The beauty of the tropical monsoon climate

The tropical monsoon climate is found in those regions where there is a complete seasonal reversal of winds. It is mainly found beyond the equatorial region between 10° and 25° North and South of the Equator. On-shore summer winds blowing from over tropical warm oceans generate the abundant precipitation, while the off-shore winds from over land make the weather dry during winter. The most clearly defined monsoon climates are located in the coastal areas of the eastern and southern Asia. For example, India, Burma, Bangladesh, Indochina, Southern China and the Philippines experience a tropical monsoon climate.

Surface relief, direction of the coast line and the extension of the monsoon into middle-latitudes cause a number of sub-types of the monsoon climate found over this most widespread continent. Rains are abundant and intense in tropical monsoon areas. But there is a distinct dry season, though very short. However, the amount of precipitation during the rainy season is so heavy that it more than gives back the absence of rainfall for a few months. Soils retain moisture to support the plant cover. In the tropical monsoon climate summer is generally the rainy season.

During the high-sun period the on-shore winds bring a lot of moisture from over the tropical warm oceans to the land. Wherever these moisture-laden winds are forced to rise, abundant precipitation results. However, the coastal regions, if backed by highlands, receive the maximum amount of precipitation. It is important that the leeward sides of the coastal ranges suffer from the rain shadow effects. During the winter monsoon period, January and February are the driest months in South-east Asia. The distribution of rainfall in the subcontinent is more uneven than elsewhere.

The rainfall decreases from east to west and from north to south in so much so that the western and north-western regions have almost semi-arid climate. The monsoon circulation in South-east Asia is characteristically governed by the migration of ITC. Because of differential heating of the continent and the adjoining oceans, there is a complete reversal of pressure gradient over the huge landmass of South-east Asia. During winter there are centers of high pressure over the continent so that there is a flow of air towards the oceanic low pressure centers.

These winds are termed ‘the winter monsoon’ in the eastern and southern Asia. In summer, the huge landmass of Asia develops low pressure centers. These centers are reinforced by the ITC which moves suddenly to the north into the Indian subcontinent. Under these conditions the sea-to-land pressure gradients are established resulting in on-shore winds in eastern and southern Asia. These winds pick up huge quantities of moisture from the warm tropical oceans. Thus, the summer monsoons blowing from southwest Asia and eastern Asia are capable of giving heavy rains wherever conditions are favourable.

As the winter approaches, the low-pressure centers are gradually replaced by the high pressure systems. The change in precipitation is what gives this climate type its name. Precipitation only falls during the summer months, usually from May-August with June and July having the heaviest rain. The whole dry season usually has less than 4 inches of rain. During the wet season, at least 25 inches will fall. Some areas of Tropical Wet and Dry in the path of monsoon winds can receive incredible amounts of rain due to seasonal winds called monsoon.

Seasonality of its precipitation is the hallmark and most well-known characteristic of the monsoon climate. Though the annual amount of precipitation is quite similar to that of the rain forest, monsoon precipitation is concentrated into the high-sun season. Maritime equatorial and maritime tropical air masses travel from the ocean on to land during the summer, where they are uplifted by either convection or convergence of air to induce condensation. The low-sun season is characterized by a short drought season when high pressure inhibits precipitation formation.

In the case of the Asian monsoon, the replacement of the thermal low with the subsidence of the Siberian High suppresses uplift. Air masses that dominate this period are dry given their continental origin or stability. A distinct dry season from October to May, when the temperature are lower, the interior of Asia is a region of high pressure. Wind blow over the land in a north east direction , carrying little or no moisture with them. These cool , dry North East Monsoon winds blows toward areas of low pressure and do not bring rain.

A wet season from June to September, when the wind change in direction, the wind blow in the region of low pressure. Winds blow across the equator and blow over the oceans, they are warmer and carry a lot of moisture. They bring alot of rain. Total rainfall can reach 600 m The grasslands of Tropical Wet and Dry support many herbivores (plant eaters) who graze in the grasses. Most of these animals usually migrate and run in large herds for safety. Examples include wildebeests, gazelles, zebras, elephants, giraffes, etc. Many carnivores (meat eaters) follow and hunt the herbivores.

Lions, cheetahs, hyenas, and large birds hunt the savannas of Africa. In the coastal regions of the tropical monsoon climate the temperatures are uniformly warm. Air temperatures show a marked annual cycle. The highest temperatures in this climate are recorded during summer just before the arrival of rains.. Average temperatures for the summer months vary from 27° to 32°C. During winter, however, the average temperature at inland stations may vary from 10° to 26. 7°C. In higher latitudes the drop in the minimum temperatures is large. During the wet seasons, there is extensive cloud cover.

This blocks most of the incoming solar radiation during the day, and traps the outgoing radiation at night. Thus, the diurnal temperature range is small. Range of temperature in the tropical monsoon climate is a bit larger than that in the equatorial climate. The annual range registers a variation ranging from 2°C to 11°C. The diurnal range in the coastal regions is less than what it is in the continental interiors. Another characteristic feature of the diurnal range of temperature is that it is considerably higher in the dry summer months than in any other part of the year.

The monsoon circulation in South-east Asia is characteristically governed by the migration of ITC. Because of differential heating of the continent and the adjoining oceans, there is a complete reversal of pressure gradient over the huge landmass of South-east Asia. During winter there are centers of high pressure over the continent so that there is an outflow of air towards the oceanic low pressure centers. These winds are termed ‘the winter monsoon’ or the ‘dry monsoon’ in the eastern and southern Asia. In summer the huge landmass of Asia develops low pressure centers.

These centers are reinforced by the ITC which moves suddenly to the north into the Indian subcontinent to 20° or 25° N latitude. Under these conditions the sea-to-land pressure gradients are established resulting in on-shore winds in eastern and southern Asia. These winds pick up huge quantities of moisture from the warm tropical oceans. Thus, the summer monsoons blowing from southwest in the southern Asia and southeast in eastern Asia are capable of giving heavy rains wherever conditions are favourable. As the winter approaches, the low-pressure centers are gradually replaced by the high pressure systems.

In fact, the so-called winter monsoons are nothing but the re-establishment of the northeast trades which are dry except in those areas where they reach after passing over the sea. Rains are abundant and intense in tropical monsoon areas. But there is a distinct dry season, though very short. However, the amount of precipitation during the rainy season is so heavy that it more than gives back the absence of rainfall for a few months. Soils retain moisture to support the plant cover. In the tropical monsoon climate summer is generally the rainy season.

During the high-sun period the on-shore winds bring a lot of moisture from over the tropical warm oceans to the land. Wherever these moisture-laden winds are forced to rise, abundant precipitation results. However, the coastal regions, if backed by highlands, receive the maximum amount of precipitation. It is important that the leeward sides of the coastal ranges suffer from the rain shadow effects. During the winter monsoon period, January and February are the driest months in South-east Asia. The distribution of rainfall in the subcontinent is more uneven than elsewhere.

The rainfall decreases from east to west and from north to south in so much so that the western and north-western regions have almost semi-arid climate. In the tropical monsoon climate, the amount and distribution of precipitation determine, to a large extent, the type of natural vegetation. Towards the equator-ward margins, where the precipitation is heavy, the tropical monsoon forest resembles the tropical rainforest. However, because of the seasonality of rainfall, species are limited in the monsoon forests. Towards the drier margins, rainforests are replaced by more sparse jungles, thorn forests and savanna grasslands.

In India, for example, there are different types of natural vegetation ranging from the tropical rain-forests of the Malabar and Assam to the deciduous forests of the areas with moderate rainfall to thorny bushes of the more arid regions with scanty rainfall. Teak is the most valuable timber, and it is found in Burma and certain other parts of India. Besides, shisham, sal, mahua, mango tree, jamun, neem, and many more species of trees are found in the deciduous forests which shed their leaves before the commencement of the long dry season in order to conserve moisture.

In fact, the deciduous trees of the monsoon forest are a fine illustration of their adaptability to a wet-dry climate in which rainy season with adequate water surplus alternates with a dry season with soil-water deficit. These forests are generally more open than the tropical rainforests. The trees are less tall and the branching starts at a lower level. Tree species may vary from 30 to 40 in a small area. Trees have thick and rough barks as moisture conserving device. Tree tops are fairly large and round. Outside India, the typical monsoon forest is found in Burma, Thailand and Cambodia.

In West Africa and in Central and South America there are large areas of deciduous monsoon forest bordering the equatorial rain forests? In more humid areas wherethe forestis dense, the flying and climbing species of the animal life of the equatorial forest are dominant. But in drier regions where the trees are widely spaced with grasslands, large animals constitute the animal kingdom. Some of these animals are carnivores, while others are herbivores, such as, tigers, lions, leopards, wolves and jackals, elephants, wild buffalo, rhinoceros, deer, and antelopes.