The Summer Monsoon lasts for 4 months. Intense solar heating leads to scorching temperatures over the Asian landmass. As hot air expands and rises upwards, a semi-permanent low-pressure area develops. As this warm air rises, cooler air from the sea moves in to replace it bringing with it the very moist air that causes the exceptionally high rainfall (convectional and orthographic) associated with monsoons, along with the fact tat the ITCZ has moved north. Moist southeasterlies originating from the southern Indian Ocean and the Indonesian-Australian region transforms into southwesterlies on crossing the equator and flow across Southeast Asia before converging towards India, China and Northwest Pacific, due to the Coriolis effect. The reason the Monsoon is maintained is that latent heat is released.
The distinguishing characteristics of monsoons are temperature and precipitation. Like in the tropical rainforest climate, temperatures remain high all year in the monsoon climate. As shown in the climograph for Mangalore, (Figure 2), the average annual temperature is 27.05 oC, though having an annual temperature range of 3.6oC. The monsoon climate's temperature range is somewhat similar to that of the rainforest, but it exhibits a slight different temporal pattern. In the rainforest we noted two periods of maximum temperature in association with the "migration" of the Sun's vertical rays. The monsoon climate tends to have its highest temperature just before rainy period. Once the rainy period starts, clouds block incoming solar radiation to reduce monthly temperatures.
Figure 1 Comparison of monthly temperature in the
rain forest (Iquitos) and monsoon climates (Mangalore).
Seasonality of its precipitation is the most well-known characteristic of the monsoon climate. Though the annual amount of precipitation is quite similar to that of the rainforest, 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. Locally, orographic uplift is an important mechanism for promoting precipitation. As air travels into the Indian subcontinent, it is uplifted by the Himalayas, causing cloud development and precipitation. The low-sun season is characterized by 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 give their continental origin (cT,cP) or stability (mTs).
Figure 2 Climograph for
Mangalore, India
Lat/Long = 12.53o N, 74.52o E
Average Annual Temperature (oC) = 27.05
Annual Temperature Range (oC) = 3.6
Total Annual Precipitation (mm) = 3409.2
Summer Precipitation (mm) = 3115.9
Winter Precipitation (mm) = 293.3
Monsoons have both benefits and problems. Floods are a normal occurrence for the people of south Asia. Every year, floods destroy crops and displace the region's inhabitants. Floods are most common in the low lands of Bangladesh where the Ganges and Brahmaputra rivers meet. Floods are both a hazard and an asset. While the floods are drowning crops and livestock, and damaging property, they are also fertilising the soil in the form of silt. The floods caused by the monsoon produce lake areas where fish breed -fish is an important part of the local peoples diet as it provides protein. The saturated soils produced increase dry season yield later in the year, when very little water is available. The percolating floodwaters also recharge water tables and raise well levels, which help to store water for the dry season. For example the southwest monsoon in India is critical to the development of Indian agricultural production. The monsoon provides 80% of India’s total precipitation and is critical to the development of its major food and commercial crops such as rice, coarse grains, pulses, peanuts, soybeans and cotton. Planting of the largely rainfed kharif (monsoon season) crops, which include rice, sorghum, corn, millet, soybean and cotton beins after the monsoon begins and planting will continue through July and August. Therefore the country’s economy is largely dependant on the monsoon.
However, the monsoon also brings problems, as it is unreliable and rainfall amounts vary. A very heavy monsoon can cause problems such as swollen rivers and saturated soils leading to severe flooding and landslides, and in areas like low-lying Bangladesh floodwater can be fatal. Flooding can also lead to polluted water supplies, which cause disease to spread. Flooding destroys local irrigation schemes so in the dry season crops cannot be watered sufficiently, and fields of crops are washed away, along with roads and bridges. On August 14, 200, hundreds of people were killed by floods and landslides forms the high mountains of Bhutan and Nepal to the lowlands of Cambodia and Bangladesh. In Bhutan water supply’s broke down, roads were blocked due to landslides and erosion, and over a thousand people were made homeless and had to live in temporary shelters. In Nepal 98 people were killed and 948 houses were destroyed, and in India over 30 people were killed, 4-5million people made homeless, hundreds of thousands of people trapped on elevated areas of land, where they were easy prey for water borne diseases.
Of all natural disasters, drought is by far the most feared. When the rains do not come, crops are not planted and food supplies dwindle. If there is a lack of continued showers or breaks in the rain, plant seedlings may not survive. As the crops grow, later breaks or insufficient rainfall may limit the number and size of maturing plants. If the rains are too hard, young plants and seedlings can be washed away. The effects of which can be devastating. Also if the monsoon fails problems occur: metropolitan cities can be without adequate water supplies; train loads of water may have to be dispatched from areas where is rainfall; and agriculture crops fail due to lack of water. Between 1899-1901, about 15% of the population of Gujarat in western India died from famine. Estimates of 10 million in Bengal in a famine in 1770, 800,00 in UP in 1836, and one million in Orissa in 1865-66 are just a few examples of the damage drought can have. These periods all have in common one thing, the failure of the rains, which is the first link in the chain that leads to famine. While the people of Monsoon Asia lived in drought prone areas for hundreds of years, it is only during the last 25 years that methods have been developed to safeguard against famines.
Atmospheric processes are responsible for the tropical monsoon climate, and influence humans’ lives. Monsoons are found all around the world, but all have two seasons, wet and dry. Monsoons have two distinctive characteristics – temperature and precipitation, with temperature being high, but variable, all year, and precipitation high during the wet season. Monsoons bring with them both benefits and problems to the local people, with some consequences of the monsoon having both a positive and negative effect i.e. flooding. Overall, people of the tropical monsoon region are reliant on these rains, and any change in their pattern causes devastating effects on the people, environment and economy.
Outline Plan
Introduction – What is a monsoon?
Where is the tropical monsoon climate found?
How monsoons vary?
Brief of characteristics common to all monsoons.
Main Body – Winter monsoon – formation,
Summer monsoon - formation
Distinguishing characteristics to monsoons - temperature
- precipitation
The effects of the monsoon on agriculture, people, and the economy –
-benefits
- problems
Conclusion – summary of main points