Impact of Salinity on Agriculture of Ganges-Brahmaputra-Meghna Delta and Mekong delta

Coastal regions and deltas are heavily populated hubs of economic activities and underpinning global and regional food security. Deltas globally are facing increasing risks of salinization as sea water levels rise and seawater intrudes further upstream. Salinization is further amplified during dry season by groundwater extraction, reduction in water inflows and local agricultural practices. However, the exact dynamics of salinization in rivers, coasts and deltas, and the associated rise in salinity now and in the future, remain poorly understood. To develop a better understanding of how salinization processes work in coastal regions and its potential impact on current and future food production, a salinity assessment approach was developed and tested in the deltas of the Ganges Brahmaputra Meghna rivers in southwest Bangladesh (henceforth termed as Bengal delta) and the Mekong. Both deltas are among the world’s most vulnerable regions to climate change and increasing salinity and are major rice producers. With special focus on these 2 deltas, the aim of this study is to: 1. Identify salinity hotspot areas in the Bengal and Mekong deltas for the existing situation of the year 2010, by combining the effects of water and soil salinity; 2. Project salinity hotspot areas in the future (2050) for the scenario SSP1) RCP 4.5 (Representative Concentration Pathway), by using projection of water salinity from literatures and developing a machine learning model to predict future soil salinity; 3. Assess the vulnerability of food production to salinity - using rice as an example - by identifying the cropping areas under different salinity thresholds for yearly maximum salinity. A salinity map indicating the areas prone to salinization (salinity hotspots) is created, using data of surface water and topsoil salinity levels, thus composing ‘water and soil salinity’ data. The resulting hotspots are the areas upstream of Sundarbans which lack fresh water flow from upstream and in the Mekong delta the highest salinity hotspots are located in the low-lying southwest region and along the southern coastal areas. In both the Bengal and Mekong delta, soil salinity is projected to increase compared to the current situation with spatial variability. The Bengal delta areas further inland will have higher salinity and the Mekong delta is expected to increase in the eastern part. The combined analysis of soil and water salinity hotspots also depicts that the total area considered as high to medium saline will increase for both deltas and move further inland compared to present salinity conditions. Finally, the rice area growing under saline areas for the current and future situation was analysed. In both deltas, it is clear the rice areas affected by medium to high salinity will increase substantially in the future. As reduction of yield depends on many more factors, besides the level of salinity, and because the damage will differ with various levels of salinity at different stages of the crop, yield impact could not yet be established. Further studies may increase the understanding. It will also be relevant to collect observed data at field level, to further substantiate the results. From this analysis, it is clear that to sustain the current level of productivity, an active transition towards adaptive saline agriculture will be required involving concerted action by farmers, government agencies, agricultural research organizations, civil society, the private sector and development partners.