Climate of India

Warmer Arabian Sea behind more severe and frequent cyclones

Context: Behind extremely severe cyclone Biparjoy’s evolution is a gradual but undesirable change in the nature of the Arabian Sea: it was always relatively cooler compared to the Bay of Bengal in the north Indian Ocean.

Why traditionally West Indian Ocean experienced less number of tropical cyclones?

The ratio between Arabian Sea (A.S) and Bay of Bengal (B.O.B) has been 1:4 in terms of yearly cyclones because of the following factors:

Average temperature of B.O.B is higher than A.S. B.O.B is a warm pool region. On the other hand A.S has higher salinity and lower temperature which is disadvantageous for cyclone formation.
B.O.B has abundant water availability due to continuous influx of water from large rivers like Ganga, Brahmaputra etc. This freshwater influx makes it further impossible to mix with the cooler water below
Shape of the land around B.O.B weakens the wind speed thus allowing the winds to spin faster.
B.O.B also experiences the offshoots of tropical cyclones from Pacific-ocean.

On the other hand, Arabian Sea is calmer as stronger winds hand Arabian Sea is calmer as stronger winds help dissipate the heat and lack of constant fresh water helps the warm water to mix with the cool water underneath, reducing the surface temperature.

Changing nature of Arabian Sea:

Sea surface temperatures over the Arabian Sea have increased by 1.2 to 1.4 degrees C in recent decades compared to four decades ago.
According to a 2021 paper published in Nature, there is a significant increasing trend in the intensity, frequency, and duration of cyclonic storms (CS) and very severe cyclonic storms (VSCS) observed over the Arabian Sea during the study period, 1982 to 2019.
There is a 52% increase in the frequency of CS during the recent epoch (2001–2019) in the Arabian Sea, while there is a decrease of 8% in the Bay of Bengal, the paper highlighted.
Further, there has been an 80% increase in the total duration of cyclones in the Arabian Sea over two decades to 2021. The duration of very severe cyclones increased by 260% in the same period, the paper added.
The change in the Arabian Sea’s character has also led to more severe cyclones forming and sustaining over it which also means India’s west coast is now more vulnerable.

Climate change affecting frequency and intensity of tropical cyclones:

According to Council on Energy, Environment and Water (CEEW) India, in the last 50 years, has recorded a 12-fold surge in the number of associated cyclonic events such as extreme rainfall, floods, sea-level rise, and thunderstorms.

Increased sea surface temperature: Over the past 50 years, the global ocean has absorbed 90% of the excess heat generated due to man-made climate change leading to higher convection and rapid intensification of cyclones.
Rising sea level: on account of Antarctic melting has increased the moisture availability for cyclones.
Micro-climatic changes on land: Local heating of coastal land is pulled by adjacent ocean further heating it up.
Changing weather events: El-Nino and rising marine heat waves lead to prolonged warm periods over oceans by reducing the ocean upwelling.
Higher Atmospheric moisture: due to anthropogenic global warming increase cyclonic precipitation rates thereby increasing the frequency.
Changes in wind systems: Occasionally intense winds drive the low-pressure regions to other areas rising the frequency in those areas. Ex. Gulab cyclone shifted to Arabian sea from B.O.B.

IMD issues 4th heatwave alert in Konkan region, other Maharashtra districts.

Context: Heatwave conditions have been declared by the India Meteorological Department (IMD) in various regions of Maharashtra, including Mumbai, Palghar, Thane, Konkan, central Maharashtra, and Vidarbha. This is the fourth heatwave alert for the Konkan region and the first for the month of May, according to the IMD.

Heat Wave

A Heat Wave is a period of abnormally high temperatures, more than the normal maximum temperature that occurs during the summer season in the North-Western parts of India.
Heat Waves typically occur between March and June, and in some rare cases even extend till July.

Extreme temperatures and resultant atmospheric conditions adversely affect people living in these regions as they cause physiological stress, sometimes resulting in death.

Criteria for Heat Wave

IMD has given the following criteria for Heat Waves:

Two conditions which need to be satisfied:

Heat wave is considered if maximum temperature of a station reaches at least 40°C or more for Plains, 37°C or more for coastal stations and at least 30°C or more for Hilly regions. Following criteria are used to declare heat wave:
- Based on Departure from Normal
- Heat Wave: Departure from normal is 4.5°C to 6.4°C
- Severe Heat Wave: Departure from normal is 6.4°C
Based on Actual Maximum Temperature (for plains only)
- Heat Wave: When actual maximum temperature 45°C
- Severe Heat Wave: When actual maximum temperature 47°C

Declare heat wave, above criteria should be met at least in 2 stations in a Meteorological subdivision for at least two consecutive days.

Favourable Conditions for Heat Wave

Transportation/Prevalence of hot dry air over a region (There should be a region of warm dry air and appropriate flow pattern for transporting hot air over the region).
Absence of moisture in upper atmosphere (As presence of moisture restricts the temperature rise).
Sky should be cloudless (To allow maximum insulation over the region).
Large amplitude anti-cyclonic flow over the area.
Heat waves develop over Northwest India and spread gradually eastwards & southwards but not westwards (since the prevailing winds during the season are westerly to north westerly).

But on some occasions, heat wave may also develop over any region in situ under the favourable conditions.

What are the heat wave prone states over India?

Heat wave generally occurs over plains of northwest India, Central, East & north Peninsular India during March to June. It covers Punjab, Haryana, Delhi, Uttar Pradesh, Bihar, Jharkhand, West Bengal, Odisha, Madhya Pradesh, Rajasthan, Gujarat, parts of Maharashtra & Karnataka, Andhra Pradesh and Telengana. Sometimes it occurs over Tamilnadu & Kerala also. Heat waves adversely affect human and animal lives. However, maximum temperatures more than 45°C observed mainly over Rajasthan and Vidarbha region in month of May.

Impacts of Heat waves:

Heat waves affect each and every aspect of life. Following picture shows its multiple impacts in various dimensions:

Health Impacts of Heat Waves?

The health impacts of Heat Waves typically involve dehydration, heat cramps, heat exhaustion and/or heat stroke. The signs and symptoms are as follows:

♣ Heat Cramps: Ederna (swelling) and Syncope (Fainting) generally accompanied by fever below 39 degree C

♣ Heat Exhaustion: Fatigue, weakness, dizziness, headache, nausea, vomiting, muscle cramps and sweating.

♣ Heat Stoke: Body temperatures of 40 degree C or more along with delirium, seizures or coma. This is a potential fatal condition

To cope up with heat waves, IMD issues colour based warnings as follow:

Resilience Strategies For Extreme Heat

Identifying vulnerable populations and creating heat preparedness plans with all residents in mind, which may include steps like opening cooling centers during periods of extreme heat and adopting workplace heat stress standards.
Installing cool and green roofs and cool pavement to reduce the urban heat island effect.
Planting trees to provide shade and to cool the air through evapotranspiration.
Pursuing energy efficiency to reduce demand on the electricity grid, especially during heat waves.
Reducing concretisation in urban areas.
Adopting architectural designs to reduce heat load on built structures.
Emergency Measures: Democratization of access to public cool spaces in adverse heat waves. Ex. Metro Stations with air-cooled atmosphere should be made accessible to poor.
IMD should start measuring Heat Index and Wet Bulb Temperatures, which is a better indicator of heat.

Cyclone Mocha likely to develop over Bay of Bengal today: IMD

Context: A cyclone, which is most likely to swerve away from the Indian coast, is all set to develop over the southeast Bay of Bengal by Wednesday, the India Meteorological Department (IMD) said Tuesday.

Key facts about Mocha Cyclone

Once intensified, it is to be identified as Cyclone Mocha (pronounced as Mokha), a name suggested by Yemen.
India has dual cyclone seasons – pre-monsoon (April-June) and post-monsoon (October-December). Of these, the most cyclone-prone months are May and November.
In the IMD’s possible cyclone track released Monday, the storm is expected to move north-northwestwards, that is, away from India’s east coast.

How the naming of tropical cyclones are done?

In general, tropical cyclones are named according to the rules at regional level.

Northern Indian Ocean Names - Arabian Sea and the Bay of Bengal

The WMO/ESCAP Panel on Tropical Cyclones at its twenty-seventh Session held in 2000 in Muscat, Sultanate of Oman, agreed in principal to assign names to the tropical cyclones in the Bay of Bengal and Arabian Sea. The naming of the tropical cyclones over north Indian Ocean commenced from September 2004, with names provided by eight Members. Since then, five countries have joined the Panel.

The Panel Member’s names are listed alphabetically country wise.
The names will be used sequentially column wise.
The first name will start from the first row of column one and continue sequentially to the last row in the column thirteen.
The names of tropical cyclones over the north Indian Ocean will not be repeated, once used it will cease to be used again. The name should be new. It should not be there in the already existing list of any of the RSMCs worldwide including RSMC New Delhi.
The name of a tropical cyclone from south China Sea which crosses Thailand and emerge into the Bay of Bengal as a Tropical cyclone will not be changed.

The RSMC New Delhi Tropical Cyclone Center is responsible to name the tropical cyclones that have formed over the Bay of Bengal and the Arabian Sea when they have reached the relevant intensity.

All eyes on monsoon as cooler summer delays crucial pattern

Context: The large parts of country have logged temperatures that are up to 10°C lower than normal due to rains. An uncharacteristically cooler start to the summer, which is likely to persist for a few more weeks in several parts of the country, may hurt the arrival of the crucial monsoon season, weather scientists have said, at a time when the rainy season is expected to anyway be sapped by the Pacific warming phenomenon El Nino.

How lower temperatures are going to affect monsoon?

Relative thermal differences create pressure differences which play very significant role in the onset of monsoon.
More heating over northwest India helps with the onset of monsoon. When the ground heats up, especially in heatwave prone parts of northwest India (which includes Rajasthan, Haryana and Delhi), it creates an area of low pressure. There is something called the heat low which forms over northwest India.
Hence low temperatures over NW part will lower the advance of monsoonal winds.

What is heat low? What are its impacts on monsoon rainfall?

During the northward march of sun in northern hemisphere, the continent surrounding the Arabian Sea begin to receive large amounts of heat; not only in the form of radiation from sun, but also flux of heat from the earth’s surface into atmosphere.
As a result of this large input of power, trough of low pressure forms over this region.
Intense heat low acts as suction devise for moist air along the monsoon trough and to some extend related to good monsoon over India.
During weak heat low monsoon rainfall over India is greatly affected and results in deficient or scanty rainfall over vast area of country.

What is the role of monsoon trough?

Monsoon Trough is an elongated low-pressure area which extends from heat low over Pakistan to Head Bay of Bengal.
This is one of semi-permanent feature of monsoon circulation.
Monsoon trough may be a characteristic of east west orientation of Himalayan ranges and north south orientation of Khasi-Jaintia Hills.
Generally eastern side of monsoon trough oscillates, sometimes southwards and sometimes northwards.
- Southward migration results in active/vigorous monsoon over major part of India.
- In contrast, the northward migration of this trough leads to break monsoon condition over major part of India and heavy rains along foothills of Himalayas and sometimes floods in Brahmaputra river.

Shifting positions of monsoon trough	Impacts on distribution of rainfall across India
	• When we say that the trough is in normal position, that means it passes through Ganganagar, Allahabad, Calcutta and Head Bay. • This gives good rain to Central India. • As a effect of low formation and it’s passage along the trough, the strong wind currents form over the west coast. • These currents are blocked by Sahyadri mountains resulting in formation of offshore trough. • Hence due to this offshore trough west of coast of India receives good rain.
	• When the trough shifts to the south of it’s normal position, than the monsoon conditions are active giving excessive rainfall in central India and over the west coast of India due to offshore trough. • This position is best for monsoon condition giving rain to all over Peninsular India.
	• When the trough shifts to north of normal position it means that it shift to foothills of Himalayas giving good rain to Uttarakhand, Himachal Pradesh, Jammu and to all Northeast states of India. • This condition is known as “Break Monsoon” where rainfall activity over rest of India ceases.

The distribution and utilisation of water bodies in India

Context: A report released by Ministry of Jal Shakti has thrown light on the number of water bodies in India and what they are used for. The document is the first such census of water bodies in India. The census has identified 24,24,540 water bodies in India.

Definition of a Water body

All natural or man-made units bounded on all sides with some or no masonry work used for storing water for irrigation or other purposes (e.g. industrial, pisciculture, domestic/drinking, recreation, religious, ground water recharge etc.) will be treated as water bodies in this Census. These are usually of various types known by different names like tank, reservoirs, ponds and bundhies etc.
A structure where water from ice-melt, streams, springs, rain or drainage of water from residential or other areas is accumulated or water is stored by diversion from a stream, nala or river will also be treated as water body.

Information available on water bodies through following initiatives / Institutions

India - Water resource information system (India-WRIS) - Central Water Commission (CWC), Ministry of Jal Shakti.
Repair, Renovation and Restoration (RRR) of water bodies - Component of Pradhan Mantri Krishi Sinchayee Yojana (Har Khet Ko Pani)
“Jal Shakti Abhiyan - “Catch the Rain” The “Jal Shakti Abhiyan
Central Pollution Control Board (CPCB) CPCB
Mahatma Gandhi National Rural Employment Guarantee Scheme (MGNREGS)

Salient Features

First census of water bodies was conducted with reference year 2017-18 across the country in 33 States/UTs except Daman & Diu, Dadra & Nagar Haveli and Lakshadweep.

Classifications

During 1st census of water bodies, 24,24,540 water bodies have been enumerated in the country, out of which

59.5% (14,42,993) are ponds
15.7% (3,81,805) are tanks
12.1% (2,92,280) are reservoirs
remaining 12.7% (3,07,462) are water conservation schemes/check dams/percolation tanks, lakes and other water bodies

Location / Concentrations

Top five States in number of water bodies are as follows

Top five states in number of Ponds, Tanks and Lakes are as follows

Top five states in number of Reservoir, Water Conservation schemes are as follows

Out of the enumerated 24,24,540 water bodies, 97.1% (23,55,055) are in rural areas while 2.9% (69,485) are in urban areas.

Among all water bodies, 9.6% are located in Tribal areas, 8.8% in Flood prone areas,7.2 % under Drought Prone Area Programme (DPAP), 2.0 % in Naxal affected areas , 0.7% under Desert Development Programme (DDP)and remaining 71.7% water bodies are located in other areas.

Operational Status

Among these water bodies, 83.7% (20,30,040) are 'in use' whereas the remaining 16.3% (3,94,500) are not in use/non-functional on account of drying up, construction, siltation, destroyed beyond repair, salinity, industrial effluents etc.

Uses

Out of all 'in use' water bodies, major water bodies are reported to be used in Pisciculture followed by Irrigation and Ground water recharge.

Ownership

55.2% (13,38,735) water bodies are owned by private entities whereas 44.8% (10,85,805) are under public ownership.

Man made & Natural water bodies

78% are man-made water bodies whereas 22% are natural water bodies. Majority of man-made water bodies are earthen in nature and have original cost of construction upto Rs. 1,00,000.

Encroachment

• Among all 24,24,540 water bodies, 1.6% (38,496) water bodies are reported to be encroached. Majority of encroached water bodies are ponds followed by tanks.

• Water User Associations (WUA) has helped to a large extent in preventing encroachments .

Need for Water Bodies Census

The need for conducting a separate census of water bodies was pointed out by the Parliamentary Standing Committee on Water Resources on the subject “Repair, Renovation and Restoration of Water Bodies – Encroachment on water bodies and steps required to remove the encroachment and restore the water bodies”.
The Committee recommended that in order to enable an objective assessment of water bodies and their condition, there should be separate census of water bodies and thereby creating a Central database on water bodies. As recommended by the Standing Committee, the first Census of Water bodies was launched by Department of Water Resources, River Development & Ganga Rejuvenation in 2018-19 in convergence with the 6th Minor Irrigation (MI) census.

The use of water bodies data is also envisaged in the following fields:

The water bodies census data will serve as an authentic dataset for estimation of recharge of ground water.
Information obtained from MI Census and water body census will be highly useful in

implementation of the Atal Bhujal Yojana.

Block/ Gram Panchayat level data related to MI structures & water bodies will help the scheme personnel to convince the community of the actual groundwater conditions at the local level.
The information can be used for spatial analysis of distribution of abstraction structures Coordinates (Longitude and Latitude) and assessment of ground water draft.
There are several instances of water from bore wells being sold and bought at farm level, but specific reports are not available. The census may provide an opportunity to get ground information on this aspect and provide insights into farm level water trading. The information will be relevant to State Governments involved in farm level irrigation and water management.
Results of First Census of Water bodies will be immensely useful for planning and executing Pradhan Mantri Matsya Sampada Yojana (PMMSY).

The Department of Water Resources, River Development and Ganga Rejuvenation (DoWR, RD & GR), Ministry of Jal Shakti (MoJS), Government of India (GoI) has been conducting census of minor irrigation structures, quinquennially under the Centrally Sponsored Scheme “Irrigation Census” with 100% central assistance to States/UTs. The scope of Irrigation Census Scheme has been enhanced by launching the Census of Water Bodies in convergence with sixth Minor Irrigation Census which covers all types of water bodies in both rural and urban areas and aims to collect all the important parameters of the Water Body like type of use, status (whether defunct or in-use), storage etc.