Development of Flood Forecasting for the Ganges and the Brahmaputra Basins using satellite based precipitation, ensemble weather forecasts, and remotely-sensed river widths and height Satya Priya, World Bank Tom Hopson, NCAR (among others) Charon Birkett, Univ. of Maryland Robert Brakenridge, Dartmouth Flood Observatory

Project Objectives % Objective 1 Objective 2 Assess the usefulness of the key data sources for predicting river flooding for India – what are their errors, when do they show skill (e.g. satellite altimetry, remotely-sensed river “width” measurement, ensemble precipitation forecast, etc.) -- make these data sets available for other practitioners. Objective 2 Show “proof of concept” operational real-time flood forecasts at sites throughout the Ganges and Brahmaputra – integrate these data sets into a common framework for flood forecasting, showing how this can be achieved from an “engineering perspective”, but also provide operational forecasts with potential for societal benefit Objective 3 Provide effective forecasting displays, including precipitation and maps of areas of inundation corresponding to forecasted discharge that have potential benefits for “on the ground” operations and decision-making Objective 4 Determine the overall flood forecasting skill of the system, and provide recommendations on where future resources should be allocated to further extend the “forecast horizon” to meet World Bank development goals %

Example of Objective 1: skill of key data sources Satellite Altimetry: observed good precision (e.g. 10cm) of JASON II instrument over channels high up in the river catchments (only 100s of meters in width), with good potential to detect upstream flood waves. However, the gap in time between repeat measurements means that this instrument needs to be used in conjunction with other data sources.

Example of Objective 2: “proof of concept” operational real-time flood forecasts Forecasts based on upstream gage measurements (as shown below for one site in the lower Ganges), can alone provide advanced flood warning information, but required timely and easily-accessible data sharing protocols

Example of Objective 3: effective forecast displays Forecasting severe rainfall events in a river basin can warn of local flash flood risk. Shown below is a real-time display of ECMWF 24hr in-advance rainfall amounts at medium (thick blue) to small (thin blue) basins for last summer in the Ganges.

Example of Objective 4: forecasting skill of the system and areas of improvement At short lead-times, the past record of river stage along can be helpful. However, depending on the size of the watershed, beyond 3 days ensemble rainfall forecasts become important, as seen below comparing the ensemble spread in 1-day and 3-day gage-only forecasts in the lower Brahmaputra. 1-Day Lead-Time 3-Day Lead-Time Site: 005-LBDJPG

“I have a very strong feeling that science exists to serve human welfare. It’s wonderful to have the opportunity given us by society to do basic research, but in return, we have a very important moral responsibility to apply that research to benefiting humanity.” Dr. Walter Orr Roberts (NCAR founder) “I have a very strong feeling that science exists to serve human welfare. It’s wonderful to have the opportunity given us by society to do basic research, but in return, we have a very important moral responsibility to apply that research to benefiting humanity.” Walter Orr Roberts