INTRODUCTION
Bangladesh is one of the poorest and most densely populated countries in the world. The poor are particularly dependent upon safe & reliable water resources for their health and livelihoods.  There are considerable regional and seasonal variations in water-livelihoods relationships: Monsoon rainfall, river discharge fluctuations, groundwater availability, saline intrusion, fish availability and others (differing by region).  As a result, rural communities, and especially the poor, in all parts of Bangladesh are severely affected by climate variability.  Flood damage has been particularly extreme the last 15 years, 1992 and 1998 being the worst in living memory.  Floods are among the most costly natural disasters in terms of human suffering and economic losses in Bangladesh.  Approximately 20 percent of the country experiences normal annual flooding and all the previous major flooding events have inundated more than fifty percent of the country’s total area. Conversely, low rainfall years, such as 1997 and 2001, also have very serious implications for agricultural productivity, fish availability, and other aspects of rural livelihoods.

CLIMATE CHANGE
The United Nations Framework Convention on Climate Change (UNFCCC) defines climate change as, “a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods”.

CLIMATE CHANGE & BANGLADESH
Rapid global warming has caused fundamental changes to our climate. No country and people know this better than Bangladesh, where millions of people are already suffering. Sudden, severe and catastrophic floods have    intensified and taking place more frequently owing to increased rainfall in the monsoon. Over the last ten years, Bangladesh has been ravaged by floods of catastrophic proportion in 1998, 2004 and 2007. Heavy downpour over short spell has resulted in landslides. Cold spell claims human lives as well as damage crops. Droughts often affect even coastal districts. Bad weather keeps the coastal waters risky for fishing expeditions. Damages and losses due to climatic extremes like floods, cyclones, tornados, and droughts are phenomenal to the victims as well as the state.  These are early signs of global warming effects. Sea level rise in the coming decades will create over 25 million climate refugees.
The low lying topography, riverine and coastal flooding, tropical cyclones, storm surges, tornadoes, widespread poverty, higher population density, poor institutional development etc. have made Bangladesh more vulnerable to climate change and variability. Climate change is likely to have several important impacts on Bangladesh. The main threats of climate change to Bangladesh are increased flooding, drainage congestion, decrease of fresh water availability, disturbance of morphological processes, salinity intrusion, frequent cyclone and storm surge flooding. The climate change risks in water sector would bring great challenges in water resource management in Bangladesh.

THE IMPACT OF CLIMATE CHANGE ON CRITICAL AREAS
The effects of minor levels of climate change are already being felt, with impacts across many economic sectors. While there will clearly be some gains from climate change (for example, agriculture in some northern regions should increase in productivity due to a rise in temperatures), most of the impacts will be negative, and gains and losses will not be evenly distributed. For example:

*  Water resources
*  Coastal resources
*   Ecosystems
*   Human health
*   Agriculture

IMPACT OF CLIMATE CHANGE ON WATER RESOURCE IN BANGLADESH
Water related impacts of climate change will likely be the most critical for Bangladesh – largely related to coastal and riverine flooding, but also enhanced possibility of winter (dry season) drought in certain areas. The effects of increased flooding resulting from climate change will be the greatest problem faced by Bangladesh. Both coastal flooding (from sea and river water), and inland flooding (river/rain water) are expected to increase. 

Flooding in Bangladesh is a regular feature and has numerous adverse effects, including loss of life through drowning, increased prevalence of disease, and destruction of property. This is because much of the Bangladesh is located on a floodplain of three major rivers and their numerous tributaries.

One-fifth of the country is flooded every year, and in extreme years, two-thirds of the country can be inundated (Mirza, 2002). This vulnerability to flooding is exacerbated by the fact that Bangladesh is also a low-lying deltaic nation exposed to storm surges from the Bay of Bengal

There has been a trend in recent decades of much higher inter-annual variation in area flooded. 

Since the late 1970s flooding events have tended to cover significantly lower or significantly higher areas than what was observed in prior decades. This trend in extremes cannot be simply attributed to climate change. Rather several other factors are at play. First, better flood monitoring and control measures have probably contributed to significant reduction in areal coverage of moderate flooding events, which now cover much lower area.

With regard to extremes at the upper end such as the 1988 and 1998 flooding events, climatic variability (including events such as the El Nino Southern Oscillation) as well as long term climatic change could certainly be contributing factors. Looking into the future, climate change is likely to exacerbate flooding for a number of reasons, including the following:

INCREASED GLACIER MELT
Higher temperatures will result in more glacial melt, increasing runoff from the neighboring Himalayas into the Ganges and Brahmaputra rivers. Given the altitude of the mountains and the enormous size of the glaciers, this problem will most likely continue over the century. The problem could be of even greater concern as there is evidence to show that temperatures in the Himalayas (where the glaciers are located) are rising at higher rates, thereby contributing to enhanced snow melt.

INCREASED PRECIPITATION
While this is not certain, the climate models tend to show increased precipitation, particularly during the monsoon season. This will contribute to increased runoff. For example, Mirza and Dixit (1997) found that a 2°C warming with a 10% increase in precipitation (close to the mean GCM projection for 2100 June-July- August) would increase runoff in the Ganges, Brahmaputra, and Meghna rivers by 19%, 13%, and 11%, respectively.

SEA LEVEL RISE
Sea level rise will result in coastal flooding both under ambient conditions (given the low elevations of the coast), and even more so in the event of storm surges. It will also indirectly cause riverine flooding by causing more backing up of the Ganges-Brahmaputra-Meghna rivers along the delta.

INCREASED INTENSITY OF CYCLONE WINDS AND PRECIPITATION
As discussed in Section 3.2.2, IPCC concludes that there is evidence of a 5-10% increase in intensity (wind-speed) that would contribute to enhanced storm surges and coastal flooding. IPCC also projects a 20-20% increase in intensity of associated precipitation that would contribute to (rain-water) flooding both in the coast and inland as the cyclone makes landfall. These estimates however are for tropical cyclones in general and are not location specific. Assuming a positive correlation between sea surface temperature and tropical cyclone intensity, Ali (1996) calculated the effect of a repeat of the 1991 cyclone with a 2°C increase (which causes a 10% increase in wind speed) and a 0.3 m sea level rise. He estimated that this would result in a 1.5 m higher storm surge that would inundate 20% more land than the storm surge from the 1991 cyclone.  

On the other hand, it is also possible – though considerably more uncertain - that drought could increase under climate change. Drought is a recurring problem in Bangladesh: 19 occurred between 1960 and 1991. Drought is typically caused when the monsoon rains, which normally produce 80% of Bangladesh’s annual precipitation, are significantly reduced. The southwest and northwest regions of the country are most vulnerable to drought. The estimates from the climate models do not yield a clear picture of how droughts will change. The estimated changes in precipitation are not significant. The models tend to show increased monsoon precipitation and annual precipitation, which could mean fewer droughts. But, a number of climate models estimate decreased annual precipitation, and the models tend to show reduced precipitation in the winter months. So the possibility of increased drought cannot be ruled out.

Water-related adaptation to climate change: an overview

Table: Some adaptation options for water supply and demand
 

Supply-side

Demand-side

Prospecting and extraction of groundwater

Improvement of water-use efficiency by recycling water

Increasing storage capacity by building reservoirs and

dams

Reduction in water demand for irrigation by changing the cropping calendar, crop

mix, irrigation method, and area planted

Desalination of sea water

Reduction in water demand for irrigation by importing agricultural products, i.e.,

virtual water

Expansion of rain-water storage

Promotion of indigenous practices for sustainable water use

Removal of invasive non-native vegetation from riparian

areas

Expanded use of water markets to reallocate water to highly valued uses

Water transfer

Expanded use of economic incentives including metering and pricing to encourage

water conservation


Conclusion
Bangladesh is critically vulnerable to climate induced hazards, but the core elements of its vulnerability are primarily contextual. It is probably the only country in the world with most of its territory lying on the deltaic flood-plain of three major rivers and their numerous tributaries. Between thirty to seventy per cent of the country is normally flooded each year. We should use our water resource properly. As a result of climate change our water resource will face great trouble. So we have to adopt options for water supply and demand.

References
1.    DEVELOPMENT AND CLIMATE CHANGE IN BANGLADESH: FOCUS ON COASTAL FLOODING AND THE SUNDARBANS, by Shardul Agrawala, Tomoko Ota, Ahsan Uddin Ahmed,  Joel Smith and Maarten van Aalst.
2.    Climate change and water resources published by Water Aid.
3.    Global Climate Change and Water Resources in Bangladesh, by IVAN SARWAR, MEHEDI ALAM, SOFIA STEPANYUK, RIAZ SARWAR.