Consequent flooding

Over the past several months most of the statistical and coupled model forecasts have tended towards cooler conditions in the tropical Pacific through mid-2006. The spread of the most recent statistical and coupled model forecasts (weak La Niña to ENSO-neutral) indicates some uncertainty in the outlooks. However, current conditions (stronger-than-average easterly winds over the central equatorial Pacific) and recent cooling trends in observed oceanic conditions support continuation of La Nina conditions in the tropical Pacific during the next 3-6 months.

What climatic impact can this La Nina have in Bangladesh?
Scientific views about this stronger-than-average easterly winds over the central equatorial Pacific) and the decreasing SST anomalies throughout the central and eastern equatorial Pacific) and teleconnections with climate anomalies in Bangladesh have been explained by Walker during the 1920s. According to his observations, lower than average atmospheric pressure prevails in the region from Australia to India when higher than average atmospheric pressure prevails in the eastern tropical Pacific Ocean. The scientific reason is that air flows from high-pressure regions to low-pressure ones. As a result, a huge volume of moisture propagates from the Pacific Ocean to Bangladesh and India; due to the prevailing low atmospheric pressure in this area at that time, the moisture-laden air rises, causing heavy rainfall in Bangladesh and India. Several scientific researches have identified that during La Niña years (either strong or moderate strength) Bangladesh is often a victim of flooding (e.g., 1984, 1988, and1998).

Right now, it looks like a weak La Niña is developing, which may cause a slight enhanced rainfall during the next monsoon season. But if the La Niña condition continues to develop and gain further strength (like moderate or strong in nature) then more rainfall along the Ganges-Brahmaputra-Meghna basins is likely, which might cause a basin-wide flooding. Usually, ENSO starts to develop in summer, reaches its peak phase in the following winter, and gradually weakens through the spring. Therefore, we have to wait until April-May of 2006 to see the maturity stage of this La Niña for any conclusive statement on the strength of La Niña and seasonal flooding (2006) in Bangladesh.

Dr. Rashed Chowdhury is the Research Scientist (Faculty) of the Pacific ENSO Applications Centre (PEAC), University of Hawaii, USA; Email: rashed@hawaii.edu