Planning for disaster: forecasting the impact of floods in South Asia's river basins

Co-authors:
William Young, Lead Water Resources Management Specialist, the World Bank  
Thomas Hopson
Ankit Avasthi
 

The Ganges Basin in South Asia is home to some of the world’s poorest and most vulnerable communities. Annual floods during monsoon season cause widespread human suffering and economic losses. This year, torrential rains and catastrophic floods affected more than 45 million people, including 16 million children. By 2030, with ongoing climate change and socioeconomic development, floods may cost the region as much as $215 billion annually.

A new report, Flood Risk Assessment and Forecasting for the Ganges-Brahmaputra-Meghna River Basins, summarizes two recent initiatives aiming to reduce these flood losses: a flood risk assessment for the Ganges Basin and an improved flood forecasting system for the Ganges-Brahmaputra-Meghna basins.

Flooding in the Ganges Basin: What is at Risk and Where?

The new flood risk assessment provides, for the first time, a numbers-based view of the impact of floods across the Ganges Basin. Its primary purpose is to identify where flood risks are unacceptably high and where mitigation measures are required to tackle those risks — for example, by relocating levees, helping people move to lower-risk areas, improving flood forecasting and warning systems, or boosting overall economic resilience.

The assessment has information on the numbers and distribution of people at risk, as well as the value and distribution of buildings, roads, railways, and crops at risk.

An atlas provides easy-to-use risk maps and tables. For India, this information is also consolidated in a GIS-based online portal with interactive risk maps for states, districts, and blocks.

This type of information is essential to identifying flood-prone areas and then wisely planning for the use of those areas. Knowing where rivers flood and where people live, work, and travel helps decision-makers visualize the impacts of floods in different locations. That view in turn helps people to identify high-priority areas for urgent action and to design community-based strategies to minimize flood losses and capitalize on the benefits  of floods.

Legislators, for example, might use the information to seek out communities with large numbers of people at risk and provide funding to build more evacuation shelters in safe places.

Highway planners might see that roads to key hospitals are at risk and then work to elevate them.

Insurance agencies might use the data to help decide how much to charge for crop-insurance premiums.

And when torrential rains fall and floodwaters threaten, emergency personnel can use the information to target their warning messages to best help the people whose lives and property are at risk.

In short, the new Ganges flood risk assessment is a key tool for understanding and managing flood risk from many different angles.

Improved Ganges-Brahmaputra-Meghna Flood Forecasting: From Rainfall to River Flow

The new forecasting system for the Ganges-Brahmaputra-Meghna Basins provides flood forecasts for more than 85 locations. The forecasts are available online, along with near real-time data maps of rainfall (predicted and actual) and river levels.

The new system uses multiple data sets and models to improve the forecasting, up to 16 days in advance of a flood. A longer lead time before a flood gives people an opportunity to prepare : for example, farmers can harvest a threatened rice crop or move vulnerable livestock to higher ground.

The forecasts not only predict floods but also indicate the level of confidence in each forecast. Knowing whether the probability of dangerously high waters is 10 or 90 percent helps people decide what to do. 

The new system provided valuable information during this year’s severe monsoon floods, when forecasters funneled its predictions to the Red Cross and the Bangladesh Water Development Board to help with flood preparations.

The system’s cutting-edge techniques can also be incorporated into the operations of local agencies responsible for monitoring and forecasting weather and water conditions or issuing flood warnings.

Already, the states of Bihar and Uttar Pradesh in India have launched pilot projects to bring the new forecasting approaches into everyday use. India’s Central Water Commission wants to use the model for better flood forecasting in the Brahmaputra River Basin. The plan is to assess the usefulness of these upgrades in terms of the real-world currency of reduced flood risk and losses.

We hope these new tools will help regional and local decision-makers — from government officials to emergency responders to corporate leaders — to plan wisely for the many valuable uses of floodplains and to respond effectively when floodwaters threaten.