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GloFAS helps Bangladesh flood forecasters to predict monsoon flood

Sazzad Hossain (University of Reading, UK, and FFWC, Bangladesh), Christel Prudhomme (ECMWF), Hannah Cloke, Liz Stephens (both University of Reading)

 

The impacts of the 2020 monsoon in Bangladesh were devastating with more than 5 million people affected by the floods, 41 casualties and tens of thousands of people living in low lying areas evacuated to flood shelters along with their cattle. During the South Asian summer monsoon, floods are a frequent natural hazard in the Brahmaputra river basin in Bangladesh, but the type of flood that happens can vary significantly depending on the monsoon rainfall and basin hydrological characteristics. Flood forecasters for the Brahmaputra consider three very important questions: when will flooding commence during the monsoon period, how long will it last and will there only be one flood or many flood waves? Predicting flood timing and duration with a sufficient lead-time is an additional challenge.

%3Cstrong%3EFlood%20impacts%20in%20Jamalpur.%3C/strong%3E%20Flood%20inundated%20house%20in%20the%20region%20affected%20by%20floods.%20(Credit:%20Flood%20volunteer%20Abdul%20Mannan)
Flood impacts in Jamalpur. Flood inundated house in the region affected by floods. (Credit: Flood volunteer Abdul Mannan)

The Global Flood Awareness System (GloFAS) is produced by ECMWF as part of the Copernicus Emergency Management Service (CEMS) and provides operational extended-range ensemble flood forecasts with a 30 day lead-time for major world river basins including the Brahmaputra in Bangladesh. The GloFAS team from the University of Reading and ECMWF are working together with the Bangladesh Flood Forecasting and Warning Centre (FFWC) and humanitarian partners to improve flood early warning in Bangladesh under the UKRI/FCDO Science for Humanitarian Emergencies and Resilience (SHEAR) research programme, so that forecasts issued to government and stakeholders are as skilful and useful as possible. GloFAS is freely available through a dedicated web interface (https://www.globalfloods.eu) or via the Copernicus Climate Data Store. GloFAS aims to provide early warning information of upcoming floods with a long lead-time to support disaster managers or national institutes for flood preparedness and response actions.

GloFAS river flow forecast.
%3Cstrong%3EGloFAS%20river%20flow%20forecast.%3C/strong%3E%20GloFAS%20forecast%20on%204%20July%202020.%20In%20the%20map%20showing%20rainfall%20levels%20over%20a%2010-day%20period,%20reporting%20points%20(triangle%20and%20circle%20symbols)%20show%20river%20points%20with%20a%20predicted%20flood%20signal.%20In%20the%20GloFAS%20forecast,%20vertical%20lines%20show%20the%20potential%20start%20and%20end%20of%20the%20flood%20event%20(source:%20GloFAS,%20www.globalfloods.eu).
GloFAS river flow forecast. GloFAS forecast on 4 July 2020. In the map showing rainfall levels over a 10-day period, reporting points (triangle and circle symbols) show river points with a predicted flood signal. In the GloFAS forecast, vertical lines show the potential start and end of the flood event (source: GloFAS, www.globalfloods.eu).

Chronology of 2020 floods

GloFAS forecasts showed a 10-day duration flood event for the end of June around 2 weeks ahead. Ten days ahead, the signal was even stronger, predicting a flood event exceeding the 20-year return period level associated with heavy rain. As predicted, the first flood wave on the Brahmaputra was observed between the 26 June and 7 July with flood levels peaking the 30 June. GloFAS also successfully predicted a second severe flood wave beginning on 11 July and reaching its peak on the 16 July (see figure). Overall, the two flood waves of the 2020 monsoon season in the Brahmaputra basin in Bangladesh lasted 35 days. GloFAS extended-range forecasts were able to predict the duration and timing of the flood waves accurately with a 10-day lead-time.

Forecast communication

For the 2020 monsoon floods, the GloFAS forecast was communicated to different stakeholders from national level to sub-national levels. National news media broadcast the risk of potential flooding as indicated by the Flood Forecasting and Warning Centre (FFWC) in Bangladesh. National and international NGOs, humanitarian agencies and development partners working in disaster response such as relief distribution have developed Forecast-based Financing (FbF) methods to help their decision making ahead of flood events. This includes the Bangladesh Red Crescent Society (BDRCS), supported by the International Federation of Red Cross and Red Crescent Societies (IFRC), and three UN agencies (FAO, WFP, UNFP). On 4 July GloFAS forecasts indicated a high probability of floods 10 days ahead, which triggered a pre-activation mode that released funds to in-country offices. Closer to the event the FFWC forecasts confirmed the imminent flooding, and cash and aid was provided to support vulnerable communities in the Bogura, Gaibandha, Kurigram, Jamalpur and Sirajganj districts, giving them the means to protect themselves and their livelihoods from the impacts of the floods.