Climate change and sea-level rise (CCSLR) have a significant impact on world water resources which will exacerbate local to regional water crises, with serious implications for public health, environmental sustainability, food and energy security, and economic development [1].

One of the most critical impacts of CCSLR is a saltwater intrusion in surface water, groundwater, and soil [3, 3]. For Bangladesh, major concerns in the water sector are the rapid decline in shallow groundwater sources and widespread arsenic contamination, which lead to extraction from deep aquifers [4]. Salinization of soil and water, especially in freshwater aquifers has now become one of the critical coastal hazards in Bangladesh [5]. CC modeling projected future pathways with an increase in intensity and frequency of cyclone-storm surge events [6], there has been a high sea-level rise (SLR) prediction for Bangladesh even up to 1 m around 2100 that would affect 17.5% of total landmass [7]. Bangladesh is thus at critical risk in terms of its water resources management against a changing climate.

Salinity intrusion due to anthropogenic activity:

The Asian continent supports more than half of the world’s population with only 36% of the world’s water resources [8] and Bangladesh is one of the countries with heavy water withdrawal practices [9]. Compared to CC impact anthropogenic forcing is much more pronounced in Bangladesh for salinity intrusion.

Salinity intrusion in Bangladesh is very seasonal, minimum during the wet/ rainy season (June-September) and maximum in the dry season (March-May). The salinity intrusion problem was introduced with the initiation of the ‘Coastal Embankment Project' back in 1960 leading to change in natural flow processes. Sedimentation raised the riverbed led to drainage problems and saline water logging during high tides in many of the embanked areas- increasing salinity in water and soil simultaneously. The Ganges water treaty, commonly known as the Farakka treaty, which initiated the construction of the Farakka barrage upstream of the Ganges River, had a severe impact on the Bangladesh river network. The barrage started functioning in 1975, which resulted in a significant amount of reduced flow in Bangladesh during dry seasons and further propagation of saline waterfront inland. The impact of the Farakka project was long-lasting that permanently changed the soil, water, and environment regime in Bangladesh. Horizontal expansion of brackish water shrimp farming from the 1970s also made a severe impact on local soil and water, where saline river water was brought into embanked areas to fill up the large ponds used for shrimp farming. Since the 1980s, the Bangladesh agriculture sector bloomed - large areas were brought under rice cultivation with the help of irrigation projects in the coastal belt. That led to the depletion of freshwater in shallow aquifers and the propagation of seawater into the voids. Unplanned water management practices in the coastal areas such as the use of saline water in shrimp farming and the over-extraction of shallow GW accelerated the process of salinization in Bangladesh.

Anthropogenic interventions and activities is presently the primary cause of salinity propagation in coastal Bangladesh. However, the impact of gradual CCSLR and increase in extremes events are expected to be much more pronounced in future scenarios leading to large scale salinity intrusion in water and soil. . Thus, CCSLR coupled with anthropogenic activities pose a serious threat to future GW development and management along with public health complexity in Bangladesh.

Evidence of increased salinity in the coastal areas of Bangladesh:

There is increasing evidence of salinity increase in soil and water [10] however; the exact magnitude of the problem is yet to be fully explored. In 2009, it was estimated that the total saline area has increased to 1.05 million hectares from 0.833 hectares in only four decades timeframe [11]. The coastal area in Bangladesh constitutes 20% of the country of which about 53% are affected by different degrees of salinity. Salinity intrusion mechanism and impact study had always been a part of coastal GW studies and some major studies on the issue are the BWDB-UNDP study, DPHE-DANIDA study, IBRD study, and BADC study. Among the studies, the Bangladesh Agricultural Development Corporation (BADC) established an annual monitoring system to assess the GW salinity by installing 130 boreholes of 200 feet in different coastal districts, with the focus to monitor the irrigation water salinity status [12], which primarily extract water from shallow aquifer layer. All the studies reported salinity increase in GW aquifers but, research on domestic drinking water sources is quite minimal. Icddr,b has a couple of studies on the relation of drinking water salinity and potential health impacts where they tested the point sources i.e. tubewells in selected study areas. Under the ESPA Deltas study, the team in collaboration with IWFM, BUET had prepared a salinity map for the deep aquifers/ tubewells (depth > 500 feet) of the study area, stretched over from south-west to south-central part of Bangladesh (map 1).

The national standard for salinity in drinking water:

The WHO guideline value for drinking water salinity is 250 mg of Chloride per liter (mg/l) for Chloride (Cl) and 200 mg/l for Sodium (Na) which has been standardized based on taste threshold, not on health considerations. The value adopted by Bangladesh is 150-600mg/l; but for more practical reasons and in case of lack of non-availability of alternative sources, the standard is set to 1000 mg Chloride per liter for coastal areas [13] which already allows consumption of high sodium intake from water. Additionally, with a practice of high salt intake from food- the combined vulnerability of the coastal population to develop hypertension is quite high.

Water salinity monitoring and database:

Bangladesh Water Development Board (BWDB) initiated a study titled “Establishment of Monitoring Network and Mathematical Model Study to Assess Salinity Intrusion in Groundwater in the Coastal Area of Bangladesh due to Climate Change” in 2010; funded by the Climate Change Trustee Board under the Ministry of Environment, Forestry and Climate Change (MoEFCC). The BWDB (https://www.bwdb.gov.bd/en/ ) has then continued to routinely monitor different water quality parameters in coastal areas of Bangladesh.

Reference

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