The alarming impact of climate change will be felt on South Asia's major river basins, including the Ganges, Indus and the Brahmaputra, according to a new report.

It also noted that critical intersection of anthropogenic activities and shifting climate patterns can spell dire consequences for about a billion people in the area.

According to the report -- "Elevating River Basin Governance and Cooperation in the HKH Region" -- on these three rivers, there is an immediate need for a climate-resilient approach to river basin management.

The Hindu Kush Himalayas (HKH) are the freshwater sources of South Asia and parts of Southeast Asia. Water originating from their snow, glaciers and rainfall feed the 10 largest river systems in Asia.

The Ganges basin, often regarded as sacred and essential to more than 600 million individuals across the Indian subcontinent, is facing mounting environmental threats. Rapid industrialisation, urbanisation and intensive agricultural practices have exacted a toll on the river's ecological health. The indiscriminate discharge of sewage and industrial waste has severely polluted the water, posing significant risks to both human health and the environment, the report said.

Alongside these anthropogenic activities, the impacts of climate change are exacerbating existing challenges, particularly in the form of escalating flooding and droughts, it said.

The monsoon season -- critical for replenishing water resources -- now brings devastating floods while dry seasons worsen water scarcity, especially in downstream areas such as Bangladesh. These climate-related hazards disproportionately affect vulnerable groups, including women, people with disabilities and marginalised communities, the report added.

Similarly, the Indus river -- a lifeline for more than 268 million people across Pakistan, India, Afghanistan and China -- is under unprecedented stress due to climate change. Rising temperatures, erratic monsoons and environmental degradation are pushing the basin towards a crisis point.

The scale of climate change impacts in the Indus basin is overwhelming, undermining food security, livelihoods and water security, the report said. Variations in the timing and intensity of monsoon rains are already having profound impacts on the health and sustainability of the basin.

On top of that, environmental degradation, including increasing agricultural and industrial pollution, is degrading the riverine environment, adversely affecting freshwater fisheries and eroding the ecological health of the river, the report said.

These challenges are compounded by existing socioeconomic vulnerabilities, further exacerbating the plight of marginalised communities, it added.

In the Brahmaputra basin, climate change -- coupled with dams and development work -- is poised to escalate flooding and droughts, particularly in its lower basin.

Glacial melt rates are expected to rise, impacting water availability across the region. While currently there are no major water diversions in the basin, upstream dam construction and climate change projections are likely to reduce dry season flows in downstream areas, affecting millions of lives, the report stated.

The vulnerability of women, poor and indigenous and marginalised communities is set to escalate as changing socioeconomic drivers converge with projected climate impacts, it added.

According to the report, despite the urgent need for collective action, governance within these basins remains fragmented, with limited multilateral agreements facilitating basin-wide collaboration. Existing treaties and agreements have often failed to address the broader impacts of climate change or involve the marginalised stakeholders.

As these agreements approach expiration, there is an opportunity to adopt more inclusive and resilient approaches to basin governance, leveraging diverse perspectives and expertise, it added.

The report advocates that long-term strategies must prioritise adaptive infrastructure, flexible governance structures and inclusive policies to ensure reliable water supply amid climatic uncertainties.

Recognising the trans-boundary nature of climate impacts, the report stressed on the paramount importance of regional cooperation. Initiatives such as the "HKH Call to Action" provide a framework for collaborative action, fostering trust among basin states and informing evidence-based decision-making.

It also called for a bottom-up approach involving local communities, deeming it essential for effective climate adaptation, with programmes such as "Indus Calling" empowering communities with information and tools for better water management and resilience building. The report advocated for collaborative action and inclusive policies to address the urgent challenges posed by climate change on major river basins in South Asia.

Only through collective efforts can these regions navigate the complexities of climate change and safeguard the livelihoods of millions across the region, the report said.