Partnership for Ocean Level Monitoring: Reinforcing technical capacity of water level data collection, processing and analysis for climate hazard management in the Bangladeshi delta.

Geographically, two-thirds of Bangladesh lies in a vast deltaic plain, formed at the mouth of the Ganges, Brahmaputra and Meghna rivers (GBMD). This delta is the largest and most populated in the world, covering approximately 150,000 km² and home to more than 150 million inhabitants. Floods are frequent, and each year, during the summer monsoon, between 20% and 60% of the country is submerged. In the face of current and future climate disruption, IPCC projections predict in the GBMD: an intensification of floods and extreme events, as well as a worrying rise in mean sea level relative to land elevation. Today, more than 10% of the GBMD is less than one meter above mean sea level and land therein is subsiding, as in the largest deltas of the tropical areas. The future of the GBMD and its ability to remain above water depend on a delicate balance between sea level rise and land subsidence. Quantifying these parameters is essential to guide local policies and adapt strategies to climate change. However, the data available to analyze these phenomena are still very limited in Bangladesh and virtually no data is transmitted to decision-making institutions in real time. This new project, called “Partnership for Ocean Level Monitoring” (POLM), has the main objective of strengthening the technical capacities for observing variations in sea level rise and land level. It is based on the use of "Global Navigation Satellite System" (GNSS) stations, i.e. all satellite positioning systems, to determine in a coupled manner the water level (by Interferometry Reflectometry, IR, method) and the land level. Our project aims to technically support the national institutes dedicated to the study of these parameters and involved in the management of climatic hazards, through: 1. deploying innovative and affordable instrumentation tools; 2. establishing a real-time data transfer network; and 3. contributing to the training of the actors of these institutes, in particular the new generation of female scientists. POLM will enable several proofs of concept adapted to the economic and technical realities of Bangladesh, in particular: a low-cost assembly of stations, which reduces costs by ~50%; and the use of 4G networks, well adapted to the country's satellite coverage, to ensure real-time data transmission. Preliminary results from the analysis of the collected water level measurements, their processing and quality assessment, will be presented, as well as their experimental utilization in numerical models for the representation of the sea level dynamics. This project is part of an international scientific effort to collect coastal oceanographic data, necessary for monitoring global sea level and for predicting ocean rise by regional models. Moreover, the study area where implemented- the GBMD and the coastal belt of Bangladesh- represents one of the pilot site (ID PS-014-01) of the Northern Indian Ocean submitted to the “Coast Predict GlobalCoast” program.