Regional Climate Variability
Impact on water resources
Left-Right: Constrained water flow in the Padma. Gangotri glacier melt
The water regime of South Asia is of regional character and the water crisis should be solved regionally using collective efforts under SAARC forum. SAARC Meteorological Research Centre (SMRC) which is situated in Dhaka can play its due role in this respect. Water is an essential element for pursuing the basic functions of livelihood and sustainable economic growth. In South Asia, monsoon rainfall and snowfall over the Himalayan mountains constitute critical resource for the region's large economy and livelihood. In some areas, 10-20% of total water budget comes from the snow and glacier melts over the Himalayas. The big rivers of the region the Ganges and Brahmaputra originate in the Himalayan reservoirs with huge deposit of snows and glaciers (Gangotri and the Kailas-Manasarowar regions respectively). Being fed by the rain and snow-glacier melt water, these rivers flow over vast flood plains and traverse thousands of kilometers and cross the territory of Bangladesh before falling into the Bay of Bengal. Moreover there are innumerable small rivers, canals, lakes and beels (swamp water body) which act as valuable water resources. The river Meghna is one of the important drainage systems of Bangladesh which originates by convergence of a number of rivers flowing from the Shilong Plateau situated in India to the northeast of Bangladesh. The South Asian region is strongly dominated by the southwest monsoon activity. It experiences unimodal seasonal distribution of rainfall with principal amount of its rainfall (more than 70% in case of Bangladesh) belonging to the monsoon season (June-September). The pre-monsoon season (March-May) also produce good amount of rainfall (around 19% of the annual in Bangladesh). The winter is dry. The available surface water is not adequate for growing crops especially in the winter (December-February) and in the relatively dry part of the pre-monsoon months; these are the water deficit period of the annual hydrological cycle. It is to be noted that the consumption of water is gradually rising in the region with time due to increasing population, parallel increase of crop production and accelerated growth in economic and social sectors the total water resources remaining more or less constant. For the lower riparian countries like Bangladesh, the surface water deficit in the dry season has become very acute during the recent decades. The withdrawal of water from some of the transboundary rivers in the upstream aggravates this situation and severely affects the flow conditions within Bangladesh impacting severely on the environment and ecology of vast areas of the country. The best example is the river Ganges, the flow of which prior to entering Bangladesh is intervened at Farakka point. Though there exists an agreement between India and Bangladesh for water sharing but it is not of much help as the quantity of water reaching Farakka in the dry period is not so high to sufficiently augment the flow of Padma after sharing. The distributaries of Padma, which drain down over southern Bangladesh and fall to the Bay of Bengal crisscrossing the Sundarbans and adjacent areas, remain almost dry in the lean period. As a result the salinity front gradually moves to the north degrading the land quality of vast areas including the ecology and environment of the Sundarbans due to contamination with high salinity. Moreover, the surface water irrigation practices over the flood plains of Padma have been seriously affected, because of which the ground water has been exploited for rice cultivation to overcome the food crisis of ever increasing population. It has been evident that the ground water level is declining due to its overexploitation i.e., the rate of withdrawal is higher than the normal rate of recharging during the monsoon season. Above is the situation of the country's water resources; the global warming and associated climate change would exacerbate the environmental degradation and severely impact on various sectors such as water resources, agriculture, human health, coastal and other natural resources, etc. The frequency and severity of the weather related natural disasters are also increasing all over the world including Bangladesh. According to IPCC (2007) report, the warming of about 0.76 0C has taken place over the whole earth during the period of about one century. The warming rate has been accelerated in the recent decades. The general circulation models have predicted that the global temperature would increase due to enhanced greenhouse gas by about 1.5-5.80C by the end of the 21st century. The studies have shown that the temperature have increased also over the region including Bangladesh. It has been reported that the average temperature of Nepal shows increasing trend of 0.0235 0C /year during the period 1966-2003. The stations situated in higher altitudes of the Himalayas have stronger increasing trends. The increased temperature is supposed to enhance the evaporation and evapo-transpiration which would further aggravate the water stress. Most terrifying impact of warming that has been observed over the Himalayas is the overwhelming evidence of shrinking of the glaciers. The cause of such retreat of glaciers is the enhanced melting of the glaciers due to the increase of temperature possibly with concurrent lowering of the precipitation. The melting of the glaciers causes decrease in the Albedo (the reflecting power of solar radiation by the surface) of the areas resulting in higher absorption of solar energy providing feedback effect for further accelerating the warming rate and glacier melting process. Accelerated glacial melt questions the very perennial nature of many of the Himalayan flowing rivers. By 2050, the annual runoff in the Brahmaputra is projected to decline by 14% (IPCC 2001), which will have tremendous downstream consequences. Increased warming might result in increased flow initially with reduced flow later as the glacier disappears. Available records suggest that Gangotri glacier is retreating by about 30 m per year. Thus the increased population pressure, enhanced economic development, intensive agriculture and upstream intervention of the river flow being associated with water stress due to warming of the air and shrinking of the Himalayan glaciers will cause severe impacts on environment, ecology, agriculture, human health, economic development and livelihood of the people of Bangladesh. The sea level rise, loss of coastal lands due to northward extension of the tidal inundation due to sea level rise, increased salinity in the southern Bangladesh and enhanced weather related disasters add new dimensions to the problems. Poverty is a negative factor resisting the resilience towards the coping of the multidimensional impacts. Now the major task before the nation is to analyze the details of the climate change, its variability and impacts on all sectors and for all the vulnerable areas of the country. This primary task is highly scientific in nature and requires multidisciplinary team work of climatologists, scientists, engineers and other relevant experts. We particularly concentrate on the adaptation measures against the dry season water crisis. One of the national solutions would be to preserve the rain water and runoff flowing along the rivers using multipurpose dams within the country. However, more feasible as well as fruitful long term solution would be the construction of dams over the upstream. Studies in Nepal have identified 28 potential reservoir sites, 9 of which are classified as large, each having large storage capacity of over three billion cubic meters. From the Bangladesh perspective, the storage project in Nepal that has the maximum potential for augmenting the flows at Farakka is the Sapta Kosi High Dam Project. This potential reservoir envisages a live storage of about nine billion cubic meters, and the stored water behind the High Dam could augment the lean season Ganges flows and benefit both India and Bangladesh. It must be repeated here that storage reservoirs in the Himalayas would have to be multipurpose in order to be economically justifiable. These reservoirs may be used for fisheries and clean energy generation in the form of hydroelectricity in addition to water supply to rivers and canals and for other uses. The water regime of South Asia is of regional character and the water crisis should be solved regionally using collective efforts under SAARC forum. SAARC Meteorological Research Centre (SMRC) which is situated in Dhaka can play its due role in this respect. Early Warning of Natural Disasters and Management in the context of climate change is also an important issue for the regional consideration. At the end, I would like to stress on the development of expert manpower in the field of climate, weather, water and ocean. Though Bangladesh is a disaster prone country, its manpower development in the relevant fields has not yet got required attention. The expert manpower will be able to efficiently handle the problems.
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