This research paper presents a systematic literature review on the use of remotely sensed and/or global datasets in distributed hydrological modelling. The study aims to investigate the most commonly used datasets in hydrological models and their performance across different geographical scales of catchments, including the micro-scale (<10 km2), meso-scale (10 km2–1000 km2), and macro-scale (>1000 km2). The analysis included a search for the relation between the use of these datasets to different regions and the geographical scale at which they are most widely used. Additionally, co-authorship analysis was performed on the articles to identify the collaboration patterns among researchers. The study further categorized the analysis based on the type of datasets, including rainfall, digital elevation model, land use, soil distribution, leaf area index, snow-covered area, evapotranspiration, soil moisture and temperature. The research concluded by identifying knowledge gaps in the use of each data type at different scales and highlighted the varying performance of datasets across different locations. The findings underscore the importance of selecting the right datasets, which has a significant impact on the accuracy of hydrological models. This study provides valuable insights into the use of remote sensed and/or global datasets in hydrological modelling, and the identified knowledge gaps can inform future research directions.@en

Hydrological hazards (“hydro-hazards”) are defined as extreme events associated with the occurrence, movement and distribution of water, specifically resulting in floods and droughts. As a result of global climate change these hazards are expected to change in the future, with areas of the globe becoming “hotspots” for the intensification of these extremes. This paper is the first global review of the state- of-the-art research on hotspots for floods and drought. The work follows a systematic literature review of published research, and analyses and categorizes the results of 122 published papers after a methodical screening process. The analysis highlighted the geographical areas where increasing hazards are anticipated (e.g., Europe for both floods and droughts), and those areas of the globe where no significant research has been published (e.g., Russia). The methods used to undertake the research are analyzed and new trends identified. Potential avenues for future research are highlighted, including the incorporation of uncertainty analyses into hydro-hazard assessments, the consideration of multi-hazards and their interconnections, and finally the consideration of dynamic vulnerability and exposure in conjunction with changing hydro-hazards to understanding future risk.@en

Hydrological hazards (“hydro-hazards”) are defined as extreme events associated with the occurrence, movement and distribution of water, specifically resulting in floods and droughts. As a result of global climate change these hazards are expected to change in the future, with areas of the globe becoming “hotspots” for the intensification of these extremes. This paper is the first global review of the state- of-the-art research on hotspots for floods and drought. The work follows a systematic literature review of published research, and analyses and categorizes the results of 122 published papers after a methodical screening process. The analysis highlighted the geographical areas where increasing hazards are anticipated (e.g., Europe for both floods and droughts), and those areas of the globe where no significant research has been published (e.g., Russia). The methods used to undertake the research are analyzed and new trends identified. Potential avenues for future research are highlighted, including the incorporation of uncertainty analyses into hydro-hazard assessments, the consideration of multi-hazards and their interconnections, and finally the consideration of dynamic vulnerability and exposure in conjunction with changing hydro-hazards to understanding future risk.@en

Recent research developments indicate that citizens’ observatories, a novel approach for data collection, management and governance, can provide valuable contributions to strategic delta planning processes. Most citizen observatories are limited in spatial coverage during data collection, according to the citizens’ availability and static locations. However, there are times in which citizens participate as trained volunteers during data collection field campaigns. In this later scenario, an important aspect in organising and maintaining citizen observatories is having a clear plan for data gathering activities, including determination of routes to be followed by these citizens. This article addresses the issue of determining such routes (called pathways) related to the specific problem of gathering data in deltaic areas, which are composed of intricate canals and wetlands. Data collection activities consist of citizens acquiring images and videos with mobile phones at predetermined locations (Points of Interest) that are only accessible by boats. A pathway selection approach is presented, supported by a hydrodynamic model, developed to capture the specific processes of the delta. The aim of the approach is to define: where to send the citizens to fulfil stakeholders’ interest and planning goals, how to reach these points and which pathways should be selected (prioritised based on such interests), considering possible flood patterns. The developed methodology is part of an ongoing H2020 funded research. The proof of concept is carried out in the Sontea-Fortuna area, of the Danube Delta, which, similar to many wetlands, contains a large variety of unique, endemic species. With the developed approach, pathways to be followed by citizens during data collection campaigns were generated and scored considering local interests. Analysis of the boat’s accessibility into the delta during different hydrological scenarios showed that the wetland is more accessible than expected, hence the proposed pathway approach was useful in prioritizing some canals over others. The determined pathways will be applied in field campaigns. The approach can be applied to other delta regions with different environmental problems, such as water quality or ecosystem assessment, contributing to the organisation of effective active citizen data collection.@en

Recent research developments indicate that citizens’ observatories, a novel approach for data collection, management and governance, can provide valuable contributions to strategic delta planning processes. Most citizen observatories are limited in spatial coverage during data collection, according to the citizens’ availability and static locations. However, there are times in which citizens participate as trained volunteers during data collection field campaigns. In this later scenario, an important aspect in organising and maintaining citizen observatories is having a clear plan for data gathering activities, including determination of routes to be followed by these citizens. This article addresses the issue of determining such routes (called pathways) related to the specific problem of gathering data in deltaic areas, which are composed of intricate canals and wetlands. Data collection activities consist of citizens acquiring images and videos with mobile phones at predetermined locations (Points of Interest) that are only accessible by boats. A pathway selection approach is presented, supported by a hydrodynamic model, developed to capture the specific processes of the delta. The aim of the approach is to define: where to send the citizens to fulfil stakeholders’ interest and planning goals, how to reach these points and which pathways should be selected (prioritised based on such interests), considering possible flood patterns. The developed methodology is part of an ongoing H2020 funded research. The proof of concept is carried out in the Sontea-Fortuna area, of the Danube Delta, which, similar to many wetlands, contains a large variety of unique, endemic species. With the developed approach, pathways to be followed by citizens during data collection campaigns were generated and scored considering local interests. Analysis of the boat’s accessibility into the delta during different hydrological scenarios showed that the wetland is more accessible than expected, hence the proposed pathway approach was useful in prioritizing some canals over others. The determined pathways will be applied in field campaigns. The approach can be applied to other delta regions with different environmental problems, such as water quality or ecosystem assessment, contributing to the organisation of effective active citizen data collection.@en

Recent research developments indicate that citizens’ observatories, a novel approach for data collection, management and governance, can provide valuable contributions to strategic delta planning processes. Most citizen observatories are limited in spatial coverage during data collection, according to the citizens’ availability and static locations. However, there are times in which citizens participate as trained volunteers during data collection field campaigns. In this later scenario, an important aspect in organising and maintaining citizen observatories is having a clear plan for data gathering activities, including determination of routes to be followed by these citizens. This article addresses the issue of determining such routes (called pathways) related to the specific problem of gathering data in deltaic areas, which are composed of intricate canals and wetlands. Data collection activities consist of citizens acquiring images and videos with mobile phones at predetermined locations (Points of Interest) that are only accessible by boats. A pathway selection approach is presented, supported by a hydrodynamic model, developed to capture the specific processes of the delta. The aim of the approach is to define: where to send the citizens to fulfil stakeholders’ interest and planning goals, how to reach these points and which pathways should be selected (prioritised based on such interests), considering possible flood patterns. The developed methodology is part of an ongoing H2020 funded research. The proof of concept is carried out in the Sontea-Fortuna area, of the Danube Delta, which, similar to many wetlands, contains a large variety of unique, endemic species. With the developed approach, pathways to be followed by citizens during data collection campaigns were generated and scored considering local interests. Analysis of the boat’s accessibility into the delta during different hydrological scenarios showed that the wetland is more accessible than expected, hence the proposed pathway approach was useful in prioritizing some canals over others. The determined pathways will be applied in field campaigns. The approach can be applied to other delta regions with different environmental problems, such as water quality or ecosystem assessment, contributing to the organisation of effective active citizen data collection.@en

Recent research developments indicate that citizens’ observatories, a novel approach for data collection, management and governance, can provide valuable contributions to strategic delta planning processes. Most citizen observatories are limited in spatial coverage during data collection, according to the citizens’ availability and static locations. However, there are times in which citizens participate as trained volunteers during data collection field campaigns. In this later scenario, an important aspect in organising and maintaining citizen observatories is having a clear plan for data gathering activities, including determination of routes to be followed by these citizens. This article addresses the issue of determining such routes (called pathways) related to the specific problem of gathering data in deltaic areas, which are composed of intricate canals and wetlands. Data collection activities consist of citizens acquiring images and videos with mobile phones at predetermined locations (Points of Interest) that are only accessible by boats. A pathway selection approach is presented, supported by a hydrodynamic model, developed to capture the specific processes of the delta. The aim of the approach is to define: where to send the citizens to fulfil stakeholders’ interest and planning goals, how to reach these points and which pathways should be selected (prioritised based on such interests), considering possible flood patterns. The developed methodology is part of an ongoing H2020 funded research. The proof of concept is carried out in the Sontea-Fortuna area, of the Danube Delta, which, similar to many wetlands, contains a large variety of unique, endemic species. With the developed approach, pathways to be followed by citizens during data collection campaigns were generated and scored considering local interests. Analysis of the boat’s accessibility into the delta during different hydrological scenarios showed that the wetland is more accessible than expected, hence the proposed pathway approach was useful in prioritizing some canals over others. The determined pathways will be applied in field campaigns. The approach can be applied to other delta regions with different environmental problems, such as water quality or ecosystem assessment, contributing to the organisation of effective active citizen data collection.@en

Recent research developments indicate that citizens’ observatories, a novel approach for data collection, management and governance, can provide valuable contributions to strategic delta planning processes. Most citizen observatories are limited in spatial coverage during data collection, according to the citizens’ availability and static locations. However, there are times in which citizens participate as trained volunteers during data collection field campaigns. In this later scenario, an important aspect in organising and maintaining citizen observatories is having a clear plan for data gathering activities, including determination of routes to be followed by these citizens. This article addresses the issue of determining such routes (called pathways) related to the specific problem of gathering data in deltaic areas, which are composed of intricate canals and wetlands. Data collection activities consist of citizens acquiring images and videos with mobile phones at predetermined locations (Points of Interest) that are only accessible by boats. A pathway selection approach is presented, supported by a hydrodynamic model, developed to capture the specific processes of the delta. The aim of the approach is to define: where to send the citizens to fulfil stakeholders’ interest and planning goals, how to reach these points and which pathways should be selected (prioritised based on such interests), considering possible flood patterns. The developed methodology is part of an ongoing H2020 funded research. The proof of concept is carried out in the Sontea-Fortuna area, of the Danube Delta, which, similar to many wetlands, contains a large variety of unique, endemic species. With the developed approach, pathways to be followed by citizens during data collection campaigns were generated and scored considering local interests. Analysis of the boat’s accessibility into the delta during different hydrological scenarios showed that the wetland is more accessible than expected, hence the proposed pathway approach was useful in prioritizing some canals over others. The determined pathways will be applied in field campaigns. The approach can be applied to other delta regions with different environmental problems, such as water quality or ecosystem assessment, contributing to the organisation of effective active citizen data collection.@en

Compared to coastal areas, river deltas which are located in coastal zone, have complex morphologies, because river waters and sediments are transported through the deltas into the sea. A delta can have many elements included, such as barrier islands, multiple estuaries, sand beaches, or mud coasts. It can be crisscrossed by rivers emanating from different sources and carrying different types of sediments; which differentiate the segments of the coast. Generally, deltas are fertile and highly productive, attracting agricultural activities and trade and thus densely populated. The physical properties of deltas and anthropogenic activities make them vulnerable to the effects of the changing climate; however when evaluation of vulnerabilities is important many coastal deltas lack even the most basic necessary data (e.g water level) for performing such a task. Data availability is one of the most important factors for analysis, assessment and modeling of physical and other phenomena related to river and coastal systems. Although lower Niger delta is classified as one of the deltas of the world vulnerable to the effects of climate change, it has little availability of data for hydrologic and hydraulic modeling. Present paper will show how to model the possible effect of a rise in sea levels on the lower Niger delta, by dividing its coastline into 54 segments based on slope, elevation and presence of large estuaries. The segments are analyzed for vulnerability to flooding, erosion and inundation. The parts identified as the most vulnerable are modeled using Deltares' DFlow modelling methodology, using a flexible mesh for discretization of the modeled area. Satellite derived DEM is used to calculate an upstream rating curve for the Bonny River, and to provide topographic data. Sea level rise is represented by changes in the tidal level to reflect IPCC predictions of sea levels by 2050 and 2100. The results are analyzed for flooding and inundation, increase in land loss, water depth and flood extent as compared with no sea level rise scenarios. Also, dry and wet land losses are mapped and quantified within a GIS environment.@en

Citizen contributions to science have been successfully implemented in many fields, and water resources is one of them. Through citizens, it is possible to collect data and obtain a more integrated decision-making process. Specifically, data scarcity has always been an issue in flood modelling, which has been addressed in the last decades by remote sensing and is already being discussed in the citizen science context. With this in mind, this article aims to review the literature on the topic and analyse the opportunities and challenges that lie ahead. The literature on monitoring, mapping and modelling, was evaluated according to the flood-related variable citizens contributed to. Pros and cons of the collection/analysis methods were summarised. Then, pertinent publications were mapped into the flood modelling cycle, considering how citizen data properties (spatial and temporal coverage, uncertainty and volume) are related to its integration into modelling. It was clear that the number of studies in the area is rising. There are positive experiences reported in collection and analysis methods, for instance with velocity and land cover, and also when modelling is concerned, for example by using social media mining. However, matching the data properties necessary for each part of the modelling cycle with citizen-generated data is still challenging. Nevertheless, the concept that citizen contributions can be used for simulation and forecasting is proved and further work lies in continuing to develop and improve not only methods for collection and analysis, but certainly for integration into models as well. Finally, in view of recent automated sensors and satellite technologies, it is through studies as the ones analysed in this article that the value of citizen contributions, complementing such technologies, is demonstrated.@en

Advances in sensing approaches have allowed hydrological and hydrodynamic models to be implemented in a wide range of cases: from complex flash-floods to global models. However, such approaches are new and the limits of their accuracy and employability in different contexts are still not fully known. Therefore, the objective of this study is to test a citizen science sensing approach ability to improve hydrological and hydrodynamic modelling of an urbanized catchment. Results indicate the conditions under which data can be useful for model.@en

Advances in sensing approaches have allowed hydrological and hydrodynamic models to be implemented in a wide range of cases: from complex flash-floods to global models. However, such approaches are new and the limits of their accuracy and employability in different contexts are still not fully known. Therefore, the objective of this study is to test a citizen science sensing approach ability to improve hydrological and hydrodynamic modelling of an urbanized catchment. Results indicate the conditions under which data can be useful for model.@en

Wastewater effluents from irrigation and the domestic and industrial sectors have serious impacts in deteriorating water quality in many rivers, particularly in areas under tidal influence. There is a need to develop an approach that considers the impact of human and natural causes of salinization. This study uses a multi-objective optimization–simulation model to investigate and describe the interactions of such impacts in the Shatt al-Arab River, Iraq. The developed model is able to reproduce the salinity distribution in the river given varying conditions. The salinity regime in the river varies according to different hydrological conditions and anthropogenic activities. Due to tidal effects, salinity caused by drainage water is seen to intrude further upstream into the river. The applied approach provides a way to obtain optimal solutions where both river salinity and deficit in water supply can be minimized. The approach is used for exploring the trade-off between these two objectives.@en

Lake Taihu is a shallow, wind-driven lake where eutrophication is always a serious problem. The study presented herein investigates the effect of wind on the eutophication of the lake, by using a two-dimensional (2D) hydrodynamic model coupled with a 2D water quality model. The 2D water quality model looks in particular at the water quality situation of Lake Taihu in the year 2008 and predicts future changes in the algae bloom situation. The Delft3D modelling tool was used to build the hydrodynamic model based on the measured geomorphologic and meteorological data of Lake Taihu. Three different sets of wind conditions (no wind, constant wind and measured wind) were considered as wind effects on the water level and velocity, in both the wet and dry seasons. Based on the calibrated hydrodynamic model a 2D water quality model was built which was calibrated based on estimated data for nutrient loads. A one-year hydrodynamic simulation was performed, in order to determine the water quality situation of Lake Taihu. The estimated nutrient loads included total nitrogen (TN) and total phosphorus (TP) concentrations. The estimates are based on the population of cities around Lake Taihu, and the wastewater treatment plant capacity of the provinces of Jiangsu and Zhejiang, where the main sources of pollutants come from. Two time periods (spring and autumn) of algae blooms development for the year 2008 are presented. The results of the study indicate that: 1) the hydrodynamic model with constant wind conditions (southeast, 5m/s) showed better results than the one where measured wind conditions were used, simply because the measured wind data is insufficient at the moment; 2) the model clearly represents the water quality to an acceptable degree; 3) an increase in population in the area would lead to an increase in the maximum value of algae concentration from 35% to 76%; 4) if there is an improvement in technology at the wastewater treatment plant, then the maximum value of algae concentration will be between 17% and 42%.@en

Response strategies determine the resilience of an area to effects of sea level rise. Strategies that are sustainable are those that do not negatively affect the environment, biodiversity and community life of the people. The paper discusses response strategies practiced in the Niger delta to combat effects of sea level rise like: flooding, erosion, inundation, storm surge, and intrusion of sea salt. Local responses to these natural hazards and the degree of effectiveness of the methods in enabling the people return to their normal lives are reviewed for their suitability as future adaptation strategies. GIS and remote sensing analysis of slope and topography show the Niger delta is vulnerable to further flooding, inundation, and erosion as a result of sea level rise. Based on a ‘business as usual’ scenario, the GIS based bathtub approach is used to calculate and map possible inundation extents for the Niger delta under sea level rise conditions. As the Niger delta is subsiding due to oil and gas exploitation, relative sea level rise (RSLR) values for the Niger delta are obtained by adding measured subsidence values (7 mm and 25 mm) to predicted eustatic sea level rise values (19 mm by 2030 and 35 mm by 2050); resulting in RSLR of 0.14–0.96 m by 2030 and 2050. With subsidence at 7 mm/year and a RSLR of 0.14 m, results for 2030 shows an inundation extent of 1119.3 km2 which is 4.6% of the total surface area; subsidence of 25 mm/year (SLR = 0.44 m) gives an inundation extent of 1254.0 km2 which is 5.2% of the surface area. Results for 2050 show that a rise of 0.29 m (subsidence = 7 mm/year) will cause an inundation extent of 1175.9 km2 which is 4.9% of the total surface area, and RSLR of 0.96 m (subsidence = 25 mm/year) inundates 1633.0 km2 which is 6.8% of the surface area. Although the literature shows local practices have helped people to cope with the challenges posed by flooding, erosion, inundation, and inland intrusion of sea salts, however some of the practices have disadvantages that make them undesirable for inclusion in future planning. Sustainable local practices in the Niger delta include: planting of Bamboo trees for erosion control, use of sandbags as bridges and dikes (flood control), use of flood receptor pits as temporary flood water reservoirs, and community legislation against sand mining and indiscriminate tree felling. Further studies on the limitations of the local resilience practices in the Niger delta is recommended.@en

Response strategies determine the resilience of an area to effects of sea level rise. Strategies that are sustainable are those that do not negatively affect the environment, biodiversity and community life of the people. The paper discusses response strategies practiced in the Niger delta to combat effects of sea level rise like: flooding, erosion, inundation, storm surge, and intrusion of sea salt. Local responses to these natural hazards and the degree of effectiveness of the methods in enabling the people return to their normal lives are reviewed for their suitability as future adaptation strategies. GIS and remote sensing analysis of slope and topography show the Niger delta is vulnerable to further flooding, inundation, and erosion as a result of sea level rise. Based on a ‘business as usual’ scenario, the GIS based bathtub approach is used to calculate and map possible inundation extents for the Niger delta under sea level rise conditions. As the Niger delta is subsiding due to oil and gas exploitation, relative sea level rise (RSLR) values for the Niger delta are obtained by adding measured subsidence values (7 mm and 25 mm) to predicted eustatic sea level rise values (19 mm by 2030 and 35 mm by 2050); resulting in RSLR of 0.14–0.96 m by 2030 and 2050. With subsidence at 7 mm/year and a RSLR of 0.14 m, results for 2030 shows an inundation extent of 1119.3 km2 which is 4.6% of the total surface area; subsidence of 25 mm/year (SLR = 0.44 m) gives an inundation extent of 1254.0 km2 which is 5.2% of the surface area. Results for 2050 show that a rise of 0.29 m (subsidence = 7 mm/year) will cause an inundation extent of 1175.9 km2 which is 4.9% of the total surface area, and RSLR of 0.96 m (subsidence = 25 mm/year) inundates 1633.0 km2 which is 6.8% of the surface area. Although the literature shows local practices have helped people to cope with the challenges posed by flooding, erosion, inundation, and inland intrusion of sea salts, however some of the practices have disadvantages that make them undesirable for inclusion in future planning. Sustainable local practices in the Niger delta include: planting of Bamboo trees for erosion control, use of sandbags as bridges and dikes (flood control), use of flood receptor pits as temporary flood water reservoirs, and community legislation against sand mining and indiscriminate tree felling. Further studies on the limitations of the local resilience practices in the Niger delta is recommended.@en

Response strategies determine the resilience of an area to effects of sea level rise. Strategies that are sustainable are those that do not negatively affect the environment, biodiversity and community life of the people. The paper discusses response strategies practiced in the Niger delta to combat effects of sea level rise like: flooding, erosion, inundation, storm surge, and intrusion of sea salt. Local responses to these natural hazards and the degree of effectiveness of the methods in enabling the people return to their normal lives are reviewed for their suitability as future adaptation strategies. GIS and remote sensing analysis of slope and topography show the Niger delta is vulnerable to further flooding, inundation, and erosion as a result of sea level rise. Based on a ‘business as usual’ scenario, the GIS based bathtub approach is used to calculate and map possible inundation extents for the Niger delta under sea level rise conditions. As the Niger delta is subsiding due to oil and gas exploitation, relative sea level rise (RSLR) values for the Niger delta are obtained by adding measured subsidence values (7 mm and 25 mm) to predicted eustatic sea level rise values (19 mm by 2030 and 35 mm by 2050); resulting in RSLR of 0.14–0.96 m by 2030 and 2050. With subsidence at 7 mm/year and a RSLR of 0.14 m, results for 2030 shows an inundation extent of 1119.3 km2 which is 4.6% of the total surface area; subsidence of 25 mm/year (SLR = 0.44 m) gives an inundation extent of 1254.0 km2 which is 5.2% of the surface area. Results for 2050 show that a rise of 0.29 m (subsidence = 7 mm/year) will cause an inundation extent of 1175.9 km2 which is 4.9% of the total surface area, and RSLR of 0.96 m (subsidence = 25 mm/year) inundates 1633.0 km2 which is 6.8% of the surface area. Although the literature shows local practices have helped people to cope with the challenges posed by flooding, erosion, inundation, and inland intrusion of sea salts, however some of the practices have disadvantages that make them undesirable for inclusion in future planning. Sustainable local practices in the Niger delta include: planting of Bamboo trees for erosion control, use of sandbags as bridges and dikes (flood control), use of flood receptor pits as temporary flood water reservoirs, and community legislation against sand mining and indiscriminate tree felling. Further studies on the limitations of the local resilience practices in the Niger delta is recommended.@en

Bangladesh, occupying low-lying floodplains and tidal plains, has one of the largest and the most disaster-prone populous deltas in the world. The Bengal Delta is a tide-dominated delta, where tides play the key role in the sediment dispersal process and in shaping the delta. There are many studies and reports on river-dominated deltas, but research is sparse on tide-dominated deltas. The Ganges and Brahmaputra Rivers, which combined form one of the three largest riverine sources of water and sediment for the world's oceans, have developed the Bengal Delta to its present form with an aerial extent of 104 km2. About 1012 m3 of water with 109 tonnes of sediment per year make this system morphologically active. In the last five decades, the Bengal Delta has prograded at a rate of 17 km2/y, whereas most large deltas elsewhere in the world suffered from sediment starvation. Delta progradation always makes the river system unstable, and rapid changes cause the delta to become dynamic. Sea level rise induced by unequivocal climate change and subsidence would make the delta more vulnerable in the coming decades. Although some literature is available on the millennium-scale development process of the Bengal Delta, sound knowledge on the decade-to century-scale processes of the delta development for facing the threats of climate change and deltaic subsidence is limited. In addition, there are significant differences in opinions and widely varying findings in the literature to the response of the delta to different natural and human interventions. Against this backdrop, relevant available literature on Bengal Delta and deltas elsewhere in the world, is reviewed and evaluated to provide direction for future research that would help to form a way out of the present situation and a way into sustainable planning for this delta.@en

Bangladesh, occupying low-lying floodplains and tidal plains, has one of the largest and the most disaster-prone populous deltas in the world. The Bengal Delta is a tide-dominated delta, where tides play the key role in the sediment dispersal process and in shaping the delta. There are many studies and reports on river-dominated deltas, but research is sparse on tide-dominated deltas. The Ganges and Brahmaputra Rivers, which combined form one of the three largest riverine sources of water and sediment for the world's oceans, have developed the Bengal Delta to its present form with an aerial extent of 104 km2. About 1012 m3 of water with 109 tonnes of sediment per year make this system morphologically active. In the last five decades, the Bengal Delta has prograded at a rate of 17 km2/y, whereas most large deltas elsewhere in the world suffered from sediment starvation. Delta progradation always makes the river system unstable, and rapid changes cause the delta to become dynamic. Sea level rise induced by unequivocal climate change and subsidence would make the delta more vulnerable in the coming decades. Although some literature is available on the millennium-scale development process of the Bengal Delta, sound knowledge on the decade-to century-scale processes of the delta development for facing the threats of climate change and deltaic subsidence is limited. In addition, there are significant differences in opinions and widely varying findings in the literature to the response of the delta to different natural and human interventions. Against this backdrop, relevant available literature on Bengal Delta and deltas elsewhere in the world, is reviewed and evaluated to provide direction for future research that would help to form a way out of the present situation and a way into sustainable planning for this delta.@en