Comparison of La Niña Impacts in Australia and in South Asia


As Australia is a fairly prosperous ‘first world’ country we are lucky to be able to withstand and survive La Niña and El Niño events without extreme loss of human life and loss of lifestyle.  Unfortunately other countries around the world are not so lucky. The country of Bangladesh located in the north east of the Indian subcontinent for example is one of the most flood-prone countries in the world (see Figure 1). It is also one of the poorest with a population least able to respond effectively to the ravages of environmental disasters.

Figure 1:  Regional map of South Asia showing the location of Bangladesh and Burma (Myanmar)

During the La Niña years of 1954 and 1955, when Australia experienced the tragic Hunter River floods, Bangladesh also experienced two consecutive years of devastating flooding. In the wake of those particular years the United Nations for the first time initiated a major investigative mission to look into the problems of flood in this country and to suggest long-term remedial measures.

The 1988 flood was another event which occurred in an El Niño season as did ‘the flood of the century’ in 1998 which began at the tail end of an El Niño but reached its peak in the second half of the year when the rising positive values of the SOI indicated a typical La Niña episode which continued into the middle of 1999. Nevertheless, the association between La Niña and flooding in Bangladesh is by no means a consistent pattern. The floods of 1987 for example took place in an El Niño year when SOI values were continually in the negative.

The impacts of cyclonic weather events in Bangladesh can be massive in scale. In some of the worst events of the past, the death toll has risen to hundreds of thousands. Often a major contributor to these deaths has been starvation after large scale loss of agricultural production. Fortunately, in recent years, such as in the terrible floods of 1998, national and international efforts have been able to head off the worst effects of loss of crop production.

On the other hand, the extent of environmental destruction caused by these floods seems to a have worsened in recent years. It seems hard to believe, but in some floods in the last half century more than half the entire land mass of the country has been affected causing damage in the order of billions of dollars. Based on the historic records, it seems that the frequency, magnitude, and duration of floods have increased substantially during the last few decades.  The total area covered by major floods has been steadily increasing since 1974, with an exception of the 1984 floods. The area affected by major floods has increased from 35% in 1974 to an amazing 68% in 1998.

Damage on this scale arises from the unfortunate conjunction of three facts of geography:

  • a humid tropical environment;
  • three major river systems covering a combined total catchment area of about 1.7 million sq. km arise in the Himalayas and funnel down to the sea through Bangladesh;
  • much of the flood prone delta area is flat and only a few metres above sea level.

In recent years these geographic circumstances have been exacerbated by negative impacts (e.g. forest clearing, urbanisation) on the natural water ways due to rising human populations.

One last point needs to be made: flooding is mostly a welcome event in the Bangladeshi annual calendar. Yearly floods on a modest scale, associated with a typical year (i.e. non - La Niña / non - El Niño year) are essential for the rejuvenation of soil moisture and fertility of the traditional cropping lands of the Bangladesh delta.

On those infrequent occasions in the past when the annual rains and the welcome floods have failed altogether, the consequences for the Bangladeshi people have been even more devastating than the historic flood events. A historical analysis of Bangladeshi monsoon rainfall patterns has shown that in general there is a decrease in rainfall in El Niño years in all the seasons - the pre-monsoon, the monsoon and the post-monsoon. It has been determined that the great Bengal famine year of 1770 - when about  10 million people,  one third of the total human population, lost their lives - was a classic El Niño year. Another great famine in Bengal, the 1913 famine, also took place in an El Niño year.


During May 2008,  Burma (officially known as Myanmar) was struck by  Cyclone Nargis, a Category 3 or minimal Category 4 hurricane (with sustained winds of 130 mph and gusts of 150-160 mph ), producing devastating  floods that were probably the worst ever in the recorded history of that country.

Figure 2: Cyclone Nargis as seen from NASA’s Terra satellite on May 2, 2008
(Source: NASA Earth Observatory )

By mid June 2008 it had been estimated that at least 138,000 people were either killed or missing. Damage has been estimated at over $10 billion (USD).

Figure 3: Satellite photos from NASA's Terra satellite, showing part of Burma (Myanmar) on April 15, 2008 (top) and May 5, 2008 (bottom), resulting in before-and-after comparisons of the impact from Cyclone Nargis  (Source: NASA Earth Observatory)