Extreme Weather in the Tropics: Extremely Confounding

by Eric Ellman

The question of why it rains, when and where it rains in the tropics is one of the remaining mysteries of earth science, says Yale Assistant Professor Bill Boos.  In equatorial regions, the Coriolis effect – responsible for the cyclonic whirl of a hurricane – is largely absent, leaving more amorphous forces like latent heat – the energy produced when water vapor condenses into water droplets – to organize large-scale weather patterns there.  Enormous quantities of water evaporating and condensing are the driving force behind continental scale monsoons that affect the livelihoods of billions of people, but which are little understood. 

“A hotter globe means we’ll be dumping more water in the atmosphere,” muses Boos, suggesting a future where more rain falls from the continental scale weather patterns he studied at MIT and Harvard, and which he now researches at Yale.  With support from the Yale Climate and Energy Institute, Boos convenes a rare two-day workshop this April 17-18 where 30 monsoon experts from Asia, Africa, Australia and North America will help bridge the difference between what is understood about cyclonic storms like hurricanes and typhoons, and what is known and can be predicted about monsoons.

That knowledge gap is an accident of geography and wealth. Nations in the mid-latitudes can afford more weather stations and assigning people to track hurricanes and cyclones. With notable exceptions like Australia, countries impacted by monsoons do not record weather with the same rigor, says Boos. As a consequence scientists are less knowledgeable about how monsoon occurrence, strength and duration has changed over time, and are that much more challenged to predict how it will vary in the future. 

For farmers in nations like India, where rain-fed agriculture is widespread, knowing when the monsoon begins is critical.  The current predictive capacity of 3 to 5 days gives farmers little chance to consider when to plant, how much of their seed to plant, and whether or not to purchase crop insurance against the chance they’ve chosen poorly.

The vast number of people affected by monsoon rains in the world’s second most populous nation has drawn the attention of economists working under Yale economist Robert Mendehsohn.  Their interest is the comparative benefit of investments in crop insurance vs. what it would cost to increase predictive abilities and adjust planting and harvesting accordingly.