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Mangroves Nature’s Defence Against Tsunamis


Nature’s Defence Against Tsunamis

Many Pakistani regions, such as Quetta, are located near fault lines that trigger earthquakes. One of such fault lines is the Makran Subduction Zone, located around 100 km southwest of Makran coast in the sea, where the Arabian and Eurasian tectonic plates meet. This is the place that could make Pakistan’s coastal cities and populations hit by a tsunami at any time. Since this fault line is from east to west, it runs along the coast of Balochistan to the coastal areas of Iran. It was due to this fault line that the Makran coast was hit by a tsunami on November 28, 1945, which caused huge financial losses as well as 4,000 deaths.
According to a research paper titled ‘The Potential of Tsunami Generation along Karachi and the Makran Coast of Pakistan’, published in Pakistan Journal of Meteorology, “Over 50 earthquakes of magnitude 8 and above have been reported in last 75 years along the coastline of Pakistan. Out of these, four were accompanied by tsunamis 1919, 1943, 1945 and 1956.” In addition, according to the research paper, sediments accumulated along the Indus River delta can also take a crucial part in tsunami, because an earthquake with even a weaker magnitude can trigger a submarine landslide in these sediments causing tsunami or effect of an earthquake-triggered tsunami can be amplified by the consequent submarine landslide in these sediments.
Similarly, there is another fault line, called Murray Ridge, located southwest of Karachi in the North Arabian Sea. It separates the Indus Basin from the Oman Basin. Although tsunamis caused by seismic activity and other factors can affect long-distance coasts, their effects can be very severe in nearby coastal areas. It is in this context that the United Nations has designated 5th of November as World Tsunami Awareness Day in order to promote awareness on how to prevent this natural disaster and minimize the damage caused by it.
Since a tsunami can reach coastal populations within minutes, the only way to save human lives from this catastrophe is to set up a functional early-warning system so that people and livestock may be evacuated before a tsunami hits. In addition, if you are in a coastal area and feel the tremors, the first thing that can affect you badly is a tsunami. Therefore, along with the early-warning system, you should also keep an eye on the signs around you. To mitigate the loss of life and property, a number of measures are taken around the world. One of those measures is forests, especially the coastal forests. These are commonly known as mangroves.
Owing to their natural setting, the mangrove forests provide natural protection to coasts. They act as a buffer zone between the sea and the human settlements. They are a powerful force to decrease the intensity of tidal surges, coastal floods and huge tsunami waves. They not only save coastal areas from sea erosion and landslides, but also strengthen the sand dunes on the beaches, making them a strong deterrence against huge sea waves. All these factors combine to make human populations safe and secure. The vitality of mangrove forests can be ascertained from experiments, conducted at Japan’s University of Kyoto, which established that a 100-meter-wide belt of dense mangrove forest can mitigate the destructive energy of a tsunami by up to 90%.
The significance and utility of mangrove forests have become more vividly evident since the December 2004 tsunami. According to a study conducted after that catastrophic event, only 7% of the villages of the Andaman Islands in the Indian Ocean – that had ancient forests – were affected by tsunami. In contrast, 80-100 percent of rural areas where there were hardly any mangrove forests were devastated. Investigations into minor tsunami events since 2004 have also concluded that the protection of mangrove forests, their restoration and afforestation as strategic green belts are some inevitable measures to protect human settlements against tsunami.
How mangrove forests do that?
Experts attribute this feature to the height of certain species of mangrove trees, the elasticity of their trunks, canopied branches, and the thin roots that extend far into the water, both in and outside. These trees stand as a flexible net against tsunami’s waves and absorb its force. It has been estimated that mangrove forests prevent more than $65 billion in property damages every year reduce the risk of flooding for 15 million people each year. In simple words, these provide the most cost-effective, nature-based solution as restoring mangroves is five times more cost effective than building ‘grey infrastructure’ such as flood walls or embankments, which also don’t help with climate change. Simply put they are one of the most efficient, cost effective Nature-based Solutions (NbS).
Moreover, the engineered grey structure does not prove highly efficacious and suffers wear and tear due to effects of climate change and hurricanes. Thus, it requires constant financial resources for its maintenance. On the other hand, the most valuable virtue of a natural marine defence, like mangroves, is that they re-grow even of self-harm. Studies by United Nations Environment Programme (UNEP) have established that every dollar invested in mangrove restoration provides a benefit of four dollars.
Mangrove vegetation is characteristically present in river estuaries and along the coast where the land meets the sea. They are a common sight on mudflats and banks of tropical and subtropical rivers and coastlines in many parts of the world. According to World Atlas of Mangroves, these forests are found in 123 countries. They are found only in deltas where the slit that has been washed away by the river water gets mixed with the seawater and is left on the shore. The seawater keeps constantly moistening it with its strong waves. In some places, seawater is always present at shallow depths. This is why these wetlands, located at the confluence of freshwater and brackish water, are covered with dense mangrove forests. According to the State of the World’s Mangroves 2021, “Overall, the total mangrove area was estimated to be 135,882km2 in 2016 – 11.96% of the world’s coastal area and 0.7% of the world’s forests.”
Pakistan is among the few lucky countries where this natural wealth exists in abundance. Mangrove forests are located in different parts of Pakistan’s 1050-km-long coastal strip of Sindh and Balochistan. Sindh’s 250 km long coastline is located in the southeastern part of the country between the Indus border along the Sir Creek on the east, and the Hub River along the Balochistan coast on the west. It can further be divided into two main parts: the Indus Delta/Creek and Karachi coast. Mangrove forests in Sindh, which are around 97% of Pakistan’s total mangrove forests, are found in delta areas from Rann of Kutch to Karachi. This region has been formed due to the amalgamation of the freshwater of the Indus and millions of tons of silt it brought along. In this region, there is a network of creeks that are 17 in number. They range from Sir Creek, which is contentious between Pakistan and India, to Korangi Creek near Karachi. The Indus River Delta, an important landmark of Pakistan, is spread over an area of around 0.6 million hectares. It comprises many large and small streams that are formed before the flow of the Indus into the Arabian Sea. It is a fan-shaped delta that includes rivers, mud flats, sand dunes, mangrove habitat, swamps and ocean bays. The Indus Delta, which is the sixth largest in the world, receives freshwater from the Indus River, which flows through the delta before falling into the Sea. Mangrove forests are divided into two main blocks here: Keti Bandar Block and Shah Bandar Block. Beyond the Shah Bandar Block in Thatta district is a narrow strip of Rann of Kutch that has many important wetlands.
The 800-km-long coastline of Balochistan stretches from the mouth of Hub River in the east to the Gulf of Gwadar (border with Iran) in the west. This coastline can also be divided into the coasts of Lasbela and Gwadar (districts of Balochistan province). There are several bays along the coast of Balochistan including Gwatar, Gwadar (West and East), Pasni and Sonmiani bays. The mixing of fresh river water with seawater on the Arabian Sea coast in Balochistan is dependent on seasonal rivers. However, there has never existed a permanent water supply system, like that of the Indus River, here and due to such a climate it is called “arid land”. The area covered by mangrove forests here much less than that in Sindh which is around 3% of the total area of Pakistan under mangrove forest. Mangroves are found on three places along the coast of Balochistan: Miani Hor, Kalmat Khor and Gwatar Bay (Jivani). Although the survival of Sindh’s mangrove forests is largely dependent on fresh river water, those of Balochistan are capable of withstanding the brackish water of the ocean. This is due to the disruption in the supply of river water and the development of their ability to adapt to seawater due to the natural evolutionary process.
The total area of mangrove forests in Pakistan has not been ascertained yet and different organizations have presented differing numbers. For example, in 1958, the dense mangrove forest area of 344846 hectares was transferred to the Sindh Forest Department. Then, we find in a 1966 document that the area of such forests is 344870 hectares. In 1985, the Sindh Forest Department declared this area to be 280,470 hectares. In 2003, SUPARCO stated that there were 86,728 hectares of mangrove forests on the country’s coastline, out of which 82669 hectares was on the coast of Sindh and 4058 hectares on Balochistan’s. Moreover, a book titled as “The Root Causes of Biodiversity Loss,” (London, 2000) puts this figure at 132,000 hectares, of which 129,000 hectares are on the Indus Delta and 3,000 on the coast of Balochistan. According to a 2005 joint study by SUPARCO and the Sindh Forest Department, there were 55,760 hectares of mangrove forests in the province. A 2005 report by International Union for Conservation of Nature (IUCN) suggests that mangrove forests in Sindh are spread over an area of 605,370 hectares. The WWF, in 2008-09, said that there were 98,128 hectares of mangrove forests in the country – 92412 on the Indus Delta and 1056 hectares along the coast of Karachi, as well as 4660 hectares on Balochistan’s Makran coast.
The Forest Resource Assessment of the Food and Agriculture Organization of the United Nations (FAO) reported an area of 95,000 hectares in 2015. In addition, according to Global Mangrove Watch, the area of mangrove forests in Pakistan was 64,157 hectares in 2016. According to the Sindh Forest Department’s website, the area of such forests is still 600,000 hectares in the province. According to a statement from the Chief Conservator of Forests, Mangroves and Rangelands Sindh, the area of these forests in the province was 107,000 hectares in 2009-10 which has increased to 220,000 hectares by 2020. In a statement issued on July 26, 2021, WWF Pakistan told about the presence of mangrove forests on an area of 130,000 hectares in the Indus Delta.
In spite of these varying figures, one thing is universally accepted that Pakistan is the biggest country in terms of area under arid-climate mangrove forests.
Historically, eight species of mangroves have been found in the Indus Delta. However, four of them have become extinct due to rising salinity levels. At present, Avicennia marina is the largest of four species of mangroves currently found in Sindh delta, having a share of around 90%. It is followed by Rhizophora mucronata with a percentage of 8%. The proportion of Aegiceras corniculatum is 1.5% and that of Ceriops tagal is 0.5%. There are three species of mangroves along the Makran coast. Of the four species mentioned above, only Ceriops tagal is not found in the coastal areas of Balochistan while the other three are found there. Miani Hor is the only area where these three types of mangroves are found.

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