was devastated by an El Niño event that brought heavy rainfall and flooding, resulting in a half-metre rise in sea level. Roughly 40% of the island’s coral died and their 14 million birds left the island. The king tide’ event that inundated Kiribati in 2005 produced a storm surge of 2.87 m, which destroyed some villages, swept crops out to sea and contaminated water supplies.
March 2015 Kiribati experienced flooding and destruction of sea walls and coastal infrastructure as the result of Cyclone Pam, a category 5 cyclone that devastated Vanuatu. Kiribati remains exposed to the risk that cyclones can strip the low-lying islands of their vegetation and soil
Contamination of French Groundwater
The islands consist mostly of coral limestones. These rocks are porous and allow sea water to infiltrate easily. This means that the salt water table rises and falls with each tide - but also is rising incrementally as sea levels rise. The main consequence of this is the contamination of many of the island’s wells. The overall volume of groundwater in South Tarawa is dependent on the size of land area of the island. As this shrinks, so the volume of fresh groundwater is reduced.
The coral limestone is porous and allows sea water to flow through it. The saltwater table oscillates on a daily basis with the tides, and in the long term with the mean sea level. As sea levels have risen, many wells have become contaminated with salt water and can no longer be used.
Loss of Land
Some of the smaller islands of Kiribati have already been lost to sea level rise. Two small uninhabited Kiribati islets, Tebua Tarawa and Abanuea, disappeared underwater in 1999.
The islands of Kiribati are coral atolls. Coral can respond to sea level rise - if it is gradual enough, the coral pulyp can raise the atolls up as sea level rises.
In fact, there is some evidence of expansion on land in some of the islands of Kiribati. A study by scientists from New Zealand found that three of the main urbanised islands - Betio, Bairiki and Nanikai - increased by 36 hectares, 6 hectares and 0.8 hectares respectively due to the growth of new coral.
However, it stressed that the study examined area only and not vertical growth of the islands, and it concludes that the vulnerability of islands remains high and that even these new corals would be vulnerable to sea level rise and inundation. Also, if sea level rises at a rate faster than coral growth (and if the coral is damaged by ocean acidification, another consequence of global increases in carbon dioxidel, then the islands continue to be at risk.
~Human Environment~
Economic Coasts
Unless significant adaptation measures are introduced, Kiribati’s capital of Tarawa, home to half the country’s population, will be 25-54% inundated in the south and 55-80% in the north by mid-century, and the country’s one airstrip in the south of the island will be eroded. The causeway roads that link the various parts of Tarawa together are being eroded by rising seas. If damaged, this could disrupt socioeconomic links, making it difficult for inhabitants to access services including the island’s hospital.
For a country with an annual GDP of only $600,000, the cost of the adaptation measures needed for all inhabited islands is estimated to be around $2 billion.
Food Security Problems
Coconut is the main cash crop for about 55% of the population. But it and other crops such as breadfruit and giant taro are susceptible to saltwater intrusion due to storm surges and overwash. On the island of Abaiang. the freshwater milkfish that provided protein to the local people are now totally gone. The taro plant, which is grown in groundwater pits 200m from the coast, is threatened due to saltwater contamination of the groundwater supplies. In 2013. the government of Kiribati purchased 20 km? of land on Vanua Levu, one of the Fiji islands, around 2,000 km away. It bought the land from the Church of England for around $9 million.
The land is currently being used for farming and fishing to try to guarantee the nation’s future food security.
Relocation of Villages within Kiribati
The populations of many of the villages closest to the sea in the islands have had to relocate. For instance, the village of Tebunginako on the island of Abaiang has already been badly affected by rising seas.
Over the past 40 years, sea level rise and storm surges have caused major issues for the inhabitants of Tebunginako. Groundwater began to become contaminated in the 1970s. The loss of land became so great that the village had to be relocated on the island. Now, the remains of thatched huts and the village hall sit around 30m offshore. Around 2005, the village was relocated about 50m from the then position of the shore. However, now at high tide, some of the houses, the Catholic church and village hall are surrounded by a moat of saltwater as the sea flows in and floods what was formerly a freshwater pond.
On the main island of Tarawa, 40 homes in the village of Te Bikenikoora have had to be relocated up to 2013 and the meeting house was only saved from a king tide in 2013 by the actions of all the villagers.
Summary
• Sea levels can change due to eustatic and isostatic causes. Eustatic changes are global changes in sea level associated with glacial and interglacial periods. Isostatic changes are local or regional changes in sea level resulting from glacial and tectonic causes.
• These sea level changes produce associated landforms. Emergent landforms include raised beaches and relict landforms. Submergent features include rias and fjords.
•Rising sea levels associated with climate change threaten the physical environment and the human environment, as can be seen in the case study of Kiribati.
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