The Indian Summer Monsoon:Past, Present and Future

Some basic facts• 1.13 billion (113 crore)people - one-sixth of the world's

population - live in a country one-third the size of the U.S. Over 37% live below the poverty line.

• Population projected to rise to 1.8 billion (180 crore) by 2050.• World’s eleventh largest economy and second most rapidly

growing economy with GDP growth rate last year of 6.7%.• Sustained by annual rainfall of around 1100mm, 80% of which

arrives in the summer.• Agriculture accounts for nearly 20% of the GDP and employs

over 50% of the total workforce.• 60% of agricultural production is rainfed and hence vulnerable.

Latitude and Longitude

Geographical Zones1. The North Frigid Zone, north of the Arctic Circle

2. The North Temperate Zone, between the Arctic Circle and the Tropic of Cancer

3. The Torrid Zone, between the Tropical Circles

4. The South Temperate Zone, between the Tropic of Capricorn and the Antarctic Circle

5. The South Frigid Zone, south of the Antarctic Circle

Zones

Zones

Zones Contd.

Tropic of Cancer

States of Gujarat, Rajasthan, Madhya Pradesh, Chhatisgarh, Jharkhand and West Bengal & The State of Mizoram

What are Monsoons?

• ‘Monsoon’ means ‘season’, and describes a complete reversal of wind regimes during the seasonal cycle. Monsoons are characterised by a pronounced rainy season.

• Monsoons are driven by changes in the distribution of heating driven primarily by the seasonal cycle of the sun. A thermal contrast between land and sea is required to set up a monsoon.

• In winter, the wind blows from the cold land over the warm sea. In summer, the warm land pulls in the wind from the ocean like a massive sea breeze.

• Once established, the positive feedback between the circulation and latent heat release in the rain clouds maintains the monsoon

How is it caused?

Movement of the ITCZThe point of max insolation alters throughout the year and the ITCZ migrates accordingly; north in June (dragging low pressure over India) and south in December (dragging high pressure over central Asia).

The Intertropical Convergence Zone (ITCZ), known by sailors as the doldrums, is the area encircling the earth near the equator where the northeast and southeast trade winds come together.

How is it caused?Differential heatingSummer: Intense heating of

land mass. Oceans take longer to warm. This generates pressure differences leading to SW winds (Em and Tm air masses).

Winter: Land cools rapidly. Ocean retains warmth. Pressure change is reversed and winds move from NE (Tc and Pc from desert).

Pre-Monsoon Land/Sea Temperature contrasts

Nov./Dec.

May/June

How is it caused?

Summer: SW Monsoon Winter: NE Monsoon• ITCZ dragged North• Low pressure over India• Land warmer than seas• Coriolis deflects northerly

winds to the East• Heavy rains move North

along west and east coasts• East rains deflected west

due to Himalayas

• ITCZ dragged South• High pressure over C.Asia• Land cools rapidly• Coriolis deflects southerly

winds to the West• Dry air dries further as it

moves over Tibetan Plateau• Air warms as it descends to

the Indian plains

Winds near the surface (925hPa)

Winter

Summer Asian Monsoon

Indian Monsoon is part of a much larger circulation, the Asian Monsoon

How is it caused?

• Pattern of rainfall in summer monsoon is altered by topography. Western Ghats create rain shadow in central India. Himalayas have same effect for central Asia.

• Some areas of SE India and Sri Lanka receive rainfall in Winter as winds pass over Bay of Bengal and gain moisture

Rainfall (mm/day)

Winter

Summer

Arrival and retreat of the monsoon rain

• There is a stepped progression and recession of the monsoon rains as they cross India.

• Sri Lanka usually has monsoon rainfall in early May whereas in Pakistan it is July.

• In winter, the retreat begins in September but will not reach Southern India until November

Climatological Onset Dates

Monsoon sweeps north and west

15 July

1 July 15 June

10 June

5 June 1 June

1 June

Possible Players in Monsoon Variab ility (+++ Level of confidence/knowledge)

• El Nino/Southern Oscillation (+++)

• Eurasian and Himalayan snow amounts (+)

• Indian Ocean sea surface temperatures and heat content (+)

• Intra-seasonal variability e.g. active/break cycles (++)

El Nino

• El Niño is defined by prolonged warming in the Pacific Ocean sea surface temperatures when compared with the average value. The accepted definition is a warming of at least 0.5 °C (0.9 °F) averaged over the east-central tropical Pacific Ocean. Typically, this anomaly happens at irregular intervals of two to seven years, and lasts nine months to two years.[5] The average period length is five years. When this warming occurs for only seven to nine months, it is classified as El Niño "conditions"; when it occurs for more than that period

•  • El Niño's warm rush of nutrient-poor water heated by its eastward passage in the Equatorial Current, replaces

the cold, nutrient-rich surface water of the Humboldt Current. When El Niño conditions last for many months, extensive ocean warming and the reduction in easterly trade winds limits upwelling of cold nutrient-rich deep water, and its economic impact to local fishing for an international market can be serious.[8]

• More generally, El Niño can affect commodity prices and the macroeconomy of different countries - and not always for the worst. It can constrain the supply of rain-driven agricultural commodities; reduce agricultural output, construction, and services activities; create food-price and generalised inflation; and may trigger social unrest in commodity-dependent poor countries that primarily rely on imported food.[9] A University of Cambridge Working Paper shows that while Australia, Chile, Indonesia, India, Japan, New Zealand and South Africa face a short-lived fall in economic activity in response to an El Niño shock, other countries may actually benefit from an El Niño weather shock (either directly or indirectly through positive spillovers from major trading partners), for instance, Argentina, Canada, Mexico and the United States. Furthermore, most countries in the sample experience short-run inflationary pressures following an El Niño shock, while global energy and non-fuel commodity prices increase.[

La Nina

La Nina years

• During La Niña years, the formation of tropical cyclones, along with the subtropical ridge position, shifts westward across the western Pacific ocean, which increases the landfall threat to China.[3] In March 2008, La Niña caused a drop in sea surface temperatures over Southeast Asia by 2 °C. It also caused heavy rains over Malaysia, the Philippines, and Indonesia.[4]

Monsoons and climate change

• The key question lies with the ability of the affected nations to cope with the changes – India, Pakistan, Bangladesh, Myanmar

• Half of global population rely on annual monsoon to bring water for agriculture

• Variations of timing and intensity will affect billions of people

• Frequency has increased (10%) since 1950s, severe rains have doubled

• Impacts of heavy rains – flash floods and landslides – if these intensify the agriculture suffers

• End of 21stC temps up 3C – some areas get more rain, others suffer drought

• Increases in cholera, hepatitis, malaria

What is the Future

• Are we contributing in any ways• What is the action plans of the Govt• What are issues we can deal

Indian Rivers Inter-link

What we can do• Plant Drought Resistant Crops: It is an important thing for farmers to find out

what grows well locally. Examples of drought-resistant crops are: cassava, finger and pearl millet, amaranth species, sorghum,, potatoes, cassava, moringa, paw paw among others. These all do relatively well, even if there is a drought.

• Conserve Water: Anyone can do this by capturing rainwater on rooftops or using low cost drip irrigation. Use soil conservation techniques such as soil mulching.

• Plant a variety of Local crops: planting a range of drought-resistant crops, reduces the chances for total loss during drought. It is also very important to choose local crops. These should be crops, that are familiar, like Cassava, which is readily available, and have been grown locally for generations. These are equal and at times superior to imported crops. Local crops are typically hardy, and they are adapted to the local climate, thus making them very valuable.

• Plant trees

Thank you