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Background: The global pandemic caused by SARS‐CoV‐2 has underlined the significance of strict genomic surveillance to track virus evolution and the possible emergence of new variants, particularly in densely populated countries like Bangladesh. This study outlines a strategic framework of genomic surveillance to track the evolution of the virus in Bangladesh between June 2021 and December 2022 through the National SARS‐CoV‐2 Variant Surveillance (NSVS) program involving collaboration across 4 major institutes and 13 hospitals nationwide. Methods: We aimed to capture the variants of SARS‐CoV‐2 throughout the country utilizing standardized procedures, modern sequencing technology, and stringent quality control, promoting data accuracy and the timely detection of new variants of concern. We sequenced over 2200 genomes, documenting the prevalence of the Delta variant initially, followed by the emergence of Omicron variants BA.1, BA.2, BA.5, and XBB, each affecting transmission rates and vaccine efficacy differently. Results: The clinical manifestations of the variants differed, with some symptoms occurring more frequently in Delta cases and vice versa. Vaccinated individuals were more affected by Omicron cases compared to Delta cases. These variants were responsible for two major COVID‐19 waves in the country, each with significant clinical effects. Phylogenetic analyses placed the local SARS‐CoV‐2 variants within a global context, indicating the Delta variant likely entered from India and Omicron from Europe. Conclusion: This research highlights the significance of collaborative surveillance strategies for guiding public health choices and the critical role of genomic analysis in monitoring virus evolution, shaping targeted pandemic responses. Bangladesh's contributions significantly enhance global insight into COVID‐19's genomic evolution. [ABSTRACT FROM AUTHOR]

Coasts and coastlines in many parts of the world are highly dynamic in nature, where large changes in the shoreline position can occur due to natural and anthropogenic influences. The prediction of future shoreline positions is of great importance in the better planning and management of coastal areas. With an aim to assess the different methods of prediction, this study investigates the performance of future shoreline position predictions by quantifying how prediction performance varies depending on the time depths of input historical shoreline data and the time horizons of predicted shorelines. Multi-temporal Landsat imagery, from 1988 to 2021, was used to quantify the rates of shoreline movement for different time period. Predictions using the simple extrapolation of the end point rate (EPR), linear regression rate (LRR), weighted linear regression rate (WLR), and the Kalman filter method were used to predict future shoreline positions. Root mean square error (RMSE) was used to assess prediction accuracies. For time depth, our results revealed that the higher the number of shorelines used in calculating and predicting shoreline change rates the better predictive performance was yielded. For the time horizon, prediction accuracies were substantially higher for the immediate future years (138 m/year) compared to the more distant future (152 m/year). Our results also demonstrated that the forecast performance varied temporally and spatially by time period and region. Though the study area is located in coastal Bangladesh, this study has the potential for forecasting applications to other deltas and vulnerable shorelines globally. [ABSTRACT FROM AUTHOR]

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In Bangladesh, participation discourse has officially become part of the objectives of the government and international agencies for water management projects since the mid-1990s. At the same historical timeframe, originating from indigenous knowledges Tidal River Management (TRM) has been formalized as a less structural and more natural management intervention to prevent the severe water-logging in the South-west region in the Bangladesh delta. It theoretically constituted a form of participation in the delta management system involving local community groups with government and management authorities. However, multi-stakeholder participation is still very challenging in practices. Even community management approaches are not sustained in delta management practices in Bangladesh. In this research, a socio-technical transformation is defined through a participatory research in the south-west coastal area having both qualitative and quantitative evaluation of changes in the delta management system brought about by TRM practices. This article also analyses the current problems besetting organized community participation in existing management practices and suggests the ways of developing effective multi-stakeholder processes (MSPs) with respect to sustainable management goal in deltas. [ABSTRACT FROM AUTHOR]

The effect of environmental policy on water resources is often challenging to evaluate due to dynamic interactions between people and water, particularly in data‐scarce watersheds. Increasing interactions between society and hydrology present a need to understand causal relations for improved assessment and prediction in complex human‐water systems. Conventional approaches to causal assessment in hydrology are sometimes insufficient due to data scarcity or system complexity. We argue that natural experiments present a promising and complementary avenue for assessing causal relations in such systems. In this spirit, we describe a natural experiment to assess causal effects of the Ganges water treaty, between India and Bangladesh, on streamflow and channel salinity in the Ganges delta in Bangladesh. We apply causal inference to assess the effect of the treaty on streamflow and use the results to generate synthetic ensembles of streamflow and salinity under a realistic scenario (with the treaty) and a counterfactual scenario (without the treaty). We then use synthetic streamflow ensembles to model salinity ensembles. The Ganges water treaty increased dry‐season streamflow in Bangladesh by approximately 18% and decreased channel salinity by approximately 10%. The treaty has the greatest effect on salinity in Bangladesh in the driest years, but the overall effect is small compared with natural variability. We show that our approach accounts for natural hydrologic variability to accurately assess the causal effect of the treaty, compared with a naive approach that greatly overestimates the effect. This research demonstrates the value of natural experiments for causal assessment in coupled human‐water systems. Key Points: Natural experiments and counterfactuals are promising tools for causal assessmentWe use a natural experiment and generate counterfactuals to assess the effect of the Ganges water treaty on streamflow and salinityThe Ganges water treaty plays a modest yet important role in reducing salinity in the delta in Bangladesh [ABSTRACT FROM AUTHOR]

Large-scale water management systems were introduced to the Ganges-Brahmaputra and Mekong Deltas in the latter half of the twentieth century to manage extreme water hazards and increase food production. However, these systems significantly altered their respective hydrological regimes, often creating worse socio-ecological conditions and greater vulnerability to floods and seawater intrusion than existed previously. Despite this history of disaster experience, climate change adaptation measures in the Ganges-Brahmaputra and Mekong Deltas use contemporary socio-ecological conditions as the baseline for disaster mitigation efforts. Paradoxically relying on old approaches to address future climate threats, disaster planners overlook how current conditions in both deltas are unstable outcomes of historical processes. These cases illustrate that large-scale and capital-intensive climate responses may fail to measurably reduce disaster risk. The concept of shifting baselines, borrowed from fisheries science, becomes helpful for selecting more appropriate reference points for disaster mitigation than current conditions. [ABSTRACT FROM AUTHOR]

While there is little dissent in the scientific community that climate change directly correlates to human-caused greenhouse-gas emissions, action to reduce those emissions has not followed from the United States and many other governments around the world. Meanwhile, climate changes are already underway, and will continue to some degree even if emissions are drastically curtailed, thanks to emissions already in the atmosphere. Some countries and states are making their own plans to adapt to expected impacts including higher sea levels, more intense rainfall, droughts, heat waves, and loss of water supplies—and to reduce their local emissions. In this Global Forum, three experts highlight efforts by national and local governments in planning for 2100 and beyond. From the Netherlands, Arthur Mynett (2011); from Bangladesh, Saleemul Huq; and from California, Martha Krebs (2011). Over the months of January and February, this forum will continue at www.thebulletin.org. [ABSTRACT FROM AUTHOR]

Pervasive salinity in soil and water is affecting agricultural yield and the health of millions of delta dwellers in Asia. This is also being exacerbated by climate change through increases in sea level and tropical storm surges. One consequence of this has been a widespread introduction of salt water shrimp farming. Here, we show, using field data and modeling, how changes in climate and land use are likely to result in increased salinization of shallow groundwater in SE Asian mega-deltas. We also explore possible adaptation options. We find that possible future increase of episodic inundation events, combined with salt water shrimp farming, will cause rapid salinization of groundwater in the region making it less suitable for drinking water and irrigation. However, modified land use and water management practices can mitigate the impacts on groundwater, as well as the overlying soil, from future salinization. The study therefore provides guidance for adaptation planning to reduce future salinization in Asian deltas. [ABSTRACT FROM AUTHOR]

The Ganges-Brahmaputra-Meghna (GBM) Delta is one of the largest deltas in the world, covering more than 100,000 km2. The GBM River system transports over one billion tons of sediment annually and delivers ∼750 million tons to the Bay of Bengal, ∼25% of which is advected by tides into the fluvially abandoned western delta plain. Fluvial sediment and water discharge are controlled by the southwest Asian monsoon, with wet season discharge rates exceeding those of the dry season by a factor of five. The Sundarbans National Forest (SNF) is located within the GBM Delta and, covering more than 10,000 km2, is the world's largest continuous mangrove stand. The present rate of sediment delivery allows the SNF platform elevation to keep pace with regional sea level rise, but India's National River Linking Project (NRLP) could decrease the suspended sediment loads of Ganges and Brahmaputra Rivers by 39–75% and 9–25% respectively, and thus may change future sedimentation. In this study, we examine whether sediment stored in the tidal channels could serve as an additional source for platform nourishment, if resuspended and delivered to the mangrove platform throughout the year. Over two field seasons, 70 shallow (<50 cm) sediment cores were collected from the channel banks, imaged using x-radiography to observe fine scale changes in depositional characteristics on tidal channel banks, and subsampled for textural and geochemical analyses. In more than half of the cores examined there is no change in the style of the laminations, suggesting that the processes controlling deposition remain constant throughout the year, despite the seasonal change in the external sediment supply. Cores where the depth of laminations decreases from wet to dry season demonstrate that sediment is being eroded from the banks and advected elsewhere, with the mangrove platform a likely sink. Over 70% of cores showed surface (0–2 cm) grain sizes coarsening from the wet to the dry season, which could be the product of the winnowing of fine sediments as overall sediment supply decreases and material with lower bulk density is preferentially taken away. The findings from textural analysis were further supported by total organic carbon (TOC) profiles, which also indicate constant reworking of sediment on the channel banks throughout the year. • Sediment supply varies across seasons, but deposition remains constant. • Deep, physical reworking of sediment is consistent throughout the year. • Fine sediment is preferentially eroded during the dry season. • Resuspended sediments are available to nourish the platform during the dry season. • Channel erosion is likely an important contributor to platform sedimentation. [ABSTRACT FROM AUTHOR]

Bangladesh, at the confluence of the sediment-laden Ganges and Brahmaputra Rivers, supports an enormous and rapidly growing population (>140 million in 2011), across low-lying alluvial and delta plains that have accumulated over the past few thousand years. It has been identified as one of the most vulnerable places in the world to the impacts of climate change and sea-level rise. Although abundant sediment supply has resulted in accretion on some parts of the coast of Bangladesh, others are experiencing rapid erosion. We report a systematic assessment of rates of shoreline change over a 20-year period from 1989 to 2009, using Landsat satellite images with pixel resolution of 30 m on the ground. A Band ratio approach, using Band-5 divided by Band-2, discriminated the water line on images that were largely cloud-free, adequately registered, and at comparable tidal stages. Rates of shoreline change were calculated for >16,000 transects generated at 50 m intervals along the entire mainland coastline (>1,100 km) and major islands, using the End Point Rate (EPR) method in the Digital Shoreline Analysis System (DSAS) extension in ArcGIS®. Erosion characterises most of the seaward margin of the Sundarbans in western Bangladesh. Retreat rates of up to 20 m/yr are typical, with little evidence that local devastation of the mangrove fringe by Cyclone Sidr in November 2007 had resulted in uncharacteristic long-term rates of retreat where it made landfall. Erosion exceeded accretion in the Barguna Patuakhali coastal zone, most of which eroded at up to 20 m/yr, but with truncation of the southern tip of the Patharghata Upazila at up to 100 m/yr. In Bhola, erosion at rates of up to 120 m/yr were observed along much of the coast, but in the Noakhali Feni coastal zone, similar rates of erosion were balanced by rapid accretion of the main promontory by more than 600 m/yr. Rates of change were more subdued in the Chittagong and Cox's Bazar coastal zones of southeast Bangladesh. Islands in the Meghna estuary were especially dynamic; Hatiya Island accreted along some of its shoreline by 50 km between 1989 and 2009, but lost 65 km through erosion elsewhere, resulting in the island moving south. Similar trends were observed on adjacent islands. The overall area changed relatively little across the entire coastline over the 20-year period with accretion of up to 315 km, countered by erosion of about 307 km. [ABSTRACT FROM AUTHOR]

In the fertile Ganges-Brahmaputra-Meghna (GBM) delta, which spans the boundary from West Bengal in India and Bangladesh, the availability of freshwater is crucial to subsistence livelihoods and protected ecosystems. Controlled by large tides and widely variable river discharge, the delta experiences rising river salinity and salt intrusion, as well as seasonal flooding during the monsoon. Future climate change is projected to increase rainfall in South Asia and river discharge in the GBM system. We address how this process might combine with sea-level rise (SLR) to control future river salinity. Model experiments designed using a range of SLR and climate change scenarios are performed to investigate the forces controlling river salinity in the delta. A flexible mesh modelling approach allows us to investigate the impacts at a wide range of time and space scales. In future projections the disparity between wet and dry season salt intrusion intensifies. In the future, SLR acts to increase river salinity in the GBM delta. During the dry season, this effect is worsened by reduced river discharge. In the wet season, this can be mitigated in the eastern part of the delta by larger seasonal river flows. The central and western delta is dominated by SLR, leading to increased salt intrusion all year round, impacting on water resources and agricultural productivity. In the context of an intensifying hydrological cycle, these conclusions have implications for similar tide-dominated deltas, where SLR can increase tidal range, and therefore exacerbate salt intrusion. • Modelling investigation of processes controlling salt intrusion in GBM delta. • Analysis of future hydrodynamics under sea level rise (SLR) and changing climate. • Projections of hydrodynamics and river salinity under SLR and future climate. • Implications for shortened growing seasons and reduced rice productivity. [ABSTRACT FROM AUTHOR]

A recent erosional problem around a river delta on the Cox's Bazar coast was analyzed in this study. The coastline extends from south to north. Rapid erosion has affected some portions of a 24-km road along the coast, and local authorities have attempted to protect the road via revetment. However, the structure was soon buried with sediment because of a growing sand spit along the river delta, and a new area was eroded. Shoreline positions for a 44-year (1972–2016) period were digitized using Landsat images. From the time stack images, we observed a sand spit growing in a northward direction from 2000 to 2015, and the adjacent erosion area extended in the same direction. We employed a numerical model (MIKE21FM SM) for the computation of wave-driven currents and sediment transport along the coast, and attempted to reproduce recent erosional processes. The numerical result shows that net littoral drift is dominant in the northward direction along the coast, which is the same direction of the spit growth observed in the satellite images. A higher amplitude spit induces higher sediment transport compared to a low amplitude spit because of the difference in local incident wave angles resulting in greater positive gradient of the longshore sediment flux distribution, causing erosion in the downcoast. [ABSTRACT FROM AUTHOR]

Salinity, both in soil and water, is a ubiquitous problem in coastal Bangladesh, particularly in the southwest. Salinity varies at the local scale (5-10 m), but the relative roles of land use and surface geology on salinity variation in near-surface (< 5 m) groundwater are not fully understood. Surface geology, land use and salinity in near-surface (ca. 3 m) groundwater at two small sites (each 0.05 km2) were explored in the southwest coastal region of Bangladesh. The sediments in the near-surface at both sites are fine and hydrometer analyses of cored samples indicate the dominance of silty clay (70%) along with very fine sand (5%), sandy clay (15%) and clay (10%) materials. Salinity variation in near-surface groundwater tends to follow land use rather than surface geology at the scale of our investigations. The study provides evidence of the influence of land use on the near-surface salinity variation and indicates the importance of land-use planning in salinity management in coastal areas. [ABSTRACT FROM AUTHOR]