Climate Change and Flood Risks in the Ganga and Brahmaputra Basins

According to a new report, the alarming impact of climate change has started affecting South Asia’s major river basins, including the Ganges, Indus, and the Brahmaputra. The Brahmaputra and Ganges basins, two of the most significant river systems in South Asia, play a crucial role in the lives of millions, shaping the economies, cultures, and environments of the regions they traverse.

Understanding the Basins

Variations in the timing and intensity of monsoon rains profoundly impact the health and sustainability of the basins. However, these basins are also prone to a myriad of challenges, from devastating floods to soil erosion, impacting both human settlements and natural ecosystems. With climate change exacerbating these risks, the need for effective management strategies has never been more cardinal. Under the effect of climate change and climate warming, extreme weather events such as monsoon-induced floods have amplified, leading to an increased frequency of natural hazards like floods, cyclones, landslides, and heavy rains. Globally, floods are among the most devastating natural hazards that cause substantial damage to infrastructure, humans, and agriculture. Monsoon season flooding in the Brahmaputra and Ganges has become more intense in some areas, resulting in longer rain spells, saturating soils, and increased runoffs. Indian rivers, especially those in flood-prone regions in India, are highly prone to annual floods due to upstream rainfall. Nearly 75%[1] of the total Indian rainfall is concentrated in the four monsoon months (June-September), leading to widespread flooding in a few states. Floods in India majorly affect Uttar Pradesh, Bihar, West Bengal, and Assam. The worst affected sub-basins are those of the Ganga and Brahmaputra.

Figure 1: Indian River Basins with Catchment Areas

Over the past few years, India has witnessed a three-fold rise in rainfall and waterlogging incidents across eastern, central, and northern India. The monsoon rains from the southwest cause flooding in rivers such as Yamuna, Ganga, Brahmaputra, etc. The intense monsoon swells the banks, which leads to flooding in adjacent areas. Here’s a concise overview of Flood-Prone Rivers and States in India facing recurring problems of flooding:

The overflowing Brahmaputra River brings floods in Assam and neighboring states annually.
The Ganga River flooding affects the states of Uttarakhand, Bihar, Uttar Pradesh, and West Bengal.
The Kosi River (Sorrow of Bihar) annually floods around 21,000 km² of fertile agricultural lands, adversely impacting Bihar’s rural economy.
The Yamuna River causes severe flooding in Delhi and surrounding areas.
Mahanadi River flooding impacts Orissa.

Figure 2 indicates that the most flood-prone areas in India are falling under the Ganges and Brahmaputra basins in the Indo-Gangetic-Brahmaputra plains in North and Northeast India, which carry 60% of the total river flow. In this article, we have focused particularly on the Ganges and Brahmaputra Basins.

Brahmaputra Fury in Monsoons

In India, the Brahmaputra basin spreads over Arunachal Pradesh, Assam, West Bengal, Meghalaya, Nagaland, and Sikkim and extends over an area[2] of 194,413 sq.km. Most of the basin lying in Assam and Meghalaya consists of hills, forests, and the Brahmaputra valley, which is about 80 km wide on average. The basin experiences heavy rainfall, and rainfall distribution in the Brahmaputra basin differs in different parts. In the southern slopes of the Himalayan region, falling in this basin experiences rainfall of over 6000 mm. Unlike the peninsular rivers of India, these Himalayan rivers are perennial as glaciers and snowmelt feed them throughout the year. With increased warming due to climate change, melting snow caps and glaciers have also intensified, increasing the risk of frequent flooding.

The Brahmaputra River has a long history of devastating floods in the state of Assam, as depicted in Figure 3. Assam’s geography, strategic location, and moisture-laden monsoon winds result in extreme precipitation, often exceeding 300-400 mm per month, a major cause of extreme annualized flooding events. Increased frequency of glaciers and snow caps melting extreme rainfall events due to global warming and climate change will likely escalate flooding, particularly in its lower basin. Over 50 tributaries feed the river, increasing the water level and causing devastating floods every year.

Figure 3: Events Timeline via infographic

If we look at flooding incidents in 2024 in the northeast, despite the monsoon trough being situated in the foothills of the Himalayas in Arunachal Pradesh, the major devastations occurred in Assam. Assam had already recorded a 15%^[3] positive deviation in rainfall for the month of July, which led to devastating floods across the entire state. The state of Assam had already received 160.5 mm of rainfall against the normal of 139.3mm in just 9 days (between July 1 and July 9, 2024). Figure 4 indicates the increased rainfall from June 1 to July 9 in the northeastern states of India. Due to the heavy rainfall, river water levels in the Brahmaputra basin and its tributaries have risen, resulting in flooding in additional areas. Excess rainfall in the state, along with the rainwater carried from Arunachal Pradesh through the Brahmaputra River, and the excess rainfall in Manipur also worsened the situation, resulting in floods and devastating landslides in Assam. Floodwater damaged several districts’ embankments, roads, bridges, and other infrastructure. A total of 2,561 houses were reported damaged fully and partially. The floods also severely impacted Kaziranga National Park, a UNESCO World Heritage site.

Figure 4: Increase in rainfall witnessed in the month of June 2024

Flooding in the Ganges Basin

Unlike the Brahmaputra basin, the Ganges basin is much more diverse, passing through many Indian states. It passes through the states of Uttarakhand, Uttar Pradesh, Haryana, Delhi, Rajasthan, Madhya Pradesh, Chhattisgarh, Jharkhand, and West Bengal before draining into the Bay of Bengal (Figure 5).

Figure 5: Course of River Ganges in India (Source: NRSC)

The Ganges Basin has the highest population density among all basins in the Indian subcontinent. During the monsoon season, heavy rainfall in the Himalayas causes water levels to rise significantly in many of the Ganges’s central and eastern tributaries, leading to widespread flooding across several states falling in the Ganges Basin. Additionally, the Ganges is India’s most silt-laden river, and the accumulation of silt raises the riverbed, further increasing the risk of flooding during the monsoon. Other factors contributing to flooding include encroachment on floodplains, riverside sand mining, and inadequate waste management, such as improper sewage and effluent discharge.

Figure 6: Past Trends of Flooding in the River Ganges

Past flooding in the Ganges Basin suggests that Himachal Pradesh, Uttarakhand, Uttar Pradesh, Bihar, and West Bengal were the major states affected when the Ganges River water level rose (Figure 6). Due to incessant rainfall upstream, the Ganges tends to cross the danger mark in the states of Uttar Pradesh, Bihar, and West Bengal. This rise in water level across the Ganges results in flood-like situations in the neighboring districts along the river banks across the mentioned states –

Uttar Pradesh, one of the most populous states of India, experiences severe flooding during the monsoon seasons every year due to heavy inflows in the Ganges and its tributaries. Uttar Pradesh experienced severe flooding in the years 1998, 2000, 2001, 2008, and 2010.
Bihar is a particular case that gets flooded by the many overflowing rivers. With incessant rainfall at the peaks and Himalayan catchment areas, water levels rise in different rivers. Overflow of the mentioned rivers results in flooding in Bihar, especially North Bihar –
- Excess rainwater discharge from the Kosi River region in Nepal
- Incessant rainfall in Jharkhand, Madhya Pradesh, and Uttar Pradesh has resulted in increased water levels in the Sone River.
- Rising water level in river Bagmati

In July 2024, again, Uttar Pradesh experienced severe flooding affecting 16 districts and displacing over 250,000 residents. The rise in water levels of the Sharda River, the Ghaghra, the Rapti River, and the Kuwano River in Uttar Pradesh resulted in waterlogging, crop damage, and damage to houses. Approximately 1,91,515 hectares of agricultural land have been submerged in the floods, with ~923 villages impacted.

Initiatives by the Govt. of India

The Government of India has implemented various flood management initiatives since the 1954 National Flood Control Program. Key projects include the National Water Policy (2012), the National Hydrology Project for real-time flood forecasting, the Namami Ganges Program for river management, the Pradhan Mantri Krishi Sinchayee Yojana, and the National Cyclone Risk Mitigation Project (NCRMP), a comprehensive risk assessment study for 13 coastal states/UTs, resulting in the Composite Risk Atlas (CRA), a web-based tool to aid decision-makers in mitigation efforts (RMSI was commissioned for the project).

Reasons for Limited Actions and Addressing these Issues

As witnessed above, the Brahmaputra and Ganges River basins face persistent flooding challenges every year despite numerous government initiatives. The limited effectiveness of flood management actions stems from various factors, including the transboundary nature of these rivers, complex hydrology, climate change impacts, rapid urbanization, and gaps in early warning systems. Addressing these issues will require a comprehensive approach combining immediate and long-term strategies. Key solutions include:

Enhanced forecasting and early warning systems for the Ganga and Brahmaputra rivers
Natural flood mitigation through reforestation and wetland restoration along the embankments
Improved land use planning and flood-resistant construction in all flood-prone and vulnerable areas

RMSI’s Advanced Impact Forecasting Platforms

To leverage its two decades of expertise and contribution to enhance forecasting systems in the country, RMSI has developed SIREN, a global impact forecasting platform. It provides flood forecasts, a 3-day advance, and localized, multi-channel alerts.

By leveraging the state-of-the-art platform and embracing innovative solutions, the nation can build resilience against floods, safeguard vulnerable communities, and pave the way for sustainable development in these critical river basins.

Due to the sharp increase in flood risk in India over the last decade, it is imperative to develop an EWS for floods along the same lines. RMSI has worked closely with various state governments and successfully developed flood early warning systems for 17 river basins nationwide.

To make the private sector more disaster resilient, RMSI has also developed a ‘Global Disaster Impact Forecasting‘ platform that provides up to 3 days advance alerts for floods, cyclones, landslides, avalanches, lightning, fog, heatwave and coldwaves.

The success of such impact forecasting platforms can protect millions of lives and livelihoods and serve as a model for flood management in other regions facing similar challenges in the face of climate change.