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You are here: Home » Impacts of G. Warming » Sea Level Rise » Bangladesh floods  » Ecosystem» Climate Extremes »  Droughts » Hurricane »Methane Clathrate » Ice Caps » Arctic Passage » Crop Security » Water Security » Soil Security
                                                                                                                

             Global Warming Causes Sea-Level Rise And Flooding


Global warming due to anthropogenic greenhouse gas emissions has caused sea level rise. Satellite observations show that since 1990s, sea level has been rising at an annual rate of 3 mm. Sea level is projected to rise at 1.7mm per year in the 20th century, and even faster in the 21st century. IPCC reported rise of 1.2 mm per year between 1993 - 2003, 10 - 20 cm by 2030 and about up to 1 m by the end of the next century. To people living in the low lying areas, vulnerability is increased by the likelihood of storm surges either due to more intense tropical cyclones or mid latitude storms and by other problems such as land subsidence, and the increased intrusion of salt into groundwater.

Changes in mean temperatures and rainfall, and rising sea levels will weaken the stability of land and soil structure, affect the suitability of land for different types of crops and pasture, the health and productivity of forests. Frequent and more intense rainfalls increase the incidences of pests and diseases, floods and mudslides, death casualties and population displacements. They affect biodiversity and ecosystems; cause economic loss, raise socio economic and resource insecurities.

 

Sea-level rises due to 4 factors:

 - Glacial melting,
 - Higher sea temperature,
 - Higher evaporation rates from sea
   and land
 - Heavier rainfalls

Figure shows the mean sea level rise
and future projections
Climate Change 2007 - IPCC

1. Glacial melting
Global warming has increased the melting of ice and glaciers in Arctic sea ice, freshwater ice, ice shelves, the Greenland ice sheet, Alpine and Antarctic Peninsula glaciers and ice caps, snow cover and permafrost.

 

2. Higher sea temperature
According to researches at the National Center for Atmospheric Research, even if no more greenhouse gases are added to the atmosphere, global sea-level will rise by four inches over the next century due simply to oceanic thermal expansion, an effect of global warming.

3. Higher evaporation rates from sea/land

Research indicates that global warming
also raises atmospheric and sea temperatures and accelerate water evaporation. This often results in an unbalanced distribution of global rainfall and thus may bring more dry spells and floods, simultaneously in different parts of the world. In China, the frequent drought in the north and floods in the south over recent years reinforce this conclusion.

Quote one of the many such examples :In Feb 2009, Eastern Australia faced two extreme weather conditions simultaneously.

 
 

4. Heavier rainfalls
The higher temperature increases the water vapor retention power in the air, resulting in higher intensity when precipitations do finally occur. It thus increases the frequency and severity of droughts....Read more

According to IPCC report, global sea level rose by about 120 m during the several millennia that followed the end of the last ice age (about 21 000 years ago), stabilized between
2000 - 3 000 years ago. Evidence showed that sea level started to rise from late 19th century.

 

Sea level rise has caused more frequent and severe coastal flooding
resulting in loss of coastlines, coastal lands, wetlands and mangroves. The increased severity in floods is projected to bring serious impacts to low-lying areas with high population density. Severe flood may cause large scale population displacement; resulting in socio economic instability and resource insecurity.  

In the mega deltas such as Kolkata, Dhaka and Shanghai that are undergoing rapid urbanization. Millions of people will be badly affected in terms of destruction of lives, properties, crops, livelihood means and infrastructures, incurring huge economic losses.

Shanghai, a rapidly urbanized city in the mega delta, has reported a sea level rise of 120 millimeters since 1977 - a level higher than the national average of 90mm, and fastest in history. Many scientists believe rising sea levels are caused by global warming but the city's continuous land subsidence exacerbates the problem. At the same time, the city is sinking by about seven millimeters every year, partly due to the overuse of underground water and the rapid urban construction. (Shanghai Daily Dec 4, 2007)
 











Handrails on the bank of Xiangjiang River are submerged by flood water in Changsha, capital of central China's Hunan Province

 

China is recently very much affected by this rise of sea-water level mainly aggravated by heavy rainfall. In East China's Fujian province, rains lasted more than 10 consecutive days. In Southwest China's Yunnan province, a torrential rain lasted seven-hours. In Guangdong province's Huilai county, 603.5 mm of rain fell over a six-hour period, setting a record in about half a millennium. These had caused the collapse of reservoirs and rivers banks, landslides, power failures, and damage to highways. (Many of the same areas until several months ago had endured the worst drought in a century.) The Xinhua Press reported that, as at June the floods in China in year 2010 have affected 70 million people in 22 regions with death toll of 379 and 141 missing. 4.45 million hectares of farmland had been inundated, causing direct economic losses of USD 17 billion.

 







A man climbs a ladder to reach a drainage sluice station in South China's Guangdong Province June 10, 2007. It was the worst flood to threaten 15 towns of the county in 50 years. [Xinhua News Jun
2007]


 

  Bangladesh has been plagued by floods throughout history. Major flooding recorded in recent years occurred in: 1987, 1988, and 1998; the most devastating one occurred in November 2007.

Cyclone Sidr hit Bangladesh on November 15, 2007 causing  massive destruction and extensive live loss in coastal communities

Cyclone Sidr hit Bangladesh on November 15, 2007, causing widespread flooding and massive destruction in coastal communities, with the Red Crescent Society estimating 10,000 of death toll. International groups pledged US$95 million to repair the damage. The flooding has been declared a national calamity by the government.

''Floods in Bangladesh can't be controlled even with all the resources of the world put together,'' President Ershad told the press. ''Even partial protection requires a lot of money, and Bangladesh is a poor country.''

 

Contrasting a poverty stricken Bangladesh, we now turn to the Netherlands, a developed industrialized country, more than half of which consists of coastal lowlands below sea level. It is one of the most densely populated areas in the world; with more than 55% of the 14 million inhabitants found along coastal mega cities such as Rotterdam, the Hague and Amsterdam. The Dutch are increasingly worried about the threat of rising sea levels with the advent of global warming.

 

The Netherlands has over the years established an elaborate system comprising about 400 km of dykes and coastal dunes to protect it from the sea. Further reinforcement would only require use of the effects of various forces (tides, currents, waves, wind and gravity) on the sands and sediments so as to create a stable barrier. No new technology will be required against sea level rise till the next century.
(Pic: Dykes of the Netherlands
 A. van der Linde - Wikimedia)

Dykes and sand dunes will just need to be raised; though additional pumping will be necessary to combat the intrusion of saline water into freshwater aquifers. The Dutch water-engineers also created inflatable rubber dykes placed near Ramspol. The dyes
will inflate during stormy times to prevent flooding.











The Red Light District of Amsterdam along water canals

 


An estimate of about USD 12 billion would be required for protection against a sea level rise of 1 m, which is probably within the reach of the country. In December, 2008, the Dutch Government unveiled a plan worth more than 100 billion euros over the next century. Part of this fund will be channeled into improving the country’s sea defenses, the like of adding huge sand deposit to the coast, and to improve drainage.

 

The Three Gorges Dam on Yangtze River in China helped to buffer the worst floods in decades in July 2010. The Dam was built primarily for power generation and flood control. In 2010, China experienced frequent incidences of torrential rains across the country. Usually heavy

rains had caused extensive flooding, numerous lives, damaged houses and buildings, reduced crop outputs, displaced millions of people and resulted in USD billions of
economic losses. The Three Gorges Dam helped alleviate what might have been a worse repeat of the
1998 flood which killed 4150 people in China. It helped to  as it blocked more than 40% of upstream water from the swollen Yangtze River.

 

(Pic shows the sluicing of flood waters at the Three Gorges Dam in Yichang, central China's Hubei Province, July 19, 2010)

 

The poorer and smaller islands are also most exposed to multiple risks which threaten islanders'  livelihood. Risks are coastal erosion, coral bleaching, and reduction in fresh water resources. The rising sea water causes intrusion of salt water into fresh water resources, aggravating the existing water-stress problems. Examples are the Maldives in the Indian Ocean, consisting of 1190 individual islands, and the Marshall Islands in the Pacific, which lie almost entirely within 3 m of sea level.

In the US, rare and deadly flash flooding events are not uncommon, with recent (mid 2010) line-ups of extreme precipitation in Arkansas, Tennessee and Oklahoma. The rainfall was extremely unusual, as most of it fell in just a few hours. The Tennessee event, in which 13 -19 inches of rain fell during a two-day period, flooding much of the state including downtown Nashville, was around a 1-in-1,000-year event. And the Oklahoma City floods were a 1-in-100-year event.

In Brazil, in its capital of Rio de Janeiro, a record 11.3 inches rain fell within 24 hours in mid April 2010, causing severe flooding, and mudslides. Thousands of people have been left homeless, with reports of at least 154 deaths and many missing. Two months later, in late June, heavy rainfall resulted in severe flooding and mudslides in Alagoas and Pernambuco states.

 

Several rivers reached record levels, sweeping away bridges, roads, hospitals and schools. Entire towns and villages were swept away as rivers banks burst. More than 150,000 people were left homeless, and death toll climbed to 57.

Brazil flood June 2010. People travel by boat in a flooded street in Trizidela do Vale

 

Many scientists warned that the IPCC probably made a far too conservative estimate of sea level rise of 1.7mm per year in the 20th century when it explicitly left out the ice effect. With the earlier than anticipated melting of ice and the shrinking of ice sheets, scientists warned of far greater and much earlier rise of sea level ahead.

The Environment Agency said 2,000 properties between Kingsdown and Pegwell Bay were at risk from flooding.

Figure could rise to 6,000 by 2017 due to climate change and rising sea levels.

Pic: Erosion has affected St Margaret's Bay in Dover in recent years. (BBC Aug 2007)

 

Alarmingly, these extreme events are becoming more common, with high probabilities of increased frequency and severity in decades to come, as more water vapor is added to the atmosphere in response to a warming climate.
 

 
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