The Ganges delta in Bangladesh. Emre Akkoyun/ShutterstockBangladesh is known as the land of rivers and flooding, despite almost all of its water originating outside the territory. The fact that 80% of rivers that flow through Bangladesh have their sources in a neighbouring country, can make access to freshwater in Bangladesh fraught. And the country’s fast-growing cities and farms – and the warming global climate – are turning up the pressure.In a recent analysis, my colleagues and I found that four out of the ten rivers that flow through Bangladesh have failed to meet a set of conditions known as their “safe operating space”, meaning that the flow of water in these rivers is below the minimum necessary to sustain the social-ecological systems that rely on them. These rivers included the Ganges and Old Brahmaputra, as well as Gorai and Halda.This puts a safe and reliable food and water supply not to mention the livelihoods of millions of fishers, farmers and other people in the region, at risk.Water flow on the remaining six rivers may be close to a dangerous state too, due to the construction of hydropower dams and reservoirs, as well as booming irrigated agriculture.Get your news from actual experts, straight to your inbox. Sign up to our daily newsletter to receive all The Conversation UK’s latest coverage of news and research, from politics and business to the arts and sciences.The concept of a safe operating space was devised by Stockholm University researchers in 2009 and typically assesses the Earth’s health as a whole by defining boundaries such as climate warming, water use and biodiversity loss which become dangerous to humanity once exceeded. A 2023 update to this research found that six of the nine defined planetary boundaries have been transgressed. Since the Bangladesh delta is one of the world’s largest and most densely populated (home to around 170 million people), we thought it prudent to apply this thinking to the rivers here. We found that food, fisheries and the world’s largest intertidal mangrove forest, a haven for rich biodiversity, are all under strain from water demand in growing cities such as Dhaka.The knock-on effectsDuring all seasons but winter, river flows in the Bangladesh delta have fallen over the past three decades. No river in the Bangladesh delta is within its safe operating space. Kabir et al. (2024) Our analysis highlights the limits of existing political solutions. The ability of the Ganges river to support life and society is severely strained, despite the Ganges water sharing treaty between India and Bangladesh, which was signed in 1996.Rivers in Bangladesh have shaped the economy, environment and culture of South Asia since the dawn of human civilisation here. And humans are not the only species suffering. Hilsha (Tenualosa ilisha), related to the herring, is a fish popular for its flavour and delicate texture. It contributes 12% to national fish production in Bangladesh but has become extinct in the upper reaches of the Ganges due to the reduction of water flow. Excessive water extraction upstream, primarily through the Farakka barrage, a dam just over the border in the Indian state of West Bengal, has also raised the salinity of the Gorai river. A healthy river flow maintains a liveable balance of salt and freshwater. As river flows have been restricted, salinity has crept up, particularly in coastal regions that are also beset by sea level rise. This damages freshwater fisheries, farm yields and threatens a population of freshwater dolphins in the Ganges.Low river flows and increasing salinisation now threaten the destruction of the world’s largest mangrove forest, the loss of which would disrupt the regional climate of Bangladesh, India and Nepal. It would also release a lot of stored carbon to the atmosphere, accelerating climate change and the melting of snow and ice in the Himalayan mountain chain.Resilience to climate changeSolving this problem is no simple task. It will require cooperation across national boundaries and international support to ensure fair treaties capable of managing the rivers sustainably, restoring their associated ecosystems and maintaining river flows within their safe operating spaces. The mighty Ganges is running dry in some parts of Bangladesh during the hotter months. Md Sarwar Hossain This is particularly challenging in the Bangladesh delta, which contains rivers that drain many countries, including China, India, Nepal and Pakistan. The political regimes in each country might oppose transboundary negotiations, which could nevertheless resolve conflict over water which is needed to sustain nearly 700 million people.There have been success stories, however. The Mekong river commission between Cambodia, Laos, Thailand and Vietnam is a useful template for bilateral and multilateral treaties with India and Nepal for the Ganges, and China and Bhutan for the Jamuna river.Tax-based water sharing can help resolve conflicts and decide water allocation between countries in the river basin. The countries using more water would pay more tax and the revenue would be redistributed among the other countries who share rivers in the treaty. Additionally, water sharing should be based on the historical river flow disregarding existing infrastructure and projections of future changes.Reducing deforestation, alternating land use and restoring wetlands could enhance resilience to flooding and drought and ensure water security in the Bangladesh delta. Ultimately, to secure a safe operating space for the rivers here is to secure a safe future for society too.Don’t have time to read about climate change as much as you’d like?Get a weekly roundup in your inbox instead. Every Wednesday, The Conversation’s environment editor writes Imagine, a short email that goes a little deeper into just one climate issue. Join the 45,000+ readers who’ve subscribed so far.Md Sarwar Hossain does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.