NCERT Class 9 Solutions: Climate (Contemporary India-I) Chapter 4– Part 7
Q5. Describe the regional variations in the climatic conditions of India with the help of suitable examples.
Major Climates in India
Tropical wet (humid) Climate
These regions experience high temperatures (above 18 °C) which all year round even in the coolest month.
Tropical wet (dry, humid)
The west coastal lowlands, the Western Ghats, and southern parts of Assam have this climate characterized by high temperatures. These regions receive rainfall through monsoon.
Tropical wet and dry or savannah climate
Most of the Deccan Plateau has this climate. These regions have long and dry winters and early summers with temperature above 18 °C. Temperatures can get as high as 45 °C during May. The annual rainfall from monsoon is between 75 and 150 cm. There is one exception- Eastern Tamil Nadu gets its rainfall in late November to January through retreating monsoon.
Dry climate group
In these regions like the Thar Desert of Rajasthan, the rate of evaporation of water is more than the amount of precipitation. These can be further classified into:
Tropical semi-arid (steppe) climate
The strip of land between east of the Western Ghats and the Cardamom Hills experiences this climate. Due the rain shadow of the Western Ghats this region receives minimum and unreliable rainfall (40 and 75 cm annually). Region includes Karnataka, interior and western Tamil Nadu, western Andhra Pradesh and central Maharashtra. This area is not suitable for agriculture. However due to proximity of Arabian Sea, the temperature is moderate, with winters experiencing temperature between 20 °C and 24 °C. Summers are hot and try with average temperature of around 32 °C Rainfall in this region can be due to both supper and winter. Summer rainfall is received towards the north of Krishna River because of monsoon. South of the river rainfall also occurs in the months of October and November due to retreating monsoon, however the rains are already dried up by the time they reach this area.
Sub-tropical arid (desert) climate
Western Rajasthan with scanty rainfall falls in this region. The annual precipitation is less than 20 cm and is very erratic and unpredictable, with a few regions not getting any rainfall each year. Aravalli Ranges are too low to create a barrier for the incoming monsoon winds and hence they pass without giving much rainfall to this region. Rainfall is received mostly through cloud bursts which happen during months of July, August and September. The summer are hot (average temperature 35 °C, and maximum temperature frequently crossing 50 °C). Winters are harsh with temperatures below freezing in some areas. Even the diurnal range of temperature is large- about 14 °C during summer) and even higher in winter. People of this region many hardships and thus this a very sparsely populated region of India.
Sub-tropical semi-arid (steppe) climate
Just to the east and slightly north of the dry arid region is the temperate of subtropical dry region. It runs from Punjab and Haryana to Kathiawar including Delhi. This climate lies between the tropical desert to south and humid sub-tropical in the north-east. All the characteristics of this climate are less extreme than the desert climate. The rainfall is received primarily during monsoon. It is higher than the arid climate (30 and 65 cm) however it is still very unreliable. Temperatures are less harsh then desert climate- with maximum during summer going up to 45 °C. Minimum temperatures during winter frequently drop down to freezing. Humidity is not high during the monsoon. The natural vegetation mostly comprises of short coarse grass, however some coarse crops like jowar and bajra are also cultivated.
Sub-tropical humid climate group
The key characteristic of this region is that the temperature during the coldest months falls between 18 and 0 °C. That is it does not go below zero. Additionally there is high humidity.
Sub-tropical humid (wet) with dry winters
This climate is even less harsh compared to the sub-topical or tropical arid climate. It is experienced in the foothills of the Himalayas especially Punjab-Haryana plain, in Rajasthan towards the east of the Aravalli range and in Uttar Pradesh, Bihar, northern part of West Bengal and Assam. The rainfall received mostly through monsoon. It increases as we go from west to east from about 65 cm to 250 cm annually. This difference causes a wide variety of natural vegetation. In Northeastern regions near the Himalayas rainfall is very high. Mawsynram village situated this region (in East Khasi Hills district of Meghalaya) is the wettest place on Earth, getting an average rainfall of 1187 cm per annum. Dry winter winds blow down from the lowlands of north India towards the Bay of Bengal during this time. Early winter (October- November) these winds pick up moisture from Bay of Bengal and cause (retreating monsoon) rainfall along part of Tamil Nadu coast. The summers are hot with temperatures reaching 48 °C in the lowlands with May and June being hottest. Highlands are cooler. Areas like Delhi get fog and frost for a few weeks in winter due to Western Disturbances.
Mountain climate or highland climate or alpine climate
The mountains of Himalayan face a drop of 0.6 °C in temperature for every 100 m altitude. Therefore the climate type of along this mountain range, changes rapidly from nearly tropical along the foothills to tundra above the snow line. A heights, the surface contact with atmospheric air is reduced and the air is rarified. Therefore it, cannot hold or transmit much heat causing a big difference between temperatures in sun and shades, high diurnal range of temperature, and inversion of temperature.
There is a great variability of rainfall based on altitude. Northern side of the western Himalayas (trans-Himalayan belt) is arid, cold and generally wind swept with sparse and short vegetation. Most precipitation in this region falls as snow during late winter. The interior of Asia especially the Tibetan Plateau get very cold in winter. Himalayas protect the south area and rest of the India from these cold, dry, winds. The leeward side of the southern mountains receive less rain while the windward slopes get heavy rainfall from monsoon. Because of the prevailing dew point, the places lying between height of 1070 and 2290 m receive the heavy rainfall which decreases rapidly above 2290m. In winter (December to February) placed at altitudes above 1500m receive heavy snowfall.
The states of Jammu and Kashmir, Himachal Pradesh, Uttarakhand, Arunachal Pradesh and Sikkim experience this kind of weather.
Temperature and Rainfall Extremes
There are great regional variations in the climatic conditions of India, in terms of temperature, precipitation and physical features.
There is great variation in diurnal temperature in the desert regions of Rajasthan. Additionally, the maximum annual temperature can get as high as 50°C.
On the other hand in on the peaks of Himalayas the temperature can go as low as -20°C. The snow there doesn’t melt even in summer.
Temperatures in Kerala and in Andaman and Nicobar islands remain uniform throughout the year.
The peaks of Himalayas get the precipitation in the form of snow while in the rest of the country rainfall is the main source of precipitation.
Precipitation is very heavy in Meghalaya with two of the wettest places on earth (Mawsynram and Cherrapunji) found in the region. Mawsynram village is situated in East Khasi Hills district of Meghalaya. It is the wettest place on Earth, getting an average rainfall of 1187 cm per annum.
On the other hand annual precipitation is less than 10 cm in parts of Rajasthan and Ladakh.
Tamil Nadu, receives rainfall during winter due to South-west monsoon (October to December) while rest of the country receives rainfall during summer (June to September).
Northwest India including Punjab, Haryana, Uttar Pradesh and Delhi receive rainfall in winder due to Western Disturbances.
Different regions of India have different physical characteristics affecting the climate. The coastal regions like Tamil Nadu and Maharashtra have fair weather all year along. The hilly regions of Western Ghats, Eastern Ghats and Himalayas have temperate to tundra kind of vegetation depending on the height
Q6. Discuss the mechanism of monsoons.
Wind Directions: Monsoon and Easterlies
The prevailing wind direction in India is north east due to north-easterly winds which blow from sub-tropical high pressure belt of northern hemisphere. The monsoon, causes the seasonal reversal in wind direction so that the windows now flow from the seas and oceans in the south towards the land mass in north. Such a reversal due to monsoons causes most of the rainfall received in India.
The Intertropical Convergence Zone or ITCZ
The key for understanding the monsoon and wind reversal is to look closely at the difference between annual temperature trends over land and sea. The position of maximum solar insolence oscillates from the Tropic of Cancer to the Tropic of Capricorn.
The northeast and southeast trade winds (easterlies) converge in this low pressure zone, which is also known as the Intertropical Convergence Zone or ITCZ. However the exact latitude of maximum low pressure region created by solar insolence changes its position depending on time of year. When the ITCZ shifts towards East Asia, sub-Saharan Africa, Australia and the southern parts of North America, there is rainfall in these regions.
During Indian summers, the Thar Desert and adjoining areas of the northern and central parts of the Indian subcontinent heat up. Due to high solar insolence and the heating of Earth’s surface the air along the surface gets warm and rises up creating a low pressure over Indian Subcontinent. This low pressure causes continuous movement of moist wind from seas and oceans in the south to the land masses. This wind moves from seas in the south to the landmass in the north thus reversing the direction
Progress of Monsoon
The southwest monsoon (or simply monsoon) has two branches:
Bay of Bengal Branch
The Bay of Bengal branch, starts with the Coromandal Coast northeast from Cape Comorin to Orissa, and then moves northwest towards the Indo-Gangetic Plain. This is the branch which causes heavy rainfall in the northeastern India.
Arabian Sea Branch
This branch of monsoon winds moves towards a low-pressure area over the Thar Desert. This branch moves northeast towards the Himalayas. Though it is roughly three times stronger than the Bay of Bengal branch, most of the moisture in this branch is exhausted when it hits the Western Ghats.
Timing of Monsoon
If monsoon starts on time, it follows roughly following schedule. However the start of monsoon is highly unpredictable.
25th May: The monsoon breaks over Indian Territory over Andaman and Nicobar Islands
1st June: It strikes the Indian mainland near the Malabar Coast of Kerala.
9th June: It reaches Mumbai.
29th June: It reaches Delhi.
5th July: Entire country experiences monsoon rain. However, on average South India receives more rainfall than North India except Northeast which receives most precipitation.
August End: Monsoon clouds begin retreating from North India.
September: With cooling of Indian landmass, the monsoon slowly starts weakening and withdrawing.
5th October: By now monsoon has withdrawn from Mumbai.
November: By the end of November, Monsoon has left the country.
Official Declaration of Monsoon
As the Indian highlands cool the seas of Bay of Bengal is warm. Due to this the winds start flowing from the Indian mainland towards the ocean. These north-east winds on their way pick up moisture from Bay of Bengal and cause heavy winter rainfall on the coast of Tamil Nadu in September and October.
India Meteorological Department (IMD), the official weather agency, declares onset of monsoon in Kerala when the following criteria are satisfied for 2 consecutive days after 10th May (defined in 2005):
At least 8 of 14 meteorological stations in Kerala ought to report rainfall of 2.5 mm or more.
Minimum range of wind speed
Presence of characteristic heat waves called Outgoing Longwave Radiation
Steady pattern of the monsoon winds at specified height in the atmosphere.
Q7. Give an account of weather conditions and characteristics of the cold season.
In the northern plains the temperature ranges between 10°-15°C.
Most places during this time have low temperatures and low humidity, clear skies and feeble winds.
Exceptions are the Western Disturbances which cause fog and rainfall in From the west inflow of the cyclonic disturbance and the northwest is a specific feature of the cold weather over the northern plains. Western Disturbances are the principle source of rain during non-monsoonal months especially over Northwest India including Punjab, Haryana, Uttar Pradesh and Delhi. Their effect sometime extends up to Gangetic plains and Northeast India. They are also responsible for bringing snowfall in the higher reaches of Jammu & Kashmir, Himachal Pradesh and Uttarakhand.
Q8. Give the characteristics and effects of the monsoon rainfall in India.
The monsoon is famous for its uncertainties. In one year the monsoon can be good and in the very next poor. Unfortunately agriculture in India depends on monsoon. Failure of monsoon any year spells doom for Indian agriculture and for millions who directly and indirectly depend on agriculture. This makes ensuring food-security very challenging for country like India.
Even in a “good monsoon” season, there can be long “breaks” in rainfalls. That is there can be several dry days before rains pick up again.
Additionally, the rainfall during monsoon can be very heavy. There are periods of heavy rainfall and cloudbursts which cause flooding.
Across the country monsoon has a large range in available precipitation. Precipitation is very heavy in Meghalaya with two of the wettest places on earth (Mawsynram and Cherrapunji) found in the region. Mawsynram village is situated in East Khasi Hills district of Meghalaya. It is the wettest place on Earth, getting an average rainfall of 1187 cm per annum. On the other hand annual precipitation is less than 10 cm in parts of Rajasthan and Ladakh.
To escape summer heat, Indians are eagerly waiting for start of monsoon. However the exact time of onset of monsoon is uncertain. Most years it is late or early by a few weeks, however even a few days of delay can cause great damage to rainfall dependent Indian agriculture.