A monsoon is often associated with heavy rains, a hurricane, or a typhoon. This is not entirely true: the monsoon is not just a storm, it is rather a seasonal movement of wind over an area. As a result, there may be heavy summer rains and drought at other times of the year.
The monsoon (from the Arabic mawsim, meaning “season”) is due to the temperature difference between land and ocean, the National Weather Service explains. The sun warms the land and water differently, and the air begins to “tug of war” and wins over the colder, moister air from the ocean. At the end of the monsoon period, the winds turn back.
The wet monsoons usually come in the summer months (April to September) bringing heavy rains. On average, about 75% of annual rainfall in India and about 50% in the North American region (according to a NOAA study) falls during the summer monsoon season. As mentioned above, wet monsoons bring ocean winds to land.
Dry monsoons occur in October-April. Dry air masses come to India from Mongolia and northwest China. They are more powerful than their summer counterparts. Edward Guinan, professor of astronomy and meteorology, states that the winter monsoon begins when “the land cools faster than water and high pressure builds up over the land, forcing ocean air out.” The drought is coming.
Every year the monsoons behave differently, bringing either light or heavy rains, as well as winds of various speeds. The Indian Institute of Tropical Meteorology has compiled data showing India’s annual monsoons over the past 145 years. The intensity of the monsoons, it turns out, varies over 30-40 years. Long-term observations show that there are periods with weak rains, one of these began in 1970, and there are heavy ones. Current records for 2016 showed that from June 1 to September 30, precipitation amounted to 97,3% of the seasonal norm.
The heaviest rains were observed in Cherrapunji, Meghalaya state in India, between 1860 and 1861, when 26 mm of rain fell in the region. The area with the highest average annual total (observations were made over 470 years) is also in the state of Meghalaya, where an average of 10 mm of precipitation fell.
The places where the monsoons occur are the tropics (from 0 to 23,5 degrees north and south latitude) and the subtropics (between 23,5 and 35 degrees north and south latitude). The strongest monsoons are observed, as a rule, in India and South Asia, Australia and Malaysia. Monsoons are found in the southern regions of North America, in Central America, the northern regions of South America, and also in West Africa.
Monsoons play a decisive role in many areas of the globe. Agriculture in countries like India is heavily dependent on the rainy season. According to National Geographic, hydroelectric power plants also schedule their operation depending on the monsoon season.
When the world’s monsoons are limited to light rainfall, crops don’t get enough moisture and farm incomes decline. Electricity generation is declining, which is only enough for the needs of large enterprises, electricity becomes more expensive and becomes inaccessible to poor families. Due to the lack of own food products, imports from other countries are increasing.
During heavy rains, floods are possible, causing damage not only to crops, but also to people and animals. Excess rains contribute to the spread of infections: cholera, malaria, as well as stomach and eye diseases. Many of these infections are spread by water, and overburdened water facilities are not up to the task of treating water for drinking and household needs.
The North American monsoon system is also causing the start of the fire season in the southwestern United States and northern Mexico, the NOAA report says, due to an increase in lightning caused by changes in pressure and temperature. In some regions, tens of thousands of lightning strikes are observed overnight, causing fires, power failures and severe injuries to people.
A group of scientists from Malaysia warns that due to global warming, an increase in precipitation during the summer monsoons should be expected in the next 50-100 years. Greenhouse gases, such as carbon dioxide, help trap even more moisture in the air, which rains down on already flooded areas. During the dry monsoon season, the land will dry out more due to the increase in air temperature.
On a small time scale, precipitation during the summer monsoon can change due to air pollution. El Niño (temperature fluctuations on the surface of the Pacific Ocean) also affects the Indian monsoon both in the short and long term, say researchers from the University of Colorado at Boulder.
Many factors can influence the monsoons. Scientists are doing their best to predict future rains and winds – the more we know about the behavior of the monsoon, the sooner preparatory work will begin.
When about half of India’s population is employed in agriculture and agronomy accounts for roughly 18% of India’s GDP, the timing of the monsoon and rainfall can be very difficult. But, research conducted by scientists can translate this problem into its solution.