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Text of Introduction - INFLIBNET ... Introduction western half of the Ladakh in Jammu-Kashmir. Severe heat...

  • Chapter 1

    Introduction

    In simple words, climate of a place is known as the average of the weather

    components including the frequency of extreme events. As per the current practice

    weather parameters over a period of at least 30 years constitutes the climate. There are

    continuous interactions between the components of climate system such as atmosphere,

    biosphere, cryosphere, land and ocean. Natural variation in climate can occur due to

    volcanic eruption, continental drift and built up of mountains, changes in tilt angle of

    earth’s orbit, sun’s radiation intensity and the slow but large scale ocean circulation etc.

    However, changes in greenhouse gas (GHG) concentrations, aerosol emissions and

    urbanization give rise to the anthropogenic climate change. Today, climate change is one

    of the major issues on the earth system and its impact has already been realized in several

    geographical locations and sectors in the society (IPCC 2007). There is a worldwide

    concern about the anthropogenic climate change, particularly during the last two decades.

    Most important visible changes are those in temperature, snow/ice melt and precipitation

    extremes. Before understanding any scientific study on Indian climate, it is essential to

    know some of the important diversities in Indian weather and climate.

    1.1 Weather and climate of India

    India is a south Asian country which lies to the north of the equator between 8.4o

    and 37.6o north latitude and 68.7o and 97.25o east longitude. This tropical country is

    surrounded by water bodies on three sides, Arabian Sea towards the West, Bay of Bengal

    towards the East and Indian Ocean towards the South. India is having unique

    geographical features with complex topography. Mountain range such as the Himalayas

    broadens in the north and northeast. The Vindhyas separate the Indo Gangetic plain from

    the Deccan Plateau. The Satpura, Aravalli and Sahyadri cover the eastern fringe of the

    TERI University‐Ph.D. Thesis, 2012                                        1 

  • Introduction 

    West Coast plains. The coasts of southern parts of India are known as Western and

    Eastern Ghats. Eastern Ghats are irregularly scattered and forms the boundary of the East

    Coast plains. Tibetan plateau towards the north of the foothills of Himalayas also

    influences Indian summer monsoon. On the northwest part of India, Thar desert extends

    from the edge of the Rann of Kachchh of Gujarat up to the frontier of Rajasthan.

    Classification of climate for any region is the organization of climate information

    for analysis and communication. India is a vast country with diversities in its weather and

    climate. Wladimir Köppen, a German botanist and climatologist is most widely known

    for the descriptive climate classification system which he first proposed in 1884. After

    several modifications, world map of climatic classification by Köppen was introduced in

    1936. It combines the average of annual and monthly temperature and precipitation, and

    the seasonality of precipitation. According to the Köppen climate classification system,

    Indian climate can be divided into six major subtypes. Desert or arid climate regions are

    in the west and beyond that there is semi-arid climate. Semi-arid climate can also be

    observed between Eastern and Western Ghats. Alpine tundra and glaciers are found in the

    north and over the Himalayan ranges. Humid subtropical regions are in the north of

    central and eastern India. Tropical wet climate regions are the Western Ghats and Island

    territories. Parts of peninsular India experience tropical wet and dry climate.

    In India there are four distinct seasons, pre-monsoon (April-May), summer

    monsoon (June-July-August-September), post-monsoon (October-November) and winter

    (December-January-February). India is a tropical country with hot weather conditions

    that varies from region to region. In the pre-monsoon months vast land portion of India is

    dominated by intense solar heating which leads to heat wave conditions. Similarly cold

    wave conditions during winter season occur due to the intense high pressure cells and

    passing of western disturbances. There is no absolute definition for heat or cold wave

    events. The term is relative to the average weather condition of a region of study.

    According to a study by Raghavan (1967), severe cold waves develop very often in situ

    within the country itself and account for the higher incidence in certain isolated regions.

    Irrespective of the intensity, severe cold wave are mostly confined to either eastern or the

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  • Introduction 

    western half of the Ladakh in Jammu-Kashmir. Severe heat waves are also not so far

    been observed to migrate from the neighboring countries Raghavan (1966). They develop

    in situ within the country itself and expand from West Pakistan to affect Northwest India.

    He further concluded that available statistics do not suggest any periodicity in the

    incidence of extreme temperature conditions in any region or in the country as a whole.

    He considered the persistency of the waves over different subdivisions where they

    dissipate or wherefrom they migrate to adjacent regions. In India more than 70% of its

    population relying on agriculture directly or indirectly and thus the impact of extreme

    weather events is critical. In the last two decades India has been affected by successive

    extreme temperature events, monsoons flooding and droughts (De et al. 2005). Snow is

    also an important component of the hydrological cycle. Major contribution of many parts

    of the world snow is in the form of precipitation or total annual water supply. The

    allocation of limited water resources has significant economic and policy consequences.

    Eurasian, Tibetan and Himalayan snow in winter and spring may affect the Indian

    summer monsoon circulation and rainfall. It may influence both river basin runoff and

    climate change dynamics. It has been revealed that snow cover/depth variations during

    winter in Eurasia are not only associated with monsoon rainfall in Southeast Asia but also

    recognized as an effective source of freshwater flowing to the Arctic Ocean (Rogers et al.

    2001), and may thus be linked to the global thermohaline circulation (Walsh et al. 1998),

    which is a major determinant of the global climate.

    In India two major monsoon systems are observed, southwest/summer monsoon

    from June to September and northeast/winter monsoon from October to November.

    Monsoon is produced by differences between land and sea temperatures in eastern and

    southern Asia. It is a seasonally varying wind system, e.g. in the Indian Ocean winds are

    southwesterly with moist air and high precipitation in summer, northeasterly with dry air

    and clear skies in winter. During the post-monsoon months northeast monsoon dominates

    over the southern parts of Peninsular India particularly in Andhra Pradesh, Rayalaseema,

    Tamilnadu and Pondicherry. The principal components of northeast monsoon system are

    Siberian high pressure system, northeasterly lower tropospheric flow, wind surges carried

    by the northwesterly monsoon flow along the western shores of South China Sea, the

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  • Introduction 

    monsoon trough located near to the north of the equator in December and south of the

    equator in January and February, the west Pacific high and the subtropical jet stream of

    winter. At the beginning of October, a trough of low pressure develops over the south of

    Bay of Bengal and equatorial maritime air moves towards the southern India that causes

    northeast monsoon rainfall (Kripalani and Kumar, 2004). They found that Indian Ocean

    dipole positive phase also enhances the rainfall activity of northeast monsoon and

    negative phase suppresses. Dhar and Rakecha (1983) and Singh and Sontakke (1999)

    identified enhancement in northeast monsoon rainfall during El Niño events.

    1.2 Indian summer monsoon main features

    The weather and climate of India are dominated by the summer monsoon, which

    returns with remarkable regularity in each summer and provides the rainfall needed to

    sustain over a billion of people. The vastness of Indian sub-continent and the unique

    configuration of the east African highlands and the Tibetan plateau mean that the Indian

    summer monsoon is the most vigorou