Monsoons What Is a Monsoon?

Monsoons

What is a monsoon? The major weather disturbance known as a "monsoon" is actually in reference to a seasonal wind shift, not necessarily a brooding storm pattern, although most people think of "monsoon" as a huge hurricane-like event that usually is reported in Asia. Textbook authors McKnight and Hess explain in Physical Geography how monsoons occur. A monsoon (from the Arabic word "mausim" which simply means "season") occurs when trade winds reverse; in summer when there is a flow of wind from the ocean to land ("onshore flow"); and a monsoon can occur during winter months when winds are flowing from land to the ocean ("offshore flow"). In the summer, where there is a low-pressure center over a landmass, that warm air attracts the cooler moist air over the ocean, and draws it in, McKnight goes on. Cool air is always drawn to warm air, and when the cool air also happens to be moist, it causes precipitation, and sometimes too much at one time.

Why are monsoons important to study? This is important for weather scientists to study, McKnight asserts, because "More than half of the world's population" lives in regions that have frequent monsoons roaring onshore. The rains that monsoons produce are vital in Asia, for example, for the production of foods (such as rice and corn). In south Asia, monsoons hit most often in the summer, and they are a double-edged sword, because they bring moisture to the region, important for cash crops and for citizen survival; but they also bring damaging winds and floods, which costs lives and money.

In August 2006, for example, a monsoon blew out of the Indian Ocean and into Pakistan and killed 192 people while damaging 18,000 houses, according to Xinhua News Agency. Over 190 people were also injured in the monsoon. Flooding in the provincial capital of Peshawar, Pakistan, damaged 8,407 houses and left 51 people dead.

One of the emergencies that goes along with a monsoon's flooding is the need to set up "mass vaccination" shelters to help prevent communicable diseases; flooding brings impurities, dead animals and toxic substances into the homes and on the streets of communities and diseases such as typhoid and tetanus can harm large numbers of people. The Xinhua News Agency explains that the heavy rains from monsoons occur between the period from the beginning of July through September.

Meanwhile, the journal Science News published an article in 2002 that reports, "Asian monsoons have been intensifying over the last 400 years." Reportedly, they are expected to continue to become more intense, causing "severe flooding and erosion" that may in some cases affect up to "half the world's population." Monsoon storms carry important quantities of rain to "billions of people in India, China, Bangladesh" and other Asian countries. As was mentioned earlier, when trade winds "reverse direction" they carry very moist air inland where it is very hot and dry.

Gerald a. Meehi works with the National Center for Atmospheric Research group in Boulder, Colorado; he remarks in Science News that the "South Asian monsoon...is key to agriculture and water resources." Hence, the past and future behavior of the monsoon "is...of critical interest." How do scientists know what monsoons have done in the past? David M. Anderson at the University of Colorado in Boulder has some answers; he and his colleagues have examined microscopic "hard-shelled foraminifer Globigerina bulloides (fossils) in sediments in the Arabian Sea," the article goes on.

By examining these fossil records researchers can better understand variations in the strength of monsoons over the past hundreds of years. What happens is that winds blow along the coasts of Saudi Arabia and Oman, Anderson explains; these winds "churn up deep waters and transport minerals to the otherwise nutrient-poor surface waters." When the winds from the monsoons are strong, those shallow-living G. bulloides experience a population explosion and as a result, "abundant shells end up in sediments below." Anderson and his team took a sediment sample from under the Arabian Sea that was 100-millimeter deep, called a core. They then separated the core, according to Science News, into 2-mm layers. Those 2-mm layers were carbon-dated (a very accurate way of telling how long a substance has been in the ground) and carefully examined for G. bulloides.

As a result of this research, the team was able to check the intensity of monsoons for as far back as 1,000 years. And what did they discover regarding monsoons over the past one thousand years? There was a "low in monsoon wind intensity" around the year 1,600, the article reports, but since then there has been "a steady increase." And moreover, the abundance of G. bulloides shows the scientists that there has been "a more marked increase in monsoon during the past 100 years.

Researchers attribute the rise in wind intensity from monsoons over the past 100 years to global warming. The reason scientists involved with this research feel sure that global warming is causing the more intense monsoon winds because in Asia, global warming may create "a greater summertime disparity between land and ocean temperatures," according to Anderson. As a result of this contrast in temperatures, monsoon intensity logically will rise. "This study provides additional evidence of anthropogenic climate change," said Meehi. But this is not all bad news, since higher intensity of monsoon winds "might mean fewer crop failures" in Asia. But along with that possible positive note, the increased intensity of monsoons (wind and rain) could also cause flooding and erosion that could negatively affect the livelihood "of millions."

Another interesting side note of monsoons in Asia - published in the New Scientist magazine - occurred in August 2007, as political leaders in Nepal blamed India for floods in Nepal's low-lying region called Terai. This low-lying area was under water following intense monsoon rains, because, according to the Nepalese foreign ministry, India has built dams along the border with Nepal. Those dams cause the water to back up dramatically when heavy rains fall, and some of the dams are not legal, according to the story in New Scientist. The rivers that are dammed up are tributaries of the main Indian River, Ganges, which has as its source the Himalayas.