Indian Physical Geography Notes: Relief, Rivers & Maps

The longest mainland coastline is of Gujrat i.e. 2340.60 km and the longest overall coastline of Andaman and Nicobar island 3083.50 km

Shortest coastline is of Goa 193 km

Indian coastline is mainly in two parts.

1. Western Coastal Plain
2. Eastern Coastal Plain

Western Coastal Plain

• It extends from Run of Kutch of Gujarat to Kanyakumari/ Cape Comorin.
• It lies between western ghats and Arabian sea.
• It is an example of submergent coast.
• It is divided into many parts.

1. Gujrat Coast Gujrat Coastal Plain is mainly divided into two parts
   1. Kutch coastal Plain
      • It is the western most part of Gujrat.
      • It is full of marshy areas, saline lakes, creeks
   2. Kathiawar Plain
      • It extends all across the Gulf of Khambhat, on either side.
      • It is full of estuaries of rivers like the Sabarmati, Mahi, Narmada, and Tapi.
2. Konkan Coast
   • The Konkan Coast extends from Daman in the north to Goa in the south.
   • It is a rocky coast.
   • It is characterized by numerous creeks and small river valleys, such as those of the Ulhas, Savitri, and Vashishti rivers.
   • Major cities on this coast include Mumbai and Goa.
3. Kanara (Kannada) Coast
   • The Kanara (Kannada) Coast extends from Goa to Mangaluru.
   • It is famous for its numerous waterfalls.
   • South of Goa, the Western Coastal Plain becomes very narrow.
4. Malabar Coast
   • The Malabar Coast extends from Mangaluru to Kanyakumari.
   • It is famous for its lagoons and backwaters.
   • Backwaters are narrow channels of seawater that extend inland.
   • In Kerala, backwaters are locally called Kayals.
   • These are famous for houseboats and Vallamkali.
   • It is famous of Vemebnat lake and Ashtamudi lake.

Eastern Coastal Plain

Eastern coastal plain stretches from West Bengal in the north to Kanyakumari in south. It is an example of emergent coast. It is often wider than western coast. It lies between eastern ghats and Bay of Bengal.

It is divide into three regional parts.

1. Coromandel Coast
   • It lies primarily in Tamil Nadu
   • It is famous for its Kaveri delta.
   • Major cities are Chennai, Tutikorine.
2. Northern Sarkar
   • It mainly covers Andhra Pradesh thus called Andhra coast also.
   • It has famous Godavari delta, Krishna delta and Kolleru lake.
3. Uttakal Coast.
   • It is mainly in Odisha.
   • It is famous for Mahanada Bhramini delta and Chilka Lake.
   • It is famous for olive ridley turtles, which are endangered species.

Island

• 

Andaman and Nicobar Island

Andaman and Nicobar islands are UTs and it is the one of the most important island territory due to its location near Strait of Malacca i.e. one of the busiest maritime trade route.

• It is union territory since 1956.
• It has island, islets and rocky outcrops more than 800
• Inhabitant island 31
• It has three district
  1. Northern and Middle Andaman
  2. Southern Andaman
  3. Nicobar
• Its highest peak is Saddle peak and the altitude is 732 m.
• Its southern most point is Indira point in Great Nicobar.
• It is separated from Myanmar by Coco channel and from Indonesia, Sumatra island by 6 degree channel.

Formation of Andaman and Nicobar Island

• The island are part of Arakanyoma mountain system which continues under water from Myanmar to Indonesia.
• It was formed due to convergence between Indo-Australian plate and Burma plate.
• Indian plate is subducting beneath Burman plate.

Division of Islands

1. Andaman Group
   1. Northern Andaman / Narcondam Island Extinct Volcano
   2. Middle Andaman Barren Island Only active volcano of India 130+ km east from middle Andaman Eruption started in 1990s
   3. Southern Andaman Port Blair
   4. Duncan Passage It is a water channel. It separates southern Andaman from Little Andaman
2. Nicobar Group
   1. Car Nicobar It is separated from Little Andaman by 10° Channel
   2. Little Nicobar, Nancowry Island
   3. Great Nicobar Great Nicobar is separated from rest of Nicobar group by Pryce Channel and Sombraro Channel Great Nicobar has southern most point of India i.e. Indira point.
   4. 6° Channel It separates Andaman Nicobar and Indonesia.

New Name Changes

Besides this on 23^rd January 2023 government of India name 21 previously unnamed island after 21 Param Vir Chakra recipients.

Important Tribes of Andaman

1. Andaman Tribes
   1. Great Andamanese
   2. Jarawa
   3. Onge
   4. Sentinelese
2. Nicobar Tribes
   1. Nicobarese
   2. Shompen

Lakshadweep

Lakshadweep has a literal meaning of a region where thousands of island are. British called it Laccadivi islands. It is group of more than 36 coral islands in Arabian sea. It is smallest UT of India. It is governed by central government. It has three major group of island

1. Amindivi island
   • It is northern most group.
   • Important island are Amini, Kadmad, Kiltan, Cheltan and Bitra.
2. Cannanore island
   • It is called Laccadivi island also.
   • It is central group of island.
   • Its important island are Androdd, Kavaratti(capital), Kalpani, Agatti and Bangran.
3. Minicoy island
   • Minicoy is the largest island.
   • It is separated from Cannanore island group by 9° Channel and from Maldives by 8° Channel.

• The official language of Lakshadweep
• It is famous for its high biodiversity, coral formation, eco tourism.
• It is inhabited by schedules tribes mostly there follower of Islam (unlike Andaman and Nicobar PVTs are there)

Drainage System of India and Drainage Pattern

Himalayan drainage system is mainly categorized into two

1. Antecedent River System
2. Consequent River System

Antecedent River System

An antecedent river system is a river that existed before the formation or uplift of the present day mountains or landforms. As the land gradually rises due to tectonic forces the river maintains its original course by cutting down into the rising terrain through vertical erosion.

Formation

• River established its course on a relatively flat surface.
• Tectonic uplift, mountain building occurs slowly.
• The river erodes downward at a rate equal to or greater than the uplift.
• Deep gorges are formed.

Characteristics

• These river are older than mountain range.
• Cuts across mountain ranges instead of flowing around them.
• Form deep valleys, gorges and canyons
• e.g. are Satluj river cuts through Himalayas and enter into India through Shipkila pass, Himachal Pradesh, Brahmaputra river cuts through Himalaya and enter into India through Arunachal Pradesh and forms Yarlung Tasngpo or Brahmaputra gorge, similarly Indus river, Kosi river, Gandhak river, Gagra river, etc.

Consequent River

Consequent river are those river which follow the regional slope gradient. If slope gradient changes it also changes its course e.g. Ganga, Yamuna, etc.

Himalayan rivers are categorized mainly into two

1. West flowing rivers of Himalaya - Indus River System
2. East flowing rivers of Himalaya - include Ganga and Brahmaputra rivers system

Peninsular Rivers

Peninsular rivers are of two types

1. East flowing - which drain into Bay of Bengal like Subarnarekha, Brahmani, Mahanadi , Godavari, Krishna, Kaveri, etc.
2. West flowing - which drain into Arabian seal like Luni, Sabarmati, Mahi, Narmada, Tapi, Mandovi, Juari, Peiyar, Pambiyar, Pamba, Bharathapuzha, etc.

Drainage Patterns

Diverse physiography which has given diverse drainage pattern. Drainage pattern means the direction of river flow, the way tributaries of main river join them e.g. at which angle, etc. Major drainage patterns are

1. Dendritic Pattern
   • It develops on uniform rock surface, resembles the branches of a tree.
   • Tributaries of the main river join it at acute angle along with a gentle slope.
   • e.g. Ganga, Godavari, Krishna, Indus, etc.
2. Trellis Pattern
   • In this river flow parallel to the hills and tributaries join the main river at right angle.
   • e.g. rivers of Vindhyan and Satpura range region.
3. Centrifugal Pattern
   • It is called radial pattern also.
   • In this river flow outward from a central highland.
   • e.g. Amarkantak plateau from where Son and Narmada originates and radiate out in different directions
4. Centripetal Pattern
   • where number of rivers flow into a common depression
   • e.g. Lake Loktak of Manipur, Lake Sambhar of Rajasthan.
5. Linear Pattern
   • When river flow parallel to each other.
   • e.g. rivers flowing out from the western slope of western Ghats.
   • It is called parallel drainage pattern also.

Factors Influencing Drainage pattern in India

1. Relief and Slope River flow from high to low areas/ slope gradient.
2. Geological Structure Hard and soft rocks influence direction and shape of the river because soft rocks are eroded more than the hard rock e.g. Trilece pattern
3. Climate and Rainfall Heavy rainfall creates dense drainage network e.g. Assam, Manipur whereas dry region may have sessional and inland drainage e.g. western Rajasthan.
4. Topography It includes mountains, plateaus, depression, etc. e.g. radial or centrifugal drainage system in plateau area and dendritic drainage system in plain areas.

Himalayan River System

Indus River System

• Indus river system is one of the three major Himalayan river system of India.
• Indus river originates from near lake Mansarover close to the Kailash range in Tibet, China
• It enters India near Themchok of Ladakh.
• It flows through Ladakh then into Pakistan and finally empties into Arabian sea east to Karachi.
• It flows through Indian states and UTs of Ladakh, J&K, Punjab, Himachal Pradesh (Indus river system).

  

• Its tributaries are
  1. Left Hand Tributaries
     1. Jhelum Originates of Verinag spring of J&K flows through Wular lake and Srinagar
     2. Chenab It is formed due to confluence of Chandra and Bhaga rivers at Tandi, Himachal Pradesh. It is largest tributary by volume of water
     3. Ravi Originates from Rohtak pass of Himachal and forms border between India and Pakistan.
     4. Beas Originates from Vyus Kund near Rohtak pass. It flows entirely in India
     5. Satluj Originates from Lake Rakas, Tibet, China. It is longest tributary of Indus.
  2. Right Hand Tributaries
     1. Shyok
     2. Gilgit
     3. Nubra
     4. Hunza
     5. Sihgar
     6. Zanskar
• Major dams and hydropower projects

Indus water treaty was signed between India and Pakistan in 1960 at Karachi. This was mediated by World Bank. As per this treaty India share 80% water of west of the west flowing rivers of Indus and tributaries which include Indus, Jhelum and Chenab and make use of east flowing tributaries of Indus for its own that includes Ravi, Beas and Satluj.

However following April, 2025 Pahalgam terrorist attack India announce that it had placed Indus water treaty in abeyance. Before terrorist attack, after Uri attack also India had made this strong decision and conveyed this to Pakistan that it won't be respecting this agreement unilaterally

Brahmaputra River System

• Brahmaputra river originates from Choma Yung Dung or Angasi glacier of Tiber near Mt. Kailash.
• It flows eastward and called Yarlung Tsangpo.
• It takes dramatic U trun and enter into Arunachal Pradesh from near Namchabarva peak.
• In Arunachal Pradesh it is called Dihang or Siang.
• In Assam, near Sadiya where Lohit river joins Dihang it gets its name Brahmaputra and it called Brahmaputra uptill Dhubri/ Assam.
• Thereafter it enter into Bangladesh as Jamuna. Their it is joint by Padma (Ganga) and together these are called Megna which forms Ganga Brahmaputra delta.
• It flows through state of Arunachal and Assam.

  

• Major tributaries are
  • Left hand tributaries
    • Dibang, Arunachal
    • Lohit, Arunachal
    • Dhansiri, Nagaland Assam
    • Kopili, Meghalaya Assam
  • Right hand tributaries
    • Subansiri, Arunachal
    • Kamang (Gia Bharali), Arunachal and Assam
    • Manas, Bhutan and Assam
    • Sankosh, Bhutan and Assam
    • Beki, Bhutan and Assam
    • Raidak, Bhutan West Bengal and Assam
    • Tyista, Sikkiam and West Bengal and join Brahmaputra in Bangladesh

Ganga River System

• Ganga river system is most important river system of North-Indian plain and one among three Himalayan river system.
• Ganga river originates as Bhagirathi River from Gangotri Glacier, from Gaumukh, Uttarakhand at the attitude of 3892 m.
• At Devprayag Alaknanda joins Bhagirathi and from this point the river is officially called The Ganga.
• Alaknanda river originates from Satopanth and Bhagirathi Kharak glacier near Chaukamba peak Uttarakhand.
• Alaknanda carries more water than Bhagirathi before meeting at Devprayag.
• Major tributaries of Alaknanda are
  1. Dholi Ganga
  2. Nandakini
  3. Bindar
  4. Mandakini

• 

Panchprayag (five scared confluences)

1. Vishnuprayag: Alaknanda + Dholi Ganga
2. Nandprayag: Alaknanda + Nandakini
3. Karnprayag: Alaknanda + Bindar
4. Rudhraprayag: Alaknanda + Mandakini
5. Devprayag: Alaknanda + Bhagirathi

It is right sequence of Panchprayag north to south.

• Ganga river thereafter i.e. after Devprayag flows through Rishikesh and Haridwar.
• At Haridwar it enters into plain.
• Thereafter its direction become west to east.
• Thereafter it reaches Kannauj > Kanpur > Prayagraj > Varanasi > Ghazipur > Buxar and Chhapra > Patna > Begusarai > Khagaria > Bhagalpur > Katihar > Kursela > Farakka Barrage > Bangladesh

Near Farakkha Barrage near West Bengal Ganga is bifurcated and formed a distributary called Hugli. Hugli rivers flows through West Bengal north to south. Kolkata city is situated on it.

After Farakka Barrage the main river flows through West Bengal as Bhagirathi river

After entering into Bangladesh it is called Padma river where it is joined by Jamuna and together these are called Meghna which formed Sundarbans delta i.e. largest delta in the world.

Tributaries of Ganga

• Left Bank Tributaries
  1. Ram Ganga
     • Ram Ganga originates from Ghadwal Himalaya, Uttarakhand.
     • It flows through Uttarakhand and Uttar Pradesh.
     • It joins Ganga at Kanoj.
     • Important Dams is Kalagarh Dam also called Ram Ganga dam.
  2. Gomati River
     • Gomati River originates from Gomat Taal, Pilibhit district of Uttar Pradesh
     • Major cities situated on it are Lucknow, Sultanpur and Jaunpur.
     • It joins Ganga east to Varanasi at Ghazipur.
     • Major barrage is Gomati barrage.
  3. Ghaghra River
     • It is called Karnali river in Nepal.
     • It originates form Mapchachungo glacier, Tibet.
     • It joins Ganga near Chaapra and forms Northern border between Uttar Pradesh and Bihar.
     • It important tributary is Sarda and Sarju on which Ayodhya is situated.
     • Its other important tributary is Rapti on which Gorakhpur is situated which is famous for Gorakhnath Temple. Gorakhnath was founder of Nath sept.
     • The major dams on Ghaghra are
       1. Girijapuri Barrage in India.
       2. Karnali Hydropower project in Nepal.
  4. Gandak River
     • It is called Narayani river also.
     • It originates from Nepal Himalaya between Dhaulagiri and Annapurna.
     • This river joins Ganga near Patna, Bihar.
     • Major dam is Valmiki Barrage.
  5. Budhi Gandak River
     • Budhi Gandak originates from Someshwar Hills, west Champaran, Bihar
     • It flows completely in Bihar and joins Ganga near Khagaria, Bihar.
  6. Kosi River
     • Kosi river originates from Tibet as Arunkosi, Sonkosi, Tamurkosi.
     • It joins Ganga at Kursela, Katihar of Bihar.
     • It is called Sorrow of Bihar.
     • Famous dam is Kosi Barrage at Bhimnagar.
  7. Mahananda River
     • Mahananda river originates from Darjeeling hills West Bengal from their it enter into Bihar, again goes back into West Bengal and finally joins Ganga in Bangladesh.

In 2025-26 under National Mission for Clean Ganga, a master plan has been aproved to restore Gomati rivers origin site at Pilibhit focusing on ecological restoration and cultural heritage.

The first bassin wide Gharial survey released in 2026 has covered 13 rivers of Ganga bassin. After the Chambal important Gharial populations were also recorded in Ghagra Girwa river system.

• Right Hand Tributaries of Ganga
  1. Yamuna River
     • Yamuna River Originates from Yamunotri glacier, Bandarpoonch peak Uttarkashi, Uttarakhand.
     • Elevation is 6315m.
     • It flows through Uttarakhand, Himachal Pradesh, Haryana, Delhi, Uttar Pradesh (5 states).
     • It joins Ganga at Prayagraj.
     • It is largest tributary of Ganga.
     • Major tributaries of Yamuna are
       • Left Hand tributaries
         1. Tons
            • It is largest tributary of Yamuna from left hand side.
         2. Hindon
            • Hindon originates from Saharanpur, UP and joins Yamuna near Noida.
       • Right Hand Tributaries
         1. Chambal
            • Originates from Janapav hills, Vindhyan range, Madhya Pradesh.
            • It joins Yamuna near Itawah.
            • Its major tributaries are
              • Banas
              • Kali Sindh
              • Parvati
              • Shipra
            • Major dams of Chambal are (south to north)
              • Gandhi Sagar
              • Rana Pratap Sagar
              • Jawahar Sagar
              • Kota Barrage
            • Chambal is famous for
              • Ravines -Gharial, Magar and Crocodile
              • Gangetic Dolphin habitat.
            • It flows through three states UP, MP and Rajasthan.
         2. Sindh
            • Sindh river originates from Vidisha district of Madhya Pradesh.
            • It joins Yamuna near Itawah district, Uttar Pradesh.
            • The famous dam on it is Manikheda Dam
         3. Betwa
            • Betwa river originates from Vindhyan hills near Bhopal.
            • Important dams on Betwa river are
              1. Mata Tilla Dam
              2. Raj Ghat Dam
              3. Parichha Dam
         4. Ken
            • Ken river originates from Katni district of Madhya Pradesh and joins Yamuna near Chilla, Uttar Pradesh.
            • Major dam is Gangau Dam.
            • It passes through Panna Tiger reserve of Madhya Pradesh.
  2. Karmnasa River
     • Karmnasa river originates from Kamur hills.
     • Vindhyan range in eastern UP and Bihar known as Kamur hills.
     • It joins Ganga near Buxar at Chausa.
     • It forms border between UP and Bihar.
     • Important dams on this river are
       • Latif Shah Dam
       • Durgavati Reservoir
  3. Son River
     • Son river originates from Amarkantak plateau, MP.
     • It flows through MP, UP, Jharkhand and Bihar.
     • It joins Ganga west to Patna.
     • Its tributaries are
       • North Koyel
       • Rihand
       • Johila
     • Major dams are
       • Indrapuri Barrage, Bihar
       • Rihand Dam
       • Bansagar Dam
     • It second largest right bank tributary of Ganga after Yamuna.
  4. Punpun River
     • It originates from Chota Nagpur Plateau, Jharkhand.
     • It joins Ganga east to Patna city.
     • Falugi is tributary of Punpun on which Bodh Gaya is situated.

Ken Betwa river linking project remains India's first river linking project under implementation.

In 2026 researchers from IISER, Bhopal and University of Delhi has reported that Yamuna in Delhi has shrunk by 68% over the last 200 years, highlighting the impact of urbanization, encouragement and barrage construction.

Tributary of Hooghly

1. Damodar River
   • Damodar river originates form Chota Nagpur plateau of Jharkhand.
   • It flows through Jharkhand and West Bengal.
   • It joins Hooghly, a distributary of Ganga near Falta of West Bengal.
   • Its major tributaries are
     • Barakar
     • Konar
     • Bokaro
     • Jamunia
   • Major dams of Damodar
     • Tilaya Dam on Barakar river
     • Maiton river on Barakar river
     • Konar Dam on Konar river
     • Panchet Dam
     • Tenu Ghat Dam
     • Durgapur Barrage
   • Damodar river was called sorrow of Bengal.

Peninsular Rivers

These are categorized into two parts

1. East flowing river of Peninsular India.
2. West flowing river of Peninsular India.

East Flowing Rivers

1. Swarnrekha River
   • This river originates from Chhota Nagpur plateau and drains into Bay of Bengal.
   • It forms estuary.
   • It forms northern boundary of Utakal coastal plain.
2. Brahmani River
   • Brahmani is formed by the confluence of south Koel and Sankh river.
   • These two rivers joins each other at Vedavyas near Rourkela in Odisha.
   • It flows through Jharkhand and Odisha.
   • It joins Baitarani river near Dharma and forms its delta in Bay of Bengal.
   • Rengali dam is built of Brahmani river.
   • Bhitarkanika National Park, which is famous for olive ridley turtles, salt water crocodiles is near its delta.
3. Mahanadi River
   • Mahanadi river originates from Sihawa in Dhamtari district of Chattisgarh.
   • Thereafter it flows northward and enter in Odisha. Its small part flows into Jharkhand also.
   • It forms its delta in Bay of Bengal.
   • Its delta formation starts from Cuttack of Odisha.
   • Near its delta Puri, a famous temple city is situated.
   • South to its delta famous Chilika lake is there which is famous Ramsar site.
   • Its tributaries are
     • Left bank tributaries
       1. Seonath (longest tributary)
       2. Hasdeo
       3. Mand
       4. Ib
     • Right bank tributaries
       1. Tel (largest right bank tributary)
       2. Ong
       3. Jonk
   • The famous dams on it are
     1. Hirakund Dam near Sambalpur district of Odisha.
     2. Gangrel Dam (Ravishankar Sagar) in Dhamtari district of Chhattisgarh
     3.  Minimata Bango Dam built on Hasdeo river.
   • The major cities on Mahanadi are
     1. Raipur
     2. Sambalpur
     3. Cuttack
   • There are two tiger reserves on this
     1. Satkosia Tiger Reserve
     2. Udanti Sitanadi Tiger Reserve
   • The famous waterfall is Deodhara fall
   • There is a river water sharing dispute between Chhattisgarh and Odisha.
4. Godavari River
   • Godavari river originates from Kalsubai hills in Trimbakeshwar, Nasik.
   • It is largest river of peninsular India.
   • It is also called Dakshin Ganga along with Kaveri.
   • It is second longest river in India after Ganga.
   • It flows through Maharashtra, Telangana, Andhra Pradesh.
   • It forms delta in Andhra Pradesh near Antarvedi
   • It tributaries are
     • Left bank tributaries
       1. Pranahita
       2. Indravati
       3. Sabari
       4. Purna
     • Right bank tributaries
       1. Manjra
       2. Mula
       3. Kinnerasani
       4. Maner
   • Major dams are
     1. Jayakwadi Dam (one of the largest irrigation project in Maharashtra)
     2. Sriram Sagar Dam
     3. Polavaram Multipurpose Project
     4. Nizam Sagar Dam (built on Manjra river)
   • Major cities are
     1. Nasik
     2. Nanded
     3. Nizamabad
     4. Rajahmundry or Rajamahendravaram
     5. Bhadrachalam.
   • Major national parks and tiger reserves on Godavari Basin are
     1. Papikonda National Park
     2. Indravati National Park
     3. Kawal Tiger Reserve
   • Important waterfall are
     1. Chitrakote Falls, often called Niagara Falls of India.
     2. Duduma Fall on Sabari river.
   • On Godavari river Khumb mela is celebrated at Nasik.
   • There is dispute between Telangana and Andhra Pradesh on river water sharing.
5. Krishna River
   • Krishna river originates from Mahabaleshwar of Sahyadri hills, from Satara district of Maharashtra.
   • It is second largest east flowing river of peninsular India after Godavari.
   • It flows through Maharashtra, Karnataka, Telangana and Andhra Pradesh.
   • It forms delta in Andhra.
   • Between delta of Godavari in north and delta of Krishna in south Kolleru Lake is situated.
   • Major tributaries are
     • Left bank tributaries
       1. Bhima is largest tributary, flows mainly through Maharashtra and Karnataka.
       2. Musi on which city of Hyderabad is situated.
     • Right bank tributaries
       1. Tungabhadra is longest right bank tributary.
       2. Ghataprabha
       3. Malaprabha
       4. Koyna is known for reservoir induced earthquake which occur due to Koyna dam.
   • Major dams are
     1. Nagarjuna Sagar Dam
     2. Srisailam Dam
     3. Almatti Dam
     4. Basava Sagar Dam (popularly known as the Narayanpur Dam)
     5. Koyna Dam
     6. Tungabhadra Dam
   • Important cities are
     1. Vijayawada
     2. Amravati
     3. Hyderabad
     4. Pune
     5. Karnol
   • Important national parks are
     • Nagarjunasagar-Srisailam Tiger Reserve
     • Koyna Wildlife Sanctuary
   • Important waterfalls are
     • Gokak Waterfalls
     • Ethipothala fall
   • Inter state dispute between Maharashtra, Karnataka, Telangana and Andhra Pradesh.
6. Pennar River
   • Pennar river originates from Nandi Hills of Karnataka.
   • It flows through Karnataka and Andhra Pradesh and forms its estuary and grand canyon called Gandikota in Andhra.
   • Important dams are
     1. Somasila Dam
     2. Mylavaram Dam
     3. Penna Ahobilam Dam / PABR Dam
   • Major city is Anantapur.
7. Kaveri River
   • Between Kaveri river delta and Pennar river there is Pulicat Lake which extends between Andhra Pradesh and Tamil Naidu. It is separated of Bay of Bengal by Sriharikota island.
   • Kaveri river is called Dakshin Ganga along with Godavari.
   • It originates from Talakaveri from Brahmagiri Hills of Western Ghats and flows through states of Karnataka and Tamil Naidu.
   • However, it basin extends into Kerala and Puducherry also.
   • Its major tributaries are
     • Left bank tributaries
       • Harangi
       • Hemavati
       • Shimsha
       • Arkavati
     • Right bank tributaries
       • Lakshmana Tirtha
       • Kabini (Kapila)
       • Bhavani
       • Amaravathi
   • Major cities on it banks
     • Madikeri
     • Mysuru
     • Srirangapatanam
     • Tiruchirappalli / Trichey
     • Thanjavur (famous for silk and green revolution)
   • Important waterfalls are
     • Shivanasamudra Falls on Kaveri river
     • Hogenakkal Falls on Kaveri river near Karnataka-Tamil Naidu border
     • Abbey Falls on tributary on Kaveri basin
   • National Parks are
     • Nagarhole National Park (Kabini Basin)
     • Bandipur National Park
     • Mudumalai National Park
   • Kaveri delta is also known as the rice bowl of Tamil Naidu. Chhattisgarh is known as rice bowl of India.
   • Kaveri water dispute is between Karnataka, Tamil Naidu and Puducherry
8. Vaigai River
   • It is popularly known River of Madurai because the famous city of Madurai which is called Temple city of India is situated on its banks.
   • It flows only through Tamil Naidu.

West Flowing Rivers

1. Major Rivers of Kerala Kerala has about 44 rivers of which 41 are west flowing into the Arabian sea and 3 are east flowing as tributary of Kaveri that includes Kabini, Bhavani and Pambar.
   1. Periyar River
      • It is longest river of Kerala i.e. 244 kms.
      • Major dams are
        • Idukki Dam
        • Periyar Dam (Mullaperiyar Dam)
        • Edamlayar Dam
      • Important waterfalls are
        • Cheeyappara Waterfalls
        • Valara Waterfalls
      • Famous tiger reserve is Periyar Tiger Reserve.
   2. Bharathapuzha River
      • It is also called Nilo river.
      • It originates from Anamalai Hills.
      • Its length is 209 km.
      • Major dam are
        • Mangalam Dam
        • Malampuzha Dam
   3. Pamba River
      • It is third largest river of Kerala.
      • It flows through Vembanad Lake. Bembanad Lake is backwater lake.
      • Backwaters are called kayals. Kayal are used for boat race called Vallam Kali.
      • Sabarimala temple is located on its bank.
   4. Chaliyar River
      • It is fourth largest river of Kerala.
   5. Chalakudy River
      • It is fifth largest river of Kerala and length is 145 km.
2. Major rivers of Karnataka
   1. Sharavati River
      • It originates from Shivamogga district of Karnataka.
      • The famous Jog Fall is on this river.
      • It is also known for Sharavati Hydroelectric Project.
   2. Netravati River
      • It is main drinking water source for Mangaluru.
3. Major rivers of Goa
   1. Mandovi River
      • It originates from Western Ghats, Karnataka.
      • In Karnataka it is called Mahadayi River.
      • In Goa it is called Mandovi
      • It divides Goa into almost two equal parts.
      • Famous Dodhsagar fall is on this river.
      • The city of Panji and the old Goa is situated on its bank.
   2. Zuari River
      • It flows within Goa only.
      • Salaulim Dam is on this river.
      • Mormugao is on this river.
4. Tapi River
   • Tapi river originates from Multai in Satpura Range, Betul district of Madhya Pradesh.
   • It flows through Madhya Pradesh, Maharashtra and Gujrat and drains into Gulf of Khambhat near Surat.
   • The famous city of Surat is situated close to its estuary.
   • It flows through rift valley between Ajanta in north and Satpura range in south.
   • It longest tributary is Purna.
   • Other tributaries are Panzara River and Bori River.
   • Right bank tributaries are Gomai River, Arunavati River and Aner River
   • Major dams are
     • Ukai Dam
     • Hathnur Dam
     • Girna Dam
   • Major cities are
     • Surat, Gujrat
     • Bhusawal, Maharashtra
     • Burhanpur, Madhya Pradesh
   • Yawl Wildlife Sanctuary is important national park.
5. Narmada River
   • Narmada is longest west flowing river in India.
   • It flows through rift valley between Vindhyan range in north and Satpura in south.
   • It originates from Narmada Khund at Amarkantak plateau.
   • It flows through Madhya Pradesh, Maharashtra and Gujrat.
   • Its tributaries are
     • Left bank tributaries
       • Banjar
       • Sher
       • Shakkar
       • Dudhi
       • Ganjal
     • Right bank tributaries
       • Hiran
   • Dams are
     • Sardar Sarovar
     • Indira Sagar
     • Omkareshwar
     • Maheshwar
     • Bargi Dam
     • Tawa Dam
   • Important waterfalls is Dhuandhar Waterfall, Jabalpur.
   • Important national park is Kanha National Park.
6. Mahi River
   • It originates from Vindhyan Range from Dhar district of Madhya Pradesh and drains into Gulf of Khambhat.
   • It flows through Madhya Pradesh, Gujrat and Rajasthan.
7. Sabarmati River
   • Sabarmati river originates from Aravalli, Udaipur district.
   • It flows through Rajasthan, Gujrat and empties into Gulf of Khambhat.
   • Important cities are Udaipur, Gandhinagar, Ahmedabad.
8. Luni River
   • It originates from Aravalli near Pushkar.
   • It flows through Rajasthan and drains into Rann of Kutch or sea only during monsoon.
   • Tributaries are
     • Left hand tributaries
       • Sukri
       • Jawai (largest)
       • Guhiya
       • Bandi
     • Right hand tribuatries
       • Jojri
   • Major dams are
     • Jawai Dam
     • Hemawas Dam
   • Major cities are
     • Ajmer
     • Pali
     • Jodhpur
     • Barmer
   • Desert National Park and Jawai Leopard Conservation Reservation is important national parks.

Soil in India

India had one of the greatest soil diversities in the world because all soil forming factors vary amorously across the country which includes

1. Parent Rock Material

   It is outcome of the geology of the region because of long geological history of India specially Indian peninsular all varieties of parent rock including igneous, metamorphic and sedimentary rock.

2. Relief or slope gradient

   India had been subjected to various tectonic activities and that is why there are variety of relief like mountains and plateaus with diverse slope angle.

3. Climate

   Tropic of Cancer passes almost from the middle of the country but still entire India has almost tropical type of climate which is hot humid or hot dry. It is because

   • Long peninsular shape of India due to which Indian peninsular is projected deep into the Indian ocean which keep temperate moderately high and humid.
   • Presence of Himalayas in north, high mountains cold winds from the north i.e. Siberia does not enter into India that's why temperature does not fall beyond a certain degree even during winter season.
   • Himalayas also helps in checking northward advancement of south-west monsoon as well as distribution of monsoon rain over north Indian plain which make larger part of India warm and moist.
   • Because of high altitude mountains and plateaus even within the tropics many places experience temperate climate e.g. Bengaluru, Ranchi, Shillong, many Himalayan regions, etc.
   • Thus as per Koepen classification India has variety of climatic regions which include Am, Aw, Cwg, BSh, Dfc, Et, etc.

4. Vegetation Cover

   As per data more than 23% area is under forest cover. Forest provide good amount of humus and also control soil erosion.

5. Time

   It is very dominant factor because to make only one centimetre thick soil it take more than thousand year.

Soil Types in India

Alluvial Soil

• Alluvial soil is the most widespread and agriculturally important soil. It is formed by the deposition of sediments brought by rivers. It is categorized into
  • Khadar
  • Bangar
  • Terai
  • Bhabhar
• It is found in North-Indian plain, peninsular river valleys and the costal plains of India.
• Physical characteristics are
  • Its texture is sandy to clay.
  • It is highly porous thus excellent moisture retention.
• Mineral composition are
  • It is rich in lime, phosphoric acid, silica, potash and iron.
  • It is deficient in nitrogen, humus, phosphorous, zinc, boron and sulfur.
• It is suitable for all crops.

Black Soil

• It is formed mainly from weathering of Deccan trap Basaltic lava.
• It if famous as cotton soil or regur soil.
• Its black colour is due to presence of titaniferous magnetite.
• Its particle size is very fine because it was formed out of weathering basaltic lava that's why water retention capacity is very high.
• It become sticky when wet and hard when dry. This process is called self blowing effect also.
• It is found in Maharashtra, Madhya Pradesh, Gujrat, Andhra Pradesh, Karnataka, Telangana, Chhattisgarh.
• Physical characteristics are
  • Its texture is clayed and fine grain.
  • It is rich montmorillonite clay minerals that's why it swell up and shrinks when it is wet and dry respectively.
• Mineral composition are
  • It is rich in lime, iron, magnesium, aluminium and potash.
  • It is deficient in nitrogen, phosphorous, organic matter (humus), sulfur, zinc and boron.
• It is used for cotton, sugarcane, soyabean, tobacco, sunflower, maze, wheat, jawar, bajara, tur, gram, etc. oilseeds, horticulture, etc.

Wherever intensive agriculture is done soil faces deficiency of zinc and boron

Red soil

• It derived its red colour from ferric oxide as well as high diffusion of red colour.
• In those areas where rainfall is relatively high its colour become yellow.
• It is found in Tamil Naidu, Andhra Pradesh, Karnataka, Telangana, Odisha, Chhattisgarh, Jharkhand, Madhya Pradesh, Southern Rajasthan, Northern West Bengal.
• Physical characteristics are
  • Its texture is sandy to clay.
  • Porosity is high that's why its water holding capacity is low.
• Mineral composition are
  • It is rich in iron, potash and silica.
  • It is deficient in nitrogen, phosphorus, humus, lime, magnesium, zinc.
• In this depending upon availability of water all types of crops are grown like rice, millet, maze, pluses, oilseeds, cotton, tobacco, sugarcane and horticulture,

Laterite Soil

• Laterite soil is a residual soil formed under high temperature and heavy rainfall through the process of laterization.
• It is end product of intense weathering in tropical humid conditions where rainfall is more than 200 cm, temperature is high.
• It is found in Western Ghats, Eastern Ghats, North-East India, parts of Chhattisgarh and Jharkhand.
• Mineral composition
  • It is rich in iron oxide and aluminium oxide.
  • It is deficient in nitrogen, potassium, phosphorus and silica.
  • It is mostly used for plantation crops like tea, coffee, rubber, coconut, cashew, species like pepper, cardamom, horticulture like pineapple, banana, etc.
  • On pH scale it is acidic
  • It has poor moisture retention capacity.

Sandy Soil

• Sandy soil is outcome of the mechanical weathering in rocks specially in hot deserts and cold deserts where rainfall is less than 50 cm per annum and rate of evaporation is high.
• It is found in Thar desert of Rajasthan, Kutch and Saurashtra region of Gujrat, western Haryana and south-west Punjab.
• Its colour are light brown to yellowish. It is brown where water is less and yellowish where water is more.
• It permeability is very high that is why water holding capacity is very low.
• Mineral composition.
  • Soluble salts, lime, phosphates
  • It is deficient in nitrogen, humus, zinc and iron.
• It is suitable for wheat, mustard, cotton, horticulture like bear, dateplam, kinnow.

Mountain Soil

• It develop in hilly and mountainous regions under the influence of altitude.
• These are generally sallow and acidic on pH scale.
• These are found in Himalayan region, Western Ghats and Eastern Ghats.
• Its colour is dark to dark brown.
• It is rich in humus but highly susceptible to erosion.
• It is rich in organic matter and nitrogen and deficient in phosphorous, potash and lime.
• It is mostly used for forests, plantation crops like Tea, coffee, rubber, horticulture like apple, peach, kiwi, cherry, walnut, spices like cardamom, black prepper and food crops like maze, barley, potato, etc.

Bog soil / Peaty and Marshy soil

• These are formed in water logged conditions where oxygen is deficient.
• The dead plant remains are decomposed only partially that's why organic matter accumulates.
• These are found in high rainfall areas where there is poor drainage, water logging.
• Distribution is lake areas, swampy areas, wet lands, etc.
• Their colour is dark brown to black and acidic on pH scale.
• These are rich in organic carbon, humus and nitrogen.
• These are deficient in potash, phosphorous and lime/calcium.
• These have high biological importance however rice, jute are grown in feasible areas.

Saline and Alkaline Soil

• These are problem soils characterized by accumulation of soluble salts or sodium in the root zone.
• In India it covers about 6 to 7 million hectors.
• Naturally such soil occurs in low rainfall areas but present human induced causes are major concern which includes excessive irrigation, water logging and poor drainage.
• It is found Punjab, Haryana, Western Uttar Pradesh, Tamil Naidu, Andhra, etc.
• In north India it also called Reh, Kallar, Usar, Tuher, etc.
• The top layer of the soil becomes hard and dry which does not allow infiltration of water easily.
• On pH scale these are sometime more than 8.5
• These are rich in sodium chloride, sodium sulphate, sodium carbonate and calcium and magnesium salts.
• These are deficient in nitrogen, organic matter, iron and zinc and phosphorous.
• After reclamation it is used for rice, barley, wheat, oilseeds, fodder (All salt tolerant crops.)
• Gypsum application is done to treat soil

Soil Profile

Soil profile is a vertical section of soil that shows it different layers called soil horizon, from the surface down to the bed rock. It includes:-

1. O Horizon It contains dead leaf, plant remain and humus. However, this organic layer is not necessarily found in every soil.
2. A Horizon It is top soil. It is rich in organic matters and minerals. Most plants roots and soil organisms found here.
3. E Horizon It is eluviation layer. It is light coloured layer where clay, iron and alluvial have be leased down.
4. B Horizon Layer of sub-soil. It is zone of illuviation. In this iron and other minerals which were washed down from upper layers are accumulated.
5. C Horizon It is parent material. It is partially weathered rocks and mineral fragments.
6. R Horizon It is parent rock or bed rock which is still hard and un-weathered.

A soil profile helps in understanding soil formation, fertility, drainage and suitability for the agriculture and construction.

Soil Erosion

Soil erosion is the detachment, transportation and removal of fertile rock soil by natural agents such as water, wind, sea waves, glaciers or by human activities.

It reduces soil fertility, agriculture productivity and ecological stability. India looses million of tons of top soil every year making soil erosion a major environmental challenge.

Causes of Soil Erosion

1. Natural Causes
   1. Water Erosion Water erosion is done by heavy rain, flash flood, river bank erosion or cloud burst.
   2. Wind erosion It is very effective in arid and semi arid regions e.g. Thar desert.
   3. Glacier erosion In high altitude or in high latitudes.
   4. Sea wave erosion In coastal areas e.g. Odisha and Kerala coast.
2. Human causes
   1. Deforestation
   2. Over grazing
   3. Shifting agriculture
   4. Mining and Quarrying
   5. Unscientific agriculture practices
   6. Over irrigation
   7. Urbanization and infrastructure development.

Types of Erosion

1. Water Erosion
   1. Splash erosion Raindrops dislodge soil particles. High terminal velocity causes high splash erosion.
   2. Sheet erosion Uniform removal of thin layer of top soil over large area.
   3. Rill erosion Small channels/rills are formed by running water.
   4. Gully erosion Rill enlarges into deep gullies and gradually in ravines e.g. Chambal ravine in Madhya Pradesh, Uttar Pradesh and Rajasthan.
2. Wind Erosion
   1. Suspension Fine dust carried over long distances.
   2. Saltation Medium size particles bounce along the ground.
   3. Surface creep Large particles rolls along the surface.

Impact of Soil erosion

• Loss of fertile top soil
• Decline in crop productivity
• Siltation of rivers and reservoirs.
• Floods and landslides.
• Desertification
• Loss of biodiversity
• Reduce groundwater recharge.
• Global warming (due to released of trapped carbon dioxide).

Measurements to reduce Soil Erosion

• Afforestation and social forestry.
• Contour farming/Ploughing
• Terrace farming
• Shelterbelts and windbreaks
• Watershed management
• Check dams and gully ploughing
• Control grazing
• Conservation agriculture and sustainable agriculture
• Dryland farming.

Initiatives taken by GoI to check soil erosion

1. Integrated Watershed Management Program
   • Soil and water conservation through check dams, contour bunding, farm bonds and gully ploughing.
   • Now it is integrated under watershed development component of Pradhan Mantri Krishi Sinchayee Yojana (PMKSY).
2. Pradhan Mantri Krishi Sinchayee Yojana (PMKSY)
   • Promote per drop more crop.
   • Encourage micro irrigation and reduces runoff soil erosion.
3. National Mission for Sustainable Agriculture
   • Promotes conservation agriculture, agro-forestry and climate resilient farming.
4. National Afforestation Program and Green Indian Mission
   • Afforestation and restoration of degraded forest to stabilize slopes and reduce erosion.
5. VB–G RAM G
   • Construction of check dams, contour trenches, fields bunds and water harvesting structures.
6. Deforestation
   • National Action Program under the UN convection to combat desertification (UNCCT).
   • India has committed to achieving Land Degradation Neutrality (LDN) by 2030.
7. Soil Health card Scheme
   • Promotes balance fertilizers use and improves soil quality.
8. National Mission for clean Ganga
   • River bank protection, afforestation and flood plain management to reduce river bank erosion.

Monsoon

Monsoon is periodic wind system which reverses its direction after certain time. In India its direction south-west to north-east for 90 days and from north-east to south-west for 90 days. The word "monsoon" is derived from Arabic "Mausin".

Classical theory of Origin of Monsoon

The classical theory of Indian monsoon also known as thermal theory was proposed by Edmund Hally in 1688. It explains monsoon as a seasonal reversal of winds caused by the differential heating and cooling of land and sea.

Basic Principles

• Land heats up and cools down faster than the ocean due to difference in specific heat.
• This creates seasonal pressure differences.
• Wind always blows from high pressure to low pressure area.

Mechanism of Summer Monsson (June to September)

1. Formation of low pressure over land
   • During summer the Indian landmass becomes intensely heated.
   • A low pressure area develops over north-western India and adjoining Pakistan.
2. High pressure over Indian Ocean
   • The Indian oceans remains comparatively cooler.
   • A high pressure area develop over Indian Ocean.
3. Moisture loden wind
   • Wind blows from ocean towards the land.
   • While crossing Indian Ocean they absorb large amount of moisture.
4. Heavy Rainfall
   • On reaching India these moisture loden wind rise due to Western Ghats and Himalayas orographic rain and conduction rain due to high surface heating. This result in widespread rainfall.

Mechanism of Winter Monsoon (October to February)

• During winter lands cools rapidly.
• A high pressure area form over northern India.
• The ocean remains relatively warmer and crating low pressure area.
• Wind reverses direction and blow from land to sea.
• These are dry winds thud do not cause rainfall by enlarge but wind blowing over Bay of Bengal cause rainfall over Tamil Naidu.

Limitations of this theory

• Doesn't explain role of ITCZ.
• Unable to explain monsoon burst, monsoon break, failure of monsoon.
• Ignore the influence of Tibet plateau.
• Ignore the variation in the distribution of rainfall, etc.

However, it helps understand basic mechanism of summer and winter monsoon that's why it forms the foundation for the later monsoon theories.

Dynamic theory of Monsoon

Dynamic theory of monsoon is also known as Modern theory of monsoon. It explained Indian monsoon as global atmospheric circulation of atmospheric rather than differential heating of land and sea as suggested by classical theory.

It highlights the role of ITCZ, Tibet Plateau, jet streams and ocean atmosphere interaction.

Basic Theory

• The Indian monsoon is part of global wind circulation system.
• Its onset, intensity and withdrawal are controlled by seasonal migration of pressure belts and upper air circulation.

Role of ITCZ

• During summers the ITCZ shifts northward to the Indo-Gangetic plains.
• It creates a low pressure belt over North-Indian plain.
• Moisture loden wind from southern Indian Ocean cross the equator and turn rightward due to Coriolis force and reach the Indian Subcontinent as south-west monsoon and stays over India between June to first week of September.

North-East Monsoon

With the onset of winter season or with apparent equatorward movement of sun from Tropic of Cancer and thereafter its movement towards Tropic of Capricorn ITCZ is also started shifting equatorward thus the direction of wind reverses and first week of September it starts moving/blowing from Indian Subcontinent to the ocean and the direction of wind is north-east to south-west that's why it is called North-East Monsoon.

Factors responsible for strengthening of Indian South-West Monsoon

1. Heating of Tibet Plateau
2. Strengthening of Mascarene High
3. Tropical Easterly Jet (TEJ)
4. Somali Jet
5. Positive Indian Ocean Dipole
6. Active phase of Madden Julian Oscillation (MJO) on Indian Ocean during South-West Monsoon
7. La-Nina phase of ENSO

Factors responsible for weakening of South-West Monsoon

1. Poor heating of Tiber Plateau
2. Delayed northward (north to Himalayas) shifting sub-tropical westerly Jetstream
3. Negative Indian Ocean Dipole
4. Passive phase of Madden Julian Oscillation over Indian South-West Monsoon
5. El-Nino phase of ENSO
6. EN-Nino phase of

Role of Tibet Plateau heating in Indian Monsoon

Tibet Plateau with an average elevation of 4500 to 5000m is often called the heat engine or elevated heat source of Asia. During summers its intense heating plays a crucial role in strengthening the South-West Monsoon by influencing both surface pressure and upper air circulation.

Mechanism

1. Intense Heating of the Plateau
   • During May to June Tibet Plateau receives intense solar radiation.
   • Being at high altitude it heats the surrounding atmosphere efficiently.
   • Warm air rises, creating a deep thermal low over the plateau.
2. Formation of upper air low pressure
   • Rising warm air causes low pressure over Tibet.
   • This creates strong upward motion over Tibet
3. Strengthening of Indian low pressure System
   • The thermal low over Tibet combines with the surface low over north-west India.
   • This intensifies the continental low pressure system increasing the land-sea pressure gradient.
4. Strong cross equatorial flow
   • The increased pressure gradient draws strong south-east trade winds across the equator (Trade winds of southern hemisphere).
   • After crossing the equator these are deflected rightward by the Coriolis force and become the south-west monsoon winds.
5. Development of Tropical Easterly Jet
   • The heating of Tibet Plateau contributes to the Tropical Easterly Jet in upper atmosphere between 10° to 15° N latitude and between south-east Asia to Africa.
   • The TEJ enhances upper layer divergence which supports strong convection and monsoon rainfall.
6. Strengthening of Mascarene High
   • Although the Mascarene High is not created by Tibet Plateau but it strengthening is done by the descending air which comes form Tibet.
   • In the higher troposphere of Tibet anti-cyclonic condition are develop from where wind diverges toward equator and after crossing the equator it descends over southern Indian Ocean, Mascarene High.
   • Strengthening of Mascarene High further intensifies PGF (pressure gradient force) between Indian Subcontinent and sea.
   • Surface wind blows towards equator and thereafter towards Indian Subcontinent and it creates a positive feedback and this cellular motion of the wind is called Koteswaram Cell.

What if Tibet Plateau not heated properly?

It leads to poor monsoon because

1. PGF between land and sea is poor
2. Weak Mascarene High
3. Weak Tropical Easterly Jet
4. Weak Somali Jet as it is outcome of strong Mascarene High
5. Sometime northward shifting of sub-tropical Westerly Jetstream is also delayed.

Somali Jet

It is a strong low level Jetstream at the altitude of 1 to 1.5km. It blows along with eastern coat of Africa and after crossing equator it turns rightward to reach Indian Subcontinent.

Mechanism of formation

1. Strong Pressure Gradient
   • Mascarene High develops strong high pressure.
   • At the same time there is thermal low over north-west India and Tibet plateau.
2. Cross Equatorial Flow
   • Air naturally moves from high pressure to low pressure.
   • South-East Trade winds cross the equator.
3. Coriolis Force
   • After crossing into northern hemisphere the winds are deflected to the right.
   • The south-east trade become south-west trade wind or south-west monsoon.
4. Channelling along Somalia
   • The east African highlands guide and accelerates these winds along the Somalia coast.
   • This produces a narrow fast moving air current called Somali Jet.
   • The powerful Somali Jet blowing at the altitude of 1 to 1.5km blows over Arabian Sea to reach over Indian Subcontinent and influences the winds to absorb more moisture and cause good rain over India.

Indian Ocean Dipole

Indian Ocean Dipole is an ocean atmosphere coupled phenomena characterized by the difference in sea surface temperature between the western equatorial Indian Ocean near east Africa and eastern equatorial Indian Ocean near Indonesia. It was first described by NH Saji and independently by Toshio Yamagata in 1999.

Mechanism of IOD

• Normal Condition
  • SST (sea-surface temperature) is warmer near Indonesia than near east Africa. Warm water causes low pressure and rising air over Indonesia whereas cooler western Indian Ocean has relatively high pressure. The surface wind blows from west to east maintain the warm pool of water in eastern Indian Ocean.
• Positive IOD
  • SST becomes warmer in the western Indian Ocean
  • SST becomes cooler near Indonesia due to strong upwelling.
  • Low pressure shift towards east Africa.
  • Rising air occurs over the western Indian Ocean.
  • Sinking air develops over Indonesia.
  • Surface winds weakens along the equator.
  • Impact on India
    • Stronger southwest monsoon because it absorb more moisture. It receives normal to above normal rainfall in many parts.
• Negative IOD
  • Eastern Indian Ocean becomes warmer than normal.
  • Western Indian Ocean become cooler.
  • Strong convection develops near Indonesia.
  • Air sinks over the western Indian Ocean
  • Moisture transported towards India is weakened.
  • Impact on India
    • Weak southwest monsoon reduce rainfall and increase risk of drought.
    • It mostly associated with El-Nino

Madden Julian Oscillation

Basic Structure of MJO

MJO consists of two parts:-

1. Active Phase/Convection
   • Warm and moist air rises
   • Deep cumulonimbus clouds develop
   • Heavy rainfall occurs
   • Strong convection
2. Suppressed Phase
   • Air sinks/subsides
   • High pressure develop
   • Cloud formation decreases
   • Dry weather prevails

Mechanism of MJO

1. Warm Ocean Surface
   • Tropical ocean receives intense solar heating.
   • Sea surface temperature exceeds about 28°C, supplying abundant moisture.
2. Formation of Deep Convection
   • Moist air rises up
   • Condensation releases latent heat
   • A large convection cloud cluster develops
3. Upper Level Divergence
   • Rising air spreads outward in upper troposphere
   • It strengthens the convection
4. Eastward Movement
   • Atmospheric waves and wind interaction shift the convection system eastward across the tropics
5. Suppresses Phase Follows
   • Behind every active phase there is suppressed phase.
   • Cloud formation decreases rainfall decreases.

How does MJO influence Southwest Monsoon?

• MJO control active and break in monsoon
• Active phase over Indian Ocean causes strong convection and strengthening of low pressure thus moisture transfer increases and widespread rainfall occurs across India.
• While, suppressed phase over Indian Ocean is dominated by descending air thus poor rainfall. It causes "Break Monsoon" conditions.
• During the active phase Northern Indian phase become highly convective specially Bay of Bengal thus more low pressure system thus monsoon depression are formed. We know that monsoon rain in India is directly proportional to number of depression.
• Active phase of MJO strengthens cross equatorial winds, intensifies Somali Jet and increases moisture transport to the Northern Indian Ocean.
• Active phase of MJO pushes monsoon winds to reach India in advance/before date. e.g. 2025 monsoon reached India (Kerala) in May 6 days in advance.
• If in the suppress phase during onset of monsoon over Indian Ocean then the onset of monsoon is delayed.

Southern Oscillation

The southern oscillation is see-saw pattern of atmosphere pressure between Eastern Pacific (Tahiti) and Western Pacific (Darwin of Australia). It is one of two components of ENSO i.e. EL-Niño Southern Oscillation phenomenon and the other begin changes in the sea surface temperature (El-Nino and La-Nina).

Mechanism

• Normal condition
  • Pressure over Tahiti is high
  • Pressure over Darwin is low
  • Strong trade wind blows from east to west
  • Warm water accumulates near Indonesia and northern Australia.
  • Strong convection and rainfall occur over Western Pacific.
  • Cold water upwelling occurs off Peru and Ecuador result normal and good monsoon.
• Positive Southern Oscillation (La-Nina)
  • Pressure over Tahiti increases
  • Pressure over Darwin decreases
  • Trade wind become much stronger
  • Warm water is pushed further west
  • Strong convection over Indonesia and nearby regions.
  • Impact on India
    • Generally stronger and more than normal rainfall
    • Sometime it become excess rainfall.
• Negative Southern Oscillation (El-Nino)
  • Pressure over Tahiti decreases
  • Pressure over Darwin increases
  • Trade winds become weak
  • Warm water shifts eastward toward Peru
  • Convection moves to eastern Pacific (sometimes up to Central Pacific)
  • Impact on India
    • Weak Southwest Monsoon
    • High probability of drought
    • Reduce agricultural production
    • Increased heatwaves

El-Nino Modoki

El-Nino Modoki is type of El-Nino in which the maximum sea surface temperature warming occurs in the North Central Pacific instead of Equatorial Pacific near Peru or Ecuador which happen in the typical classical El-Nino. The word "Modoki" is a Japanese word which means "Similar but different". It was introduced by Japanese meteorologist and climatologist Toshio Yamagata in 2007

Mechanism

• Warm sea surface temperature in the Central Equatorial Pacific.
• The Eastern Pacific remains relatively cool.
• Rising air and deep convection shifts to the Central Pacific instead of the Eastern Pacific. It creates tripolar sea surface temperature patter:-
  • Cool temperature in the Western Pacific
  • Cool temperature in the Eastern Pacific
  • Warm temperature in the Central Pacific
• Thus water circulation become spilt into two circulation cell i.e. convection rises from Central Pacific down on the Western and Eastern Pacific.

Impact on India

• It weakens Southwest Monsoon but not always
• The impact depends strongly on the behaviour of IOD and MJO.

Southwest Monsoon

Mechanism of Origin

• During summer season strong low pressure area develop over Northwest India where atmosphere pressure falls up to 994 to 996 mb whereas, high pressure remains over Southern Indian Ocean i.e. 1020 to 1025 mb or hPa.
• Besides this due to apparent northward shifting of sun ITCZ also shifted northward as monsoon trough. This ITCZ attracts trade winds of southern hemisphere to cross equator. After crossing the equator it is deflected rightward by Coriolis forces and reaches over Indian Subcontinent.
• However while blowing over Northern Indian Ocean it is divided into two branches
  1. Arabian Sea Branch
  2. Bay of Bengal Branch

Arabian Sea Branch

• Arabian sea branch reaches to Kerala first and make first monsoon rain over there on 1^st June.
• Rain occurs along with western slope of western Ghats. The eastern slope falls in rain shadow area.
• By 5^th June it reaches to coastal Karnataka and by 10^th June to Mumbai. This way entire western coast receives good rainfall by 10^th June.
• Thereafter, this monsoon branch enter in Narmada and Tapi rift valley and goes deep inside to Madhya Pradesh.
• By 15^th June it rains entire Gujrat and moves northward to rain over Rajasthan.
• In Rajasthan eastern part receives good rain but western part does not because:-
  • Monsoon wind blow parallel to Aravalli
  • Condition of temperate inversion prevailing over Western Rajasthan, deserts.
• By 20^thJune it reaches to Delhi, Haryana plain where it joined by Bay of Bengal branch by 15^thJuly entire India covered.

Bay of Bengal Branch

Bay of Bengal branch is stronger than Arabian Sea branch because

1. Average temperature of Bay of Bengal is higher than Arabian Sea
2. Monsoon winds blow for a longer duration over Bay of Bengal before they hit continents thus have high amount of moisture.

• Bay of Bengal branch brings first monsoon rain India between 20^th to 25^th May on Andaman and Nicobar island.
• By 5^thJune it covers Northeast India.
• By 10^th June covers Telangana, Odisha, West Bengal and Andhra Pradesh.
• By 15^th June Chhattisgarh, Bihar, Jharkhand, Eastern Uttar Pradesh.
• By 20^thJune Central India, Madhya Pradesh, Jharkhand, Western Uttar Pradesh.
• By 25^thJune it joins Arabian Sea branch in Delhi-Haryana-Punjab plains.
• By 15^thJuly entire India is covered.
• It keep raining over India up to first week of September. Thereafter, it start retracting.

Northeast Monsoon

Northeast monsoon also called retracting monsoon is a seasonal reversal of winds that occurs from September to December first week. It blows from land to the sea thus it does not rain except Tamil Naidu where it rains because moisture it absorb from Bay of Bengal.

Mechanism

• By late September, the sun appears to move south to equator.
• The Indian landmass begin to cool rapidly. At the same time Arabian sea and Bay of Bengal start getting warmer.
• ITCZ start shifting southward thus wind direction become northeast to southwest and it blows from land to the sea.
• Only some par to the northeast wind which blows over Bay of Bengal receives good amount of moisture and rains over Tamil Naidu and some parts of Andhra Pradesh like Nellore, Tirupati, etc.
• By the first week of December northeast monsoon leaves India.

Rainfall Distribution in India

The distribution of rainfall in India is mainly influenced by Southwest Monsoon i.e. June to September, Northeast Monsoon specially in Tamil Naidu, westerly disturbances and tropical cyclones which occur mainly in coastal areas. The average rainfall in India is 110 cm per annum. However, the rainfall distribution in India has high spatial and temporal variations.

Distribution of Rainfall

Factors Affecting Rainfall distribution

• Direction and strength of monsoon winds.
• Relief features such as Himalayas and Western Ghats.
• Large geographical area of country which strongly creates effect of continentality.
• Variation in the local temperature and local pressure gradient.
• Besides this regional/ spatial variation there is temporal variation also in the distribution of rainfall because India receives its 70 to 80% rain between June to September only.
• Westerly disturbances remain confined to the winter season and only North Indian Plain.
• Pre and Post Monsoon tropical cyclones effect only coastal areas.

Rainfall Variability

Rainfall variability refers to year to year fluctuations in the amount of rainfall receives at a place compared with its long term average. It is expressed as coefficient variability or CV

CV = $\frac{\mathrm{Standard\; Devation}}{\mathrm{Mean\; Rainfall}}\times 100$

• If the value of CV is low it means rainfall is reliable and uniform.
• If the value of CV is high rainfall is erratic and uncertain.

Spatial Pattern of Rainfall Variability in India

Why Does Rainfall Variability Differ?

1. Amount of Rainfall
   • Areas with high average rainfall generally have low variability e.g. Northeast India.
   • Areas with low average rainfall generally have high variability e.g. Western Rajasthan.
2. Monsoon Dependence
   • Regions depending on few monsoon events show greater fluctuations e.g. Western Rajasthan and Punjab.
3. Relief
   • Region with high relief receives consistent orographic rainfall e.g. Western Ghats and Himalayas.
4. Dependency of monsoon on various climatic phenomena like IOD, MJO, El-Nino, etc.

Importance of Rainfall Variability

• High variability increases the risk of droughts and crop failure.
• It affects food security.
• It exerts heavy pressure on groundwater resources.
• It highlights the need for irrigation, crop diversification, watershed management and climate resilient agriculture.

Koppen's Classification of Climate of India

Merits of Koepen's Classification

• Objective and scientific classification based on measurable climate data.
• Useful for studying vegetation, agriculture, and climate change.
• Enable comparison of climates across different regions of the world.

Limitations of Koepen's Classification

• Does not adequately explain India's monsoon dynamics.
• Local influences such as altitude aspect and western disturbances are not fully captured.
• Climatic transition are gradual whereas the classification uses fixed boundaries where which not realistic.

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