Our dry season water needs

Although the delta waterbodies, but they do not hold much water for dry season

The nation's water resources provide multitude of services to the population and to the environment as well. Although Bangladesh has not yet managed to plan to utilise the river water in large scale, but it is considered to be the largest source of water. Beside rivers, surface water (ponds, lakes, beels) is traditionally used and from the last two decades ground water is being used both for domestic and commercial purposes. Depending on the purpose, the demand of water supply can be categorised into a) domestic, industrial and commercial uses; b) irrigation demand; c) non-agricultural demand (fishery, forestry and environment); d) in-stream demand.

Domestic use of water mainly includes, drinking, bathing, cooking, washing etc. Per capita consumption varies according to the standard of living, mode of water supply, availability and quality of water, between urban and rural areas. According to the National Water Management Project (NWMP) estimation, average per capita consumption in metropolitan, town and rural areas is found to be 139 liters per day (I/d), 118.91/d and 101.51/d. but the figures seem to be unrealistic, particularly for the rural areas, because in rural areas pond water is usually used for domestic purposes other than drinking and cooking. Domestic use of ground water in rural areas is about 25 1/d per person. But with the increase in population and decrease in water availability, demands for water will gradually rise. As per projection of WARPO, within 2025 the population in the rural and urban areas will increase to 34 and 15 million and 27.5 and 28.5 million respectively. Thus, total demands of water for domestic purposes during dry season may be about 180 and 350 million cubic meters (Mm3) in 2025 and 146 and 665 Mm3 in 2050, in the rural and urban areas, respectively.

In commercial and industrial sectors, the use of water covers the area of washing, dilution, processing and manufacturing of products. Moreover, production of electricity in Bangladesh depends on the supply of river water. Therefore, commercial and industrial demands typically stands at 8-11% and 10-15% respectively, of the total water supply for piped distribution systems. Where as, WARPO adopted 10% and 15% of gross domestic demands in urban areas (metropolitan areas and towns) as gross commercial and industrial demands, respectively.

Irrigation is highly demanded for the production of crops. However, the extent of irrigation varies according to the type of crops, different phases of crop growth and obviously seasonal variation. According to previous studies, if non-irrigated crop is planted following an irrigated crop, then the requirement for irrigation would be minimal. Moreover, the demand of water varies depending on crop development stages: initial, growing, mid-season and late season. During the dry season (November-May), irrigation is provided with the aid of ground water, as the surface water becomes scarce and the upstream flow gets minimised. With the gradual reduction in upstream flow and late arrival of monsoon, the irrigable areas are increasing as well. According to NWMP, total irrigable area in the GDB delta is about 26,160 km2, with a gross irrigation demand of about 15,665 Mm3.

Non-agricultural demands arise from areas under fisheries, forestry and environmental importance. Areas under fisheries includes major and regional rivers, standing waterbodies (ponds, lakes), and seasonally flooded waterbodies (haor, baor, beels). These are the major fish habitats and breeding grounds, supporting the sustenance of the fish population of Bangladesh. Fishery is still one of the major economic sectors on which the livelihood of the poor fishermen depends. But the waterbodies are getting decreased due to the encroachment for agricultural activities, sedimentation and encroachment for human habitat. Other than anthropogenic reasons, under natural condition, water from these waterbodies are getting evaporated to the atmosphere and draining to the surrounding rivers. Therefore, to meet the demand of the total area under fisheries which is about 940km2, the estimation is about 435 Mm3.

Forestry sector demands a huge percentage of water, although the intake is not visible. A medium sized tree can absorb up to 30 ton of water from the ground water table and release it to the atmosphere through the process of photosynthesis. Therefore the quantity of water required to met evapotronspiration demands of such trees is a net demand and needs to be accounted for. Total demand from forestry sector was estimated to be about 810Mm3.

Environmental demand includes that for rivers and parks, playgrounds and roadside plantations in urban areas. For rivers the demand rises due to the evaporation loss to the atmosphere and leaching into the groundwater. The total area of rivers is about 960km2 and to meet the demand for water the estimation is about 430Mm3. And urban areas under environmental use, includes mainly parks, playgrounds and gardens and in case of the rural areas the use includes household trees, bamboo clumps, yards, etc. Total area under environmental uses (excluding rivers) was found to be about 5945 km2 from the district level data given in NWMP the break up into the urban, rural and other areas being 1883, 2829 and 1145 km2 respectively (WARPO), the total environmental demand was found to be about 150Mm3. Water is also required to control the salinity intrusion into the rivers. Inadequate discharge of upstream rivers, would let the saline water be pushed in by the Bay of Bengal. That may destruct the natural balance of the inland water ecology, including fishery, aquatic flora and fauna and navigation. To prevent saline water to be pushed in, approximately 700 million acre feet of water need to be flashed out per second by the GBM and their distributaries. More precisely, the in-stream flow requirement to push the salinity fronts in the rivers near Khulna and to prevent environmental degradation in the SW hydrological region was estimated to be about 150m3/s in the Gorai river and 25m3/s each in the Kobadak, Betna, Mukteswari and Hari rivers (WARPO).

However, the supply of water to meet the demand of different sectors does not remain at the same range. Though, the GBM and their distributaries flash out 953 million acres feet/second throughout the year, but the proportion of the flow becomes almost half during the dry season. The variation between average high and low flow is very distinct, which is about 1:4 in the monsoon and 1:20 during the dry season. The reduction in upstream flow during the dry season is mainly caused due to lack of rainfall and such reduction is believed to be enhanced because of the construction of Farakka barrage on the Ganges. During dry season as there is no rainfall, the surface gets dried up and the surface water (ponds, beel, haor, baor, etc) gets evaporated as well. In such circumstances, river water and ground water is the only source to be utilised for crop production and other water related activities. But as 90% of the river water flowing through Bangladesh is originated outside the country. Bangladesh fails to regulate the water flow whenever required.

Therefore, during dry season farmers are unable to produce crop without extensive irrigation. But recently, many existing irrigated areas are experiencing regular shortages during critical dry periods (11 March to 10 May). These shortages are causing farmers to grow low water demanding crops during earlier months of the dry season, and to keep the lands fallow for subsequent months when ground water is low. Consequently, in spite of technological support, the enhancement of crop production remains stagnant during dry season. Although measures have been adopted to provide irrigation, but it covers only about half of the potential area. All irrigable areas (75600km2) need to be brought under irrigation to meet increasing food demands for growing population, which now exceeds 140 million.

Furthermore, proper management practice needs to be adopted for irrigation. Because, though irrigation is supporting crop cultivation, on the contrary it is causing problem for pisciculture and navigation. Because the use of water in irrigation lessens the resource's utility for others downstream, it often leads to conflicts among different stakeholders. Farmers irrigate their lands by pumping water from the ponds, beels, haors, baors and small rivers. This leads to be disruption in fish culture. Therefore, the fishermen fail to harvest beneficial percentage of fish, which leads to conflict with the farmers. Such conflict can only be prevented through proper management of irrigation and water bodies during dry season.

Water scarcity during dry season is getting intense as a result of variations in the seasonal cycle caused by climate change. Excessive dryness of land, prolonged dry season, desertification of the northern region of the country are some of the symptoms indicating the change in the seasonal cycle. Prolonged dry season has become more frequent in recent years, with phenomenon as "Monga", leading to scarcity of food. Whatever the reason, water scarcity during dry season is imposing problem for the agriculture as well as the economy of the country and the vulnerable group are suffering the most. In spite of being a riverine country Bangladesh is failing to quench the thirst of the nation. Assessment for water availability during dry season is essential in such circumstance to calculate the quantity of water that can be abstracted and utilised, to meet the demand of all sectors.

Lamyea Bintea Ali is studying at IUB (SESM).