BharatNotes
Overview
Heat waves, cold waves, lightning, thunderstorms, and hailstorms are among the deadliest natural hazards in India, collectively killing thousands every year. Unlike earthquakes or cyclones that attract global attention, these "silent disasters" often go underreported despite their devastating cumulative toll. Climate change is amplifying their frequency and intensity — the IPCC Sixth Assessment Report (2021--2023) projects that heat extremes that occurred once per decade in the pre-industrial era will occur 4.1 times per decade at 1.5 degrees Celsius warming and 5.6 times at 2 degrees Celsius. India, with its vast geographic and climatic diversity, is particularly vulnerable.
Heat Waves in India
IMD Criteria for Declaring Heat Waves
The India Meteorological Department (IMD) uses specific thresholds based on region and temperature departure to declare heat waves.
Baseline Temperature Thresholds (minimum for heat wave consideration):
| Region | Minimum Temperature Required |
|---|---|
| Plains | Maximum temperature >= 40 degrees Celsius |
| Coastal stations | Maximum temperature >= 37 degrees Celsius |
| Hilly regions | Maximum temperature >= 30 degrees Celsius |
Heat Wave Classification (once baseline is met):
| Classification | Departure from Normal | OR Actual Maximum Temperature |
|---|---|---|
| Heat Wave | 4.5 to 6.4 degrees Celsius above normal | >= 45 degrees Celsius |
| Severe Heat Wave | More than 6.4 degrees Celsius above normal | >= 47 degrees Celsius |
Prelims Alert: Heat waves are declared only when the above criteria are met at at least 2 stations in a meteorological sub-division for at least 2 consecutive days. The declaration is made on the second day.
Vulnerable Regions
India's heat wave corridor stretches across the northern plains, central India, and parts of the Deccan Plateau.
| State / Region | Vulnerability Factor |
|---|---|
| Rajasthan | Thar Desert — highest recorded temperatures in India (Phalodi: 51 degrees Celsius, May 2016) |
| Madhya Pradesh | Central location; Vidarbha region consistently records extreme heat |
| Uttar Pradesh | Dense population; high agricultural workforce exposure |
| Telangana | Semi-arid Deccan Plateau; rapid urbanisation increasing urban heat island effect |
| Odisha | Coastal-inland temperature gradient; high humidity amplifies heat stress |
| Bihar, Jharkhand | Heat wave corridor extending from Rajasthan through the Gangetic plains |
| Andhra Pradesh | Rayalaseema region — historically among the hottest zones |
Mortality and Impact
| Metric | Data |
|---|---|
| Deaths (2010--2023) | Over 11,000 heat-related deaths officially reported; actual figures likely far higher due to underreporting |
| 2015 heat wave | Over 2,500 deaths across Andhra Pradesh and Telangana alone — one of the deadliest on record |
| Economic impact | Reduced labour productivity (outdoor workers lose up to 30% efficiency), crop damage, increased electricity demand |
| Health effects | Heat cramps, heat exhaustion, heatstroke, dehydration, kidney disease, cardiovascular stress |
Urban Heat Island Effect
Cities experience temperatures 2--8 degrees Celsius higher than surrounding rural areas due to:
- Concrete and asphalt absorbing and re-radiating heat
- Reduced green cover and water bodies
- Waste heat from vehicles, air conditioning, and industry
- Dense construction blocking airflow
Wet-Bulb Temperature — The Survivability Threshold
| Concept | Detail |
|---|---|
| Definition | Wet-bulb temperature (Tw) measures the combined effect of heat and humidity — it reflects the lowest temperature a surface can reach through evaporative cooling |
| Theoretical limit | A Tw of 35 degrees Celsius has been identified as the upper physiological limit beyond which the human body cannot cool itself through sweating, leading to fatal hyperthermia within hours |
| Recent research | Studies from Penn State University (2022) show the actual danger threshold is significantly lower — 25--31 degrees Celsius Tw depending on age, activity level, and environment |
| Indian context | Coastal cities like Mumbai and Chennai face rising wet-bulb temperatures due to high humidity combined with rising heat |
Ahmedabad Heat Action Plan — A Model for India
The Ahmedabad Heat Action Plan (HAP), launched in 2013, was the first heat action plan in South Asia and has become a global model for heat-wave preparedness.
Background
In May 2010, Ahmedabad experienced a devastating heat wave with temperatures exceeding 46.8 degrees Celsius, leading to an estimated 1,344 excess deaths in a single week compared to the baseline. This catalysed the development of a structured heat action plan.
Key Components
| Component | Detail |
|---|---|
| Early warning system | IMD-based forecasting with colour-coded alerts (yellow, orange, red) disseminated through media, SMS, and community networks |
| Public awareness | Campaigns through print media, hoardings, pamphlets, and radio in local languages; training of community health workers |
| Inter-agency coordination | Protocol linking the municipal corporation, health department, emergency services, and hospitals |
| Healthcare preparedness | Training for healthcare professionals on diagnosing and treating heat-related illnesses; stockpiling of ORS and IV fluids |
| Cooling centres | Public buildings, temples, and community halls designated as cooling shelters during extreme heat |
| Mapping vulnerable populations | Identification of high-risk groups — outdoor workers, elderly, children, slum dwellers |
Impact
The HAP has been credited with averting approximately 1,190 deaths per year in Ahmedabad since its implementation (estimate by the University of Washington).
National Expansion
| Development | Detail |
|---|---|
| NDMA Guidelines (2016) | NDMA issued comprehensive guidelines for prevention and management of heat waves; recommended the Ahmedabad HAP as a template |
| State HAPs | Over 130 cities and 23 heat wave-prone states have developed heat action plans based on the Ahmedabad model |
| Odisha's pioneering role | Odisha prepared India's first state-level HAP in 1999, before Ahmedabad's city-level plan |
Exam Tip: For GS3 Mains, the Ahmedabad HAP is an excellent case study for answers on disaster preparedness, urban governance, and climate adaptation. Mention: (1) early warning, (2) inter-agency coordination, (3) public awareness, (4) healthcare preparedness, and (5) measurable reduction in mortality.
Cold Waves in India
IMD Criteria for Declaring Cold Waves
| Classification | Criteria |
|---|---|
| Baseline | Minimum temperature of a station is 10 degrees Celsius or less (plains) or 0 degrees Celsius or less (hilly regions) |
| Cold Wave | Departure from normal: -4.5 to -6.4 degrees Celsius OR actual minimum temperature <= 4 degrees Celsius |
| Severe Cold Wave | Departure from normal: more than -6.4 degrees Celsius OR actual minimum temperature <= 2 degrees Celsius |
| Coastal stations | Cold wave when minimum temperature departure is -4.5 degrees Celsius or less and minimum temperature is 15 degrees Celsius or less |
Cold waves must meet criteria at at least 2 stations in a meteorological sub-division for at least 2 consecutive days.
Vulnerable Regions and Impact
| Region | Impact |
|---|---|
| North India (Punjab, Haryana, UP, Rajasthan, Delhi) | Severe cold waves every winter; dense fog; deaths among homeless and outdoor workers |
| Bihar, Jharkhand | Cold-wave mortality among rural poor; inadequate shelter |
| Central India | Occasional cold spells extending into MP and Chhattisgarh |
Fog-Related Disasters
| Type | Impact |
|---|---|
| Road accidents | Dense fog on national highways (especially NH-44/GT Road) causes multi-vehicle pileups every winter; visibility drops to near zero |
| Aviation disruption | Delhi's Indira Gandhi International Airport records hundreds of flight delays and diversions annually due to fog (December--January) |
| Railway delays | Northern Railways operates on reduced schedules during peak fog; cascading delays across the network |
| Health impact | Respiratory illnesses spike; hypothermia deaths among homeless; crop damage from frost |
Lightning — India's Deadliest Weather Hazard
Scale of the Problem
| Metric | Data |
|---|---|
| Annual deaths | Lightning kills approximately 2,000--2,500+ people per year in India — the single largest natural hazard killer |
| NCRB data (2022) | Lightning accounted for 2,887 of 8,060 deaths attributed to "forces of nature" — 35.8% of all natural hazard deaths |
| 53-year toll | Between 1967 and 2020, lightning caused 101,309 deaths in India |
| Most vulnerable states | Madhya Pradesh, Maharashtra, Odisha, Jharkhand, Bihar, West Bengal, Chhattisgarh |
| Most vulnerable groups | Farmers, herders, construction workers, and others working in open fields during monsoon |
Lightning Resilient India Campaign (LRIC)
| Feature | Detail |
|---|---|
| Launched | 26 March 2019 by the Climate Resilient Observing Systems Promotion Council (CROPC) |
| Goal | Reduce lightning deaths by 80% in 3 years |
| Progress | Over 60% reduction in lightning deaths within 2 years in pilot states; Andhra Pradesh and Odisha saw up to 70% reduction (2019--2021) |
| Methods | Early warning systems, lightning detection networks, mobile alerts (45-minute advance warning), community awareness campaigns, installation of lightning protection devices |
| Detection technology | Earth Networks Total Lightning Network (ENTLN) — a sensor-based detection network providing real-time lightning tracking and advance warnings |
Exam Tip: Lightning is often overlooked in disaster management answers. Mentioning it in GS3 Mains with specific data (2,000+ deaths/year, LRIC campaign, NCRB figures) demonstrates awareness beyond conventional disaster topics and impresses examiners.
Thunderstorms, Dust Storms, and Hailstorms
Thunderstorms
| Type | Region | Season | Characteristics |
|---|---|---|---|
| Nor'westers (Kal Baisakhi) | West Bengal, Assam, Bihar, Odisha | March--May | Violent thunderstorms with gusty winds (60--100 km/h), hail, and heavy rain; crucial for pre-monsoon moisture |
| Loo | North India (Rajasthan, UP, Punjab, Haryana) | April--June | Hot, dry, dusty wind blowing from the west/northwest; temperatures can exceed 47 degrees Celsius; causes heatstroke |
| Dust storms (Andhi) | Rajasthan, western UP | April--June | Sudden, violent dust storms with winds exceeding 80 km/h; reduced visibility to near zero; structural damage |
| Squall lines | Indo-Gangetic Plain | Pre-monsoon | Organised lines of thunderstorms moving rapidly; severe wind damage |
Hailstorms
| Feature | Detail |
|---|---|
| Vulnerable regions | Northwest India, central India, parts of Deccan Plateau |
| Season | Pre-monsoon (March--May) and post-monsoon (October--November) |
| Primary impact | Crop damage — hailstorms can destroy standing crops (wheat, pulses, horticulture) within minutes |
| Insurance link | Hailstorm damage is covered under the Pradhan Mantri Fasal Bima Yojana (PMFBY) as a localised calamity |
| Structural damage | Large hailstones damage roofs, vehicles, and greenhouses |
Climate Change Amplification
IPCC Projections
| Parameter | 1.5 degrees Celsius Warming | 2 degrees Celsius Warming |
|---|---|---|
| Frequency of heat extremes (events that occurred once per decade pre-industrial) | 4.1 times per decade | 5.6 times per decade |
| Intensity of heat extremes | 1.9 degrees Celsius hotter | 2.6 degrees Celsius hotter |
| Cold extremes | Less frequent but not eliminated | Significantly reduced but extreme cold snaps persist |
| Precipitation extremes | 10.5% wetter | 14% wetter |
India-Specific Projections
| Impact | Projection |
|---|---|
| Heat wave frequency | 3--4 times more frequent by 2100 under RCP 8.5 scenario |
| Heat wave duration | Average duration increasing by 12--18 days per event |
| Agricultural losses | Wheat yield decline of 6--23% per degree Celsius increase in temperature |
| Water stress | Increased evapotranspiration reducing water availability in already stressed basins |
| Urban heat | Indian cities projected to experience 15--25 additional extreme heat days per year by 2050 |
Adaptation Strategies
Structural Measures
| Strategy | Detail |
|---|---|
| Cool roofs | Reflective coatings (white/lime wash, reflective paint) on rooftops reduce indoor temperatures by 2--5 degrees Celsius; promoted under PMAY and Smart Cities Mission |
| Green cover | Urban tree planting, green corridors, rooftop gardens reduce ambient temperatures; mandate in city master plans |
| Water bodies | Restoration of urban lakes, ponds, and wetlands for evaporative cooling |
| Building design | Climate-responsive architecture — passive cooling, cross-ventilation, insulation; updated NBC (National Building Code) guidelines |
| Lightning arresters | Installation of lightning protection systems on buildings, schools, and public spaces in vulnerable areas |
Non-Structural Measures
| Strategy | Detail |
|---|---|
| Early warning systems | IMD colour-coded alerts; mobile-based warnings; community sirens; collaboration with IIITM Pune for forecast models |
| MGNREGA scheduling | Adjusting work hours under MGNREGA to avoid peak heat (12 noon to 3 PM); providing shade and drinking water at worksites |
| Shelter homes | Night shelters (rain baseras) for homeless populations in cold-wave-prone cities; cooling shelters in heat-wave zones |
| Public awareness | Dos and don'ts during heat/cold waves disseminated via media, schools, and Anganwadi centres |
| Crop insurance | PMFBY coverage for weather-related crop losses including hailstorms and unseasonal rain |
| Occupational safety | Guidelines for outdoor workers — mandatory water breaks, rest periods, heat-illness training for supervisors |
Summary Table — Weather Extremes at a Glance
| Hazard | IMD Threshold / Indicator | Peak Season | Primary Region | Key Death Toll Data | Key Response Mechanism |
|---|---|---|---|---|---|
| Heat Wave | Plains >= 40 degrees Celsius + departure >= 4.5 degrees Celsius | March--June | Rajasthan, MP, UP, Telangana, Odisha | 2,500+ deaths in 2015 alone | Heat Action Plans (Ahmedabad model) |
| Severe Heat Wave | Actual >= 47 degrees Celsius OR departure > 6.4 degrees Celsius | April--June | Core heat belt | Cumulative: 11,000+ (2010--2023) | NDMA 2016 Guidelines |
| Cold Wave | Plains min <= 10 degrees Celsius + departure <= -4.5 degrees Celsius | November--February | North India, Bihar | Hundreds annually (homeless, elderly) | Night shelters, fog warning |
| Lightning | Not IMD-threshold based; detected by ENTLN | June--September (monsoon) | MP, Maharashtra, Odisha, Jharkhand | 2,000--2,500+/year | LRIC campaign, mobile alerts |
| Nor'westers | Severe thunderstorm warning | March--May | Bengal, Assam, Bihar | Variable; crop/infrastructure damage | Nowcasting, Doppler radar |
| Hailstorms | Localised warning | Pre/post-monsoon | NW and central India | Primarily crop losses | PMFBY, early warning |
UPSC Relevance
Prelims Focus Areas
- IMD heat wave criteria: plains >= 40 degrees Celsius, departure >= 4.5 degrees Celsius; severe >= 47 degrees Celsius or departure > 6.4 degrees Celsius
- IMD cold wave criteria: plains minimum <= 10 degrees Celsius, departure <= -4.5 degrees Celsius
- Ahmedabad HAP — 2013, first in South Asia
- NDMA heat wave guidelines — 2016
- Lightning deaths: ~2,000--2,500 per year; largest natural hazard killer
- Lightning Resilient India Campaign — launched 2019 by CROPC
- Wet-bulb temperature: 35 degrees Celsius theoretical human survivability limit
- Nor'westers (Kal Baisakhi): pre-monsoon thunderstorms in Bengal/Assam
Mains Focus Areas
- How is climate change altering the frequency and intensity of heat waves in India? What adaptation measures are needed?
- Evaluate the Ahmedabad Heat Action Plan as a model for urban disaster preparedness
- Lightning kills more Indians than any other natural hazard — yet it receives inadequate policy attention. Discuss
- Assess India's preparedness for weather extremes in the context of climate change projections
- Should heat waves be notified as natural disasters under the SDMA framework? Discuss implications
Vocabulary
Heat Wave
- Pronunciation: /hiːt weɪv/
- Definition: A prolonged period of abnormally high temperatures — in India, defined by IMD as maximum temperature reaching at least 40 degrees Celsius in the plains (37 degrees Celsius for coastal areas, 30 degrees Celsius for hills) with a departure of 4.5 degrees Celsius or more above normal for at least two consecutive days over at least two stations in a meteorological sub-division.
- Origin: Compound of Old English hǣtu ("heat") and wafian ("to wave, fluctuate"); first used in meteorological context in the mid-19th century.
Wet-Bulb Temperature
- Pronunciation: /wɛt bʌlb ˈtɛm.prə.tʃər/
- Definition: The temperature measured by a thermometer wrapped in a water-soaked cloth over which air is passed, reflecting the combined effect of heat and humidity — it represents the lowest temperature achievable through evaporative cooling and is the key metric for assessing whether environmental conditions exceed the human body's ability to cool itself through sweating.
- Origin: Technical meteorological term coined in the 19th century; "wet bulb" refers to the wet muslin cloth wrapped around the thermometer's bulb.
Urban Heat Island
- Pronunciation: /ˈɜːr.bən hiːt ˈaɪ.lənd/
- Definition: A metropolitan area that is significantly warmer (typically 2--8 degrees Celsius) than surrounding rural areas due to human activities and built environment — concrete, asphalt, reduced vegetation, waste heat from vehicles and industry, and dense construction all contribute to elevated temperatures.
- Origin: First described by Luke Howard in the 1810s in his studies of London's climate; the term became standard in urban climatology by the mid-20th century.
Key Terms
Heat Action Plan
- Pronunciation: /hiːt ˈæk.ʃən plæn/
- Definition: A comprehensive, city- or state-level preparedness framework that outlines early warning protocols, inter-agency coordination mechanisms, public awareness campaigns, healthcare preparedness measures, and identification of vulnerable populations to reduce mortality and morbidity during heat waves.
- Context: Ahmedabad launched India's (and South Asia's) first HAP in 2013 after a deadly 2010 heat wave; NDMA issued national guidelines in 2016; over 130 Indian cities now have HAPs.
- UPSC Relevance: GS3 (Disaster Management). Prelims: Ahmedabad HAP (2013, first in South Asia), NDMA guidelines (2016). Mains: frequently asked in the context of urban disaster preparedness, climate adaptation, and governance — the Ahmedabad model is an ideal case study combining early warning, institutional coordination, and measurable outcomes.
Lightning Resilient India Campaign
- Pronunciation: /ˈlaɪt.nɪŋ rɪˈzɪl.i.ənt ˈɪn.di.ə kæmˈpeɪn/
- Definition: A national campaign launched on 26 March 2019 by the Climate Resilient Observing Systems Promotion Council (CROPC) with the goal of reducing lightning deaths in India by 80% within three years, using early warning systems, lightning detection networks (including ENTLN), mobile alerts, community awareness programmes, and installation of lightning protection devices.
- Context: Lightning kills 2,000--2,500+ Indians annually — more than any other natural hazard; the campaign achieved over 60% reduction in pilot states within two years.
- UPSC Relevance: GS3 (Disaster Management). Prelims: LRIC launch date (2019), CROPC, and the goal (80% reduction). Mains: useful for answers on underreported disasters, technology in disaster risk reduction, and community-based preparedness.
Sources: IMD — Heat Wave FAQ and Cold Wave FAQ (internal.imd.gov.in), NDMA — National Guidelines for Heat Wave Management (2016), IPCC AR6 (2021--2023), PMC/NIH — Ahmedabad Heat Action Plan study (2014), NCRB — Accidental Deaths and Suicides Report (2022), CROPC — Lightning Resilient India Campaign, Penn State University — Wet-bulb temperature study (2022)
