Indian monsoon

Aquifer

Definition: large body of permeable material where groundwater is present and fills all pore space. Several aquifer units are combined into aquifer systems based on some common characteristic like rock type or river basin.

Based on the hydro geological characteristics, India has been classified into 14 principal aquifer systems and 42 major aquifers, Alluvium being the major aquifer system in India.

Need to demarcate aquifers to plan sustainable Aquifers:

• Intensive and unregulated groundwater pumping in many areas causing rapid and widespread groundwater decline.

• Estimating the quantity and quality of ground water in an aquifer.

• Assessment of sustainable level of ground water extraction.

• Making the country climate change resilient.

There has been a paradigm shift from “groundwater development” to “groundwater management”. An accurate and comprehensive micro‐level picture of groundwater in India through aquifer mapping and demarcation will enable robust groundwater management plans at the appropriate scale to be devised and implemented for this common‐pool resource.



Benefits

Scientific

• Information of water bearing formations.

• Assessment of water bearing capacity of different areas.

• Managing aquifer quality.

• Demand‐Supply analysis.

• Strategies for Sustainable Management.

• Precise assessment of functional wells for agriculture, industries, drinking water purposes.

• Formation of Aquifer Management Unit.

• Preparation of Aquifer Management Plans for sustainable groundwater management.

Social:

• Will enable involvement of community and stakeholders which in turn would enable states to manage resources in an efficient and equitable manner..

• Will result in better understanding of aquifers at community level. Scientific inputs and traditional wisdom together would ensure sustainable groundwater resource management.

• Would ensure sustainable cropping pattern, thereby contributing towards food security.

• Will help achieving drinking water security, improved irrigation facility and sustainability in water resources

development in large parts of rural and urban India.



Steps taken by the Government

• Hydro geological studies by Central Ground Water Board to decipher the extent, characteristics, yield potential and development prospects of important hydro geological units in the country.

• collaboration with international agencies to carry out water balance studies

• Project for Aquifer Mapping and Management (NAQUIM) in 2012‐ using advanced technologies like heli‐borne geophysical surveys , sophisticated softwares like RockWorks, ARC GIS, Modflow, Map

Info etc. to prepare Management plans.

The final objective is to prepare Management Plans, in consultation with stakeholders and State Governments, which will identify the recharge and other measures to replenish the declining trend of groundwater and lay the course for their sustainable use and development.



Rainfall





India ‐ average annual rainfall is about 125 cm



Temporal variation: as per an annual cycle of seasons. ‐ four seasons.

Cold Weather Season:

• Little rainfall in some parts of India.

• Some weak temperate cyclones from the

Mediterranean Sea cause rainfall in north‐western

India, called Western Disturbances.

Hot weather season

• A sudden contact between dry and moist air masses gives rise to local storms which are associated with

torrential rains.

Southwest Monsoon season

• Over 80% of the annual rainfall‐ in the four rainy months of June to September.

• The monsoon burst in the first week of June in the coastal areas of Kerala, Karnataka, Goa and Maharashtra while in the interior parts of the country; it may be delayed to the first week of July.

• Monsoonal rainfall largely governed by relief or topography and rainfall has a declining trend with

increasing distance from the sea.

Retreating Monsoon

• By the end of September, the monsoon becomes weak ‐ southward march of the sun.

• North India ‐ dry weather

• rain in the eastern part of the Peninsula.



Spatial Distribution

Areas of High Rainfall (Over 200cm):

• along the mountain ranges obstructing the approaching moist winds, like the west coast, as well as in the sub‐Himalayan areas in the NE

Areas of medium Rainfall (100‐200 cm):

• Southern parts of Gujarat, east Tamil Nadu, northeastern Peninsula covering Orissa, Jharkhand, Bihar, eastern Madhya Pradesh, northern Ganga

plain along the sub‐Himalayas and the Cachar

Valley.

Areas of low Rainfall (50‐100 cm):

• Most of the regions having the effect of continentality like Western Uttar Pradesh, Delhi, Haryana, Punjab, Jammu and Kashmir, eastern

Rajasthan, Gujarat and Deccan Plateau.

Areas of inadequate Rainfall (Less than 50 cm):

• These are arid regions lying in the interior parts of the Peninsula, especially in Andhra Pradesh, Karnataka and Maharashtra, Ladakh and most of western

Rajasthan.



In the north India, rainfall decreases westwards and in

Peninsular India, except Tamil Nadu, it decreases eastward.



Changing pattern of rainfall in India: changing in terms of intensity, duration, frequency and spatial distribution:

• Rainfall extremes have increased threefold over the last few years.

• The frequency of floods in northwest and northeast while rainfall deficit in south has increased.

• The onset of the monsoon has been delayed due to a regime shift in climate i.e. from a weak to a strong El Niño period.

• Monsoons ‐ ending sooner reducing the length of the rainy season.

• Monsoon seasons ‐ witnessing random ‘break periods’ when there is little to no rainfall.



Though it’s difficult to attribute exact reasons for changing pattern, the following factors have affected the Monsoon pattern:

• The ripple effects of global warming and climate change

• Frequent El‐Nino and La‐Nina, the Indian Ocean Dipole and the Atlantic Nino

• Break periods are associated with rainfall systems moving northwards from the equatorial region.

• The high rate of deforestation



Thus it becomes imperative for India to work towards restoring the balance of nature in collaboration with other countries, so that monsoon pattern doesn’t change permanently.



During the monsoon, average rainfall in Karnataka is more than Maharashtra and Kerala.

• Mountain topography in Karnataka is broader than the narrow topography of Maharashtra. Due to greater width of mountains, rain bearing winds have to necessarily travel a longer distance and have more time for the drops to coalesce and precipitate as rainfall, resulting in higher rainfall.

• In contrast, narrow width of the Ghats in Maharashtra allows rain‐bearing wind to cross over to leeward side rapidly before precipitation can occur.

• In Kerala, the Ghats are in form of isolated mountains, where rain‐bearing winds can easily cross

over to leeward side through gaps in between

without precipitation occurring.



Ghats of Karnataka have gentle sloping mountains, compared to steep slopes of the Ghats in Maharashtra and Kerala. Air parcel will retain its energy and speed for a longer time when slope is gradual. This will provide sufficient vertical motion to cloud droplets to grow by collision– coalescence process and

hence form precipitation. Characteristic features of monsoon rainfall

Variability: percentage change from the mean values of rainfall at a place.

• Major cause of floods and draughts in an area. may occur because of o global (like El‐Nino, IOD) or

o regional (like positioning of Jet Streams)

o local (like areas where two monsoon branches meet) factors.

• Variability < 25% ‐ Western coasts, Western Ghats, Eastern plains of Ganga through North East, Northeast part of peninsula (Avg. Annual rainfall > 100 cm).

• Variability > 50% ‐ Western Rajasthan, Northern part of J&K, interior parts of the Deccan Plateau (Avg. annual rainfall < 50 cm).

• Rest of India has a variability of 25‐50% and these areas receive an annual rainfall of 50‐100 cm.

• Sudden Break: During South‐West monsoon period after having rains for a few days, if rain fails to occur for one or two weeks, it is known as break in monsoon. Due to different reasons‐

• In the northern India rains are likely to fail if the rain bearing storms are not very frequent along the monsoon trough.

• ITCZ gets stuck on Himalayan foothills due to its interaction with the Sub‐tropical jet. causes breaks over north India, while causing incessant rains in hills

• Over the West Coast, the dry spells are associated with days when winds blow parallel to the coast.

Variability of rainfall plays a

determining the cropping pattern

• Cropping pattern refers to the proportions of area under different crops at a particular period of time. crucial role in

in India as

variability of rainfall and amount of rainfall are inversely linked.

• Areas of high variability are flood or drought prone. Hence these are not agriculturally well developed regions. Availability of irrigation in some areas can compensate in times of scarcity but problem of floods

is still not addressed.

Cropping pattern

• areas with less variability‐ Monoculture of Rice, Tuber crops, plantation crops

• areas of medium variability‐ mixed cultivation is often practiced. Rice is grown if sufficient rainfall is received in September, otherwise millets are natural priority. Wheat is the principle Rabi crop

• areas of high variability‐ millets, jowar, bajra and ragi. Mixed cropping is very common in which pulses are mixed with cereals. Groundnut is an important commercial crop grown in dry areas.





















EL‐Nino, Madden Julian Oscillation and Indian Ocean Dipole:
ENSO and its influence on Indian Monsoon:
• The El Nino Southern Oscillation (ENSO) is a scientific term that describes the fluctuations in sea surface temperature and air pressure in the East‐Central Equatorial Pacific, and its impact on normal Walker cell. It consists of El Nino and La Nina events
• The Walker cell of South Pacific plays a very important role in the Indian Monsoon. During normal Walker Cycle, rising limb of Australia is coupled with sinking limb of Mascarene High, which strengthens the monsoon.
• During El Nino, sea surface temperatures around northern Australia are cooler than normal. The Walker Cell weakens or reverses and thus, weakens the Mascarene high pressure. This causes weakening of Indian Monsoon.
• During LA‐Nina, sea surface temperatures around northern Australia are warmer than normal. The Walker usually becomes very strong, and thus weakens the Mascarene high pressure. This causes the strengthening of Indian Monsoon.
• The El Nino‐Southern Oscillation (ENSO) is a recurring climate pattern involving changes in the temperature of waters in the central and eastern tropical Pacific Ocean.
• El Nino and La Nina are the extreme phases of the
ENSO cycle.
 

 El Nino
• Phenomenon of warming of the ocean surface, or above‐average sea surface temperatures (SST), in the central and eastern tropical Pacific Ocean is known as El Nino.
• The low‐level surface winds, which normally blow from east to west along the equator (“easterly winds”), instead weaken or, in some cases, start blowing the other direction (from west to east or “westerly winds”).
• This reversal of winds creates unusual warming and low pressure near the Peruvian Coast, and causes
heavy rainfall.
La Nina
• Phenomenon of cooling of the ocean surface or below‐average Sea surface temperatures (SST), in the central and eastern tropical Pacific Ocean is known as La Nina.
• The normal easterly winds along the equator become even stronger.
• This situation causes heavy rainfall (monsoon) on western Pacific areas.
Effects of El‐Nino and La‐Nina on India’s climate
• For India, El Nino during winter results in development of warm conditions.
• During summer, it leads to dry conditions and deficient monsoon, leading to droughts and water scarcity.
• Whereas La‐Nina brings rains and stronger monsoon in India, it may cause flood like situation in coastal areas.
• El‐Nino and La‐Nina are complex unpredictable phenomenon and Agriculture being the important occupation, climatic changes due to these are grave
for India.
Conclusion
• Research and studies has suggested that, El‐Nino and La‐Nina do not always affect the climate of India severely. Some other ocean atmospheric phenomena such as Indian Ocean dipole also impact the monsoon.
• Climate change has also adversely affected India’s climate. Global and national efforts such as NDCs, if implemented properly, can bring the stability to the fast changing climatic conditions


Madden‐Julian Oscillation
 (MJO) and its influence on Indian Monsoon:
• deep convection coupled with atmospheric circulation, moving slowly eastward over the Indian and Pacific Ocean.
• Each cycle lasts 30–60 days. It involves variations in wind, sea surface temperature, cloudiness, and
rainfall.
• As it moves, strong MJO activity splits planet into two — one in which the MJO is in active phase & above average rainfall, and the other in which it suppresses rainfall.
• The effect witnessed mainly in the tropical region. An active MJO through the Indian Ocean strengthens the monsoon and results in very good rainfall in most parts of the country. 
Indian Ocean Dipole (IOD) and its influence on Indian
Monsoon:
• IOD is an atmosphere‐ocean coupled phenomenon in the tropical Indian Ocean, characterised by a
difference in sea‐surface temperatures.
• A positive IOD occurs when the sea surface temperatures> than normal in the Arabian Sea and    < than normal in the tropical eastern Indian Ocean. When the reverse is the case, a negative IOD is said to have developed.
• During positive IOD the combined effect of Arabian sea evaporation and Mascarene high pressure strengthen the monsoon activity over the Indian subcontinent. 
• Also, fewer breaks in monsoon conditions during early IOD events. A positive IOD also minimize the impact of El Nino on Indian monsoon.