Public Release: 

New monsoon forecasting method could increase crop yields

Georgia Institute of Technology Research News

A recently devised method for forecasting monsoon-season weather in Bangladesh could improve agricultural production in south Asia and equatorial Africa, according to a climate researcher at the Georgia Institute of Technology.

The new technique produced 20- to 25-day forecasts of rainfall in the 1-million-square-kilometer Ganges Valley of Bangladesh during the summer of 2002. The forecast closely mirrored actual precipitation for the season, according to U.S. State Department-funded research led by Professor Peter Webster and his students in Georgia Tech's School of Earth and Atmospheric Sciences. In the future, such forecasts could guide farmers in choosing optimal planting times and making other decisions, such as better water management, that affect crop production, Webster said.

He presented his findings Feb. 17 at the 2003 meeting of the American Association for the Advancement of Science (AAAS) in Denver. "Forecasting weather a few days in advance is not particularly useful for agriculture," Webster said. "What is needed is a 20- to 25-day forecast.... We are able to do that with our new method. We could have predicted the month-long break in the monsoon rains that lasted from the end of June to early July and which caused a $6 billion loss in crops in the Ganges Valley. If farmers had this forecast last summer, they could have changed agricultural practices, such as delaying the planting."

Webster's forecasting method is applicable to the rainy season of any monsoon region and adjusts for precipitation changes related to temporary climatic events such as El Niño and La Niña. Last year was an El Niño year, and, as expected, it resulted in decreased rainfall on the Indian subcontinent.

The method -- developed with graduate researcher Carlos Hoyos of Colombia -- is essentially statistical, but depends on a detailed knowledge of the dynamics of the atmosphere and the ocean, which produce monsoon variability on monthly time scales. Many years of theoretical modeling and experimental research in the Indian Ocean have given researchers an understanding of the physical nature of the oscillation. Meanwhile, much of what researchers understand about the nature of the variability comes from a research cruise Webster led in the Bay of Bengal in 1999.

Webster is now intent on making this type of forecast - and a future version for flood prediction - available to agricultural and other government officials in Bangladesh and, later, other places where rainfall varies drastically within a season. He has received official government recognition to form an organization called Climate Forecasting Applications in Bangladesh (CFAB). With this group's help, Webster hopes to significantly improve crop yields.

"This 20- to 25-day forecast has the potential for creating a new green revolution," Webster said. "We had the first one in the '60s with hybrid crops that increased yields by 30 to 40 percent, but it was quite expensive as the new hybrid crops demanded the use of large amounts of pesticides and fertilizer. And there was a lot of pollution associated with this use.... Our forecasting scheme could create a truly green revolution. It won't require any new pesticides or fertilizers and may reduce their use by application when they are most needed. Also, water managers could hold water in reserve for dissemination later."

Webster has another, more problematic goal for his research. He hopes, in time, that farmers in developing countries will become less dependent on having their children as co-laborers in the fields. Perhaps they will choose to have smaller families if they see their crop yields increase and gain confidence in the new forecasting technique, Webster said. Such choices could ease environmental, political and societal pressures related to large, dense populations in developing nations, he added. The monsoon regions are already home to more than 50 percent of the world's population and are growing at rates of 2 to 4 percent a year.

"It is our aim to reduce vulnerability to climate variability through this long-term forecasting," Webster said. "These issues are tied together. You won't be able to do anything about population growth until you decouple it with the need for a large population." Webster presented his views, along with his research, in his AAAS talk titled "Monsoons in a Warming World: Racing with the Four Horsemen." In a presentation he prepared with his son, Benjamin Webster, an environmental policy researcher at Georgetown University, the professor asserted that four issues affecting developing nations are inextricably intertwined and must be addressed as a whole, rather than in a piecemeal fashion. Those issues are:

  • uncertainty in the changes in monsoon climate stemming from global warming;
  • uncertainty in the form and influence of natural climate variability - such as that caused by El Niño -- on the monsoon regions;
  • population growth and its associated increases in communicable diseases, demand for food, and the increased scarcity of arable land and fresh water; and
  • uncertainty in political and societal decision-making relative to changing circumstances.

"You can't untangle the social impacts of these issues from the scientific impacts," Webster said. "Simple policies like, 'We can fix one issue piecemeal and then move on to the next problem,' don't work. You have to grasp the entirety of the problems and address them simultaneously. The prospect is very daunting, but not to do so may be catastrophic. "

In his talk, Webster suggested what he calls new methods of addressing policy that span all four elements of uncertainty about the monsoon in a warming world. These strategies are based on risk assessment and their belief that industrialized nations should not impose First World views on Third World countries, Webster added.

"In developing countries, one is faced with having to make a yes or no decision," Webster said. "Do I plant or do I not plant? Do I harvest or do I wait? What we try to do is provide the best information for a person making what may be a life or death decision. We provide a forecast with a probability. For example, there is a 40 percent chance of a moderate flood and a 10 percent chance of a devastating flood. The user of the forecast can then make an informed decision and can judge the cost of an action versus the loss of what might be a remote outcome. This approach can be extended to decision-making relative to all of the four uncertainties. This nested probabilistic approach offers some hope of assessing the overall vulnerability in a warming world and may lead to meaningful decisions being made."


For technical information, contact:
Peter Webster, 404-894-1748 or

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