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Of water, environment and flood control

Md.Asadullah Kuan
THE greenhouse effect leading to global wanning, first identified by the Swedish chemist Arrhenius in 1896, indicates that human activities like driving cars, burning coal, cutting trees and raising cattle have significantly increased the concentration of key greenhouse gases namely carbon dioxide, methane and nitrous oxide. This increase in greenhouse gases is thought to have enhanced the greenhouse effect that leads to global warming and consequent climate change.
Estimates drawn from reports by the Intergovernmental Panel on Climate Change (IPCC) project increase in average global temperatures ranging from 1.4 degrees to 5.8 degrees C by 2100 These numbers may seem small, but because average global temperatures are stable over long periods, this range represents a very significant rise in the earth's temperature over a very short period of time.
There has been an appreciable decrease in snow cover in the Northern Hemisphere and floating ice in the Arctic Ocean. Global sea levels have risen about 0.5m and precipitation over landfill has increased 0.1%. Experts say that the atmosphere has seen a 65% increase in carbon dioxide over the past few centuries. The seas around India have shown a 2.5mm rise per year oxer the past few decades. When ocean waters become warmer, they tend to expand. Add to this ice melts, and you have oceans rising.
Seas rising by millimeters and lands warming by fractions of degrees might not sound like much, but it is enough to change life forever. A half- metre sea rise, for instance, is enough to wipe out India and Bangladesh's coastal areas.
The impacts of such human induced climate change are wide and varied. The predictions of the scientists about many untoward happenings that were ruled out
earlier have come to be true. Polar ice caps have started melting causing sea levels to rise and swamping coastal communities. At the same time retreating glaciers in the Himalayas indicate that global warming has become a reality.
Increased incidence of storms accompa -nied by tidal surge due to higher rates of evaporation continues to devastate Bangladesh. This increased evaporation could also cause widespread drought and famine.
Impact on water and environment
Higher temperatures could hann the water quality of the rivers and lakes. In areas where river flows decrease, pollution concentration will rise. In order to keep pollution concentrations from increasing sewage treatment plants and other water pollution controlswill have to be upgraded.
The situation in cities like Dhaka, Narayanganj and Chittagong in respect of water hazards is appalling. Factories in these cities, as well as city dwellers, discharge harmful chemicals and toxic wastes into the Buriganga, Shitalakhya and Kamaphuli, while the farmers use agrochemicals and pesticides that not only pollute the river water but also wreak havoc on the eco-system.
Rivers in developed countries have become much cleaner over the last two decades. On the other hand, rivers in the poorest developing countries, like Bangladesh, by contrast have shown marked falls in levels of dissolved oxygen -- a key indicator of increased pollution by sewage To make things worse, supplies of fresh water that might dilute the sewage are dwindling in many areas because of drought, deforestation, and topsoil loss.
Water pollution is causing indisputable harms in poor countries. Because populations in poor countries are growing so fast that improvements in water supply have failed to keep pace with the growing number of people. T\vo billion people still have no access to clean water worldwide, and water contaminated by sewage is estimated to kill 3.4 million including two million children every year.
People now use 54% of the available fresh water and additional demand will further jeopardise all other ecosystems. That only indicates that water scarcity may soon limit economic development, particularly in China, India, Bangladesh and Pakistan.
Changing climate could also impair water quality by increasing the salinity of the water in the rivers, much of it caused by the absence of flexibility of the existing water management system. Rising sea level and reduced precipitation would increase the salinity of estuaries. Moreover, the decreased river flows could lead to excessive concentrations of minerals that run off from dams on various rivers.
Impact on flood control
Global climate change could also increase the frequency and severity of inland flooding. Bangladesh experienced the worst
ever flood of the century in the recent past. Flood studies in our country have never been linked to global warming, rather they relate to a focus on a shift in average conditions and assume that variability is otherwise unchanged.
As we could not envision the devastating floods of 1998 and 2004 we cannot also rule out the change in weather patterns in future that might bring about more calamities. Moreover, governments and concerned sectors in all countries that have large cultivable land, being fully aware of the cost and environmental impacts of flood protection structures, rely on land use regulation to prevent flood damages.
Dams once touted to be protection from floods often turn out to be one of the most troubling drawbacks. Traditionally, land near a river has been irrigated by floods and planted after they recede. A dam can stop this from happening and rob millions of people downstream of their livelihood.
Dam building has been cited as the most ill-thought out project. Other than cost factors, ecosystems were destroyed or permanently damaged. Moreover hydro-electric dams, once held as clean, renewable energy sources, turned out to be significant generators of greenhouse gases given off by the decomposing vegetation in tropical reservoirs.
More often than not, projects failed to deliver the benefits that proponents promised. For instance, some dams designed to reduce flooding actually worsened it. In hot dry areas salt build up in reservoirs has led to saline waters that ruined farmland. Dams, for all their material blessings, are responsible for some of the worst environmental tragedies in history.
Another catastrophic example ofdamm-ing rivers and streams is that it causes severe shortage of freshwater supply in the adjacent areas. Salt-water invasion has cost the economy rooted in fishing and agriculture because of huge sediment flow towards the mouths of the sluice gates, and in large areas by the side of the embankment that continues to expand.
In Bangladesh, we have abundant water resources with the big rivers still flowing in full fury in monsoon, but because of indiscriminate use of fertilisers and pesticides
and unplanned erection of dams, especially in the south western part of the country, water areas got polluted and water became unfit for human consumption. In ways direct or indirect playing God with water has had a tendency to bite us back.
As a solution to the water problem, "we must rethink water management" says Peter Gleick. one of the world's renowned experts on fresh water resources. We no longer live in a world in which rivers can be endlessly dammed, aquifers relentlessly pumped, ecosystems degraded and impoverished. At the same time, proposals that are coming to the fore include reducingwaste in irrigation, desalinating, recycling, making appropriate local choices of crops, employing low cost chlorination, and solar disinfectant techniques, increasing water harvesting from rain water sources for agricultural use and transportation of potable water to dry areas.
The planet is not actually running out of water, but its people are having an increasingly difficult time managing, allocating, and protecting the water that exists. In some areas, the hydrological cycle -- by which the fresh water of rain and snow eventually evaporates, condenses in clouds and falls again — may be taking longer time to complete as humans use water faster than nature can renew it.
Moreover, as much as the world becomes urbanised, its water crisis will deepen. Climate change causing freakish weather has only magnified the problem by polluting surface water sources through flooding and water logging. Saltwater invasion of the huge coastal areas wreaking havoc on the lives of 40 million people in the coastal areas of Bangladesh has cost the economy of the country dearly.
Dhaka has to rely largely on ground water, but aquifers take decades to recharge while the population growth in the city is exponential. As urban demands for water increase, supply of the developingworld's already water starved areaswill be further affected, creating an insurmountable food security crisis.
Md. Asadullah Khan Is a former teacher of physics and Controller of Examinations, BUET.
e-mail: aukhantxi@gmail.com