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Hard Rain Falling: The Tropical Deluge

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Tropical storms account for two out of every three raindrops that fall on planet earth. Like melting ice caps at the North Pole, the amount of precipitation that falls near the equator is a telling early sign of global warming.

Scientists with the Tropical Rainfall Measuring Mission (TRMM), a joint venture between NASA’s Goddard Space Flight Center and the Japan Aerospace Exploration Agency, pulled together satellite data going back 27 years. Global rain is hard to measure, because most of it falls over vast expanses of open ocean. In 1997, TRMM launched a low earth orbit satellite to provide data on rainfall amounts in the tropics. What they discovered was that overall rainfall for planet earth had changed very little over the past three decades. “But in the tropics, where nearly two-thirds of all rain falls, there has been an increase of 5 per cent,” according to Guojun Gu, lead author of the study, which was published in the American Meteorological Society’s Journal of Climate.

Why is it getting wetter in the tropics? “A warming climate,” said Robert F. Adler, senior scientist at Goddard’s Laboratory for Atmospheres, “is the most plausible cause of this observed trend in tropical rainfall.” Hotter temperatures lead to greater evaporation of water from the ocean, and create conditions, which allow the atmosphere to hold more moisture. The result: more clouds, and more rain in the earth’s tropical zones.

But does an increase of 5 per cent at the equator really matter? Indeed it does. Rain is how the atmosphere of our planet “sweats.” Condensed water vapor releases heat, and this heat energy is the principle engine driving global air patterns in the lower atmosphere, where weather happens. Seasonal rainfall levels directly impact crop harvests, the breeding of livestock, the deployment of fishing boats, and the timing of construction projects, not to mention the sale of swimsuits and umbrellas.

And as we now know, such effects are not strictly local. As far back as the 1920s, British scientist Sir Gilbert Walker was already puzzling over the fact that monsoons in India had a direct effect on everything from droughts in Africa to the severity of winters in western Canada.

While the rest of the world has not seen the same increase in precipitation as the tropics, earlier computer models generated by the National Center for Atmospheric Research (NCAR) show that individual rainstorms worldwide will be heavier and more severe as global warming continues. This increase in “precipitation intensity” will be felt in the northern United States, northern Europe, and northern Asia, according to a study published in Geophysical Research Letters, a publication of the American Geophysical Union. All of these locales will experience “more intense precipitation for a given storm during this century,” researchers concluded.

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About Dirkh

  • The tropics will see and feel the inundations of global warming and glacial melting first.

    Americans may not care much about the tropical world except as resorts but here is a news flash. Where the tropics go so will the sub-tropics — Florida, Louisiana, Texas.. Then the coastal cities may feel the results of heavy rains in Belize, monsoons in India and typhoons around Borneo.

    Earth gets smaller from technology and seems shrunk by the knowledge that every piece of the ecosystem is — surprise! – systemic.

  • STM

    Explain Australia, then, where the country has been in drought – the sub-tropics especially – for the past six years.

    We could use the other moniker to explain it: Climate Change (the British have been using it after predicting another boiling summer but in fact experiencing the coldest for years).

    But in fact, in Australia, such extremes of weather – drought, flood, fire, heat – has been going on in an exndless cycle for millions of years.

  • El Nino has had particularly strong countervailing effects on Australia, according to the Tropical Rainfall Measuring Mission:

    “During El Niño, the abnormally high pressure in the West discourages any destabilizing winds while the low in the East favors storm formation; similarly, the abnormal warming of the ocean in the East feeds any weather disturbance with rain-producing evaporation while the cooling in the West reduces any moisture that is available in the air for rain to form. That is why El Niño episodes bring often DRAMATIC DROUGHTS to Australasia.”

  • STM

    The drought has partially broken, but my point is … we’re used to it, and it doesn’t seem to be any different to what we’ve had here for many generations. This isn’t the first el nino event I’ve experienced, and it won’t be the last.

    While the CSIRO says climate change may have had some role to play in the severity of the drought (although it’s not the most svere experienced, even in my lifetime), it falls short of saying that these weather events are caused by global warming. Some people have seized on a few 48C days we had last summer on the East Coast as evidence, but I can remember such days all through my life. And a 35-42C Christmas Day is not unusual in Sydney.

    At this stage, too, so far, there has been no discernible warming or cooling of tropical water temperatures in the region (around the equator, for instance, where Thailand’s water temperature in the Andaman Sea remains at 25-32C).

    And indeed, in tropical northern Australia, it’s same sh.t, different day, really. No one is noting any difference in the weather patterns.