Seasonal flood forecast

For any type of response planning (i.e., relief operation at the government level and crop plantation at the individual level), there is a demand for long-range (month to season) flood forecasts. The seasonal forecast is a type of long-range forecast. Seasonal forecasting is the outcome of a shift from deterministic predictions (e.g., 0.2 mm of rain will fall tomorrow) to probabilistic forecasting schemes. Here the emphasis is on forecasting the probability that a particular climate variable will be significantly above or below a mean state over a time-averaged period (usually ranging from a month to a season) (e.g., there is a 20% probability that the seasonal flooding in the northern part of Bangladesh will be higher than normal).

Approaches to seasonal forecasting can broadly be divided into two categories: empirical/statistical techniques, and numerical/dynamical modeling, of which the former have historically been more widely developed. Unfortunately, research in Bangladesh relating to seasonal flooding has just begun. Dr. Md. Rashed Chowdhury, a Bangladeshi scientist, who has been working to develop seasonal forecasting schemes for Bangladesh has emphasised that Bangladesh can be benefited by using simple statistical methodology to develop seasonal flood forecasts. Based on the global mean atmospheric response to different large-scale modes of oceanic variability, (e.g., El Nino-Southern Oscillation (ENSO) and associated teleconnections), it may then be possible to predict how the flooding in Bangladesh will respond to certain oceanic situations from the knowledge of how the atmosphere (here Bangladesh flooding) has responded in the past to the variation of sea-surface temperature (SST) in the tropical Pacific Ocean, with a variety of lag times. Dr. Chowdhury, from his several years of research experience in the International Research Institute for Climate Prediction (IRI) of the Columbia University (USA), concluded that the seasonal flood prediction in Bangladesh is possible from the unusually warm or cold SST in parts of the tropics. This predictability can be enhanced with the information achievable from monitoring the downstream stream-flows -- that are generated mainly from upstream rainfall conditions -- in advance of the flooding season.

By and large, the demand for seasonal forecasts is significantly rising both in the national and local levels. The justification for seasonal to inter-annual forecasting in Bangladesh has already been established in a 'needs analysis for forecasting tools and means' by the Environment and Geographical Information Services (EGIS) support. However, the success of seasonal forecast, in contrast to short-term prediction, depends on consensus among the participating institutions followed by effective dissemination through the appropriate channels, which demands the enhancement of the existing Flood Forecasting and Warning Response System (FFWRS) again. A 5-stage FFWRS -- i) Flood forecasting, ii) Forecast interpretation and message formulation, iii) Warning preparation and dissemination, iv) Responses, and v) Review and analysis -- has been proposed by Dr. Chowdhury also stressing the need of consensus forecast, a framework similar to that of the 'Southern African Regional Climate Outlook Forum' (SARCOF), and emphasising the need for a climate 'Outlook Fora' for a comprehensive and participatory approach to seasonal flood hazard management in Bangladesh.