Increased Frequency and Severity of Heat Waves

Urban Heat Island (UHI), Marine Heat Waves (MHW), and Wildfires are three interrelated environmental phenomena that have garnered increasing attention in recent years due to their profound impacts on ecosystems, human health, and socio-economic systems. UHI refers to the elevated temperatures observed in urban areas compared to their rural surroundings, primarily caused by human activities such as transportation, industrial processes, and urbanization. MHWs, on the other hand, are periods of anomalously warm ocean temperatures that persist for days to months, disrupting marine ecosystems and posing risks to coastal communities. Wildfires, driven by a combination of natural factors and human activities, are becoming more frequent and intense, posing significant threats to biodiversity, air quality, and infrastructure. Understanding the complexities and interactions among these phenomena is crucial for devising effective mitigation and adaptation strategies in the face of climate change and urbanization.

URBAN HEAT ISLAND

The urban heat island is characterized as a local and transient phenomenon where specific areas within a city encounter elevated heat loads compared to their surroundings.
This increase in temperature is primarily attributed to the construction of buildings and houses in urban areas, predominantly composed of concrete, which traps and hinders the easy dissipation of heat.
The urban heat island effect is essentially caused by the entrapment of heat between concrete structures, leading to temperature variations ranging from 3 to 5 degrees Celsius.

WHY ARE CITIES HOTTER THAN RURAL AREAS

Observations indicate that areas with more greenery tend to have lower temperatures compared to those with less vegetation.
The presence of green vegetation, including plants, trees, and forests, plays a crucial role in mitigating the occurrence of urban heat islands.
Rural areas enjoy a higher abundance of green cover, including plantations, farmlands, forests, and trees, compared to their urban counterparts.
Transpiration, the process through which plants release water vapor, is a key mechanism that helps regulate temperature.
In urban areas, the frequent construction of high-rise structures, roads, parking spaces, pavements, and public transportation lines contributes significantly to the prevalence of urban heat islands.
The phenomenon is exacerbated by the use of black or dark-colored materials.
Buildings in cities are commonly constructed with materials such as glass, bricks, cement, and concrete, all of which are dark-colored and tend to absorb and retain more heat.

CAUSES OF UHI

The surge in construction activities, ranging from basic urban dwellings to intricate infrastructures, necessitates the use of carbon-absorbing materials like asphalt and concrete for urban expansion.
These materials trap substantial heat, leading to elevated mean surface temperatures in urban areas.
The prevalence of dark surfaces on many urban buildings contributes to reduced albedo, increasing the absorption of heat in the surroundings.
The reliance on air conditioning in buildings with dark surfaces exacerbates the issue.
These surfaces heat up rapidly, demanding more cooling from air conditioners, which, in turn, requires increased energy from power plants, leading to heightened pollution.
Additionally, air conditioners exchange heat with the atmosphere, further contributing to local heating. This creates a cascade effect, amplifying the impact of urban heat islands.
Urban architecture, characterized by tall buildings and narrow streets, obstructs air circulation, diminishes wind speed, and hinders natural cooling effects, a phenomenon known as the Urban Canyon Effect.
The transportation systems, coupled with the widespread use of fossil fuels, also introduce warmth to urban areas.
The scarcity of trees and green spaces impedes evapotranspiration, shade provision, and the removal of carbon dioxide—essential processes for cooling the surrounding air.

HOW CAN UHI BE REDUCED

The increase in construction activities, spanning from simple urban dwellings to complex infrastructures, mandates the utilization of carbon-absorbing materials such as asphalt and concrete for urban expansion.
These materials trap significant heat, resulting in elevated mean surface temperatures in urban areas.
The prevalence of dark surfaces on numerous urban buildings contributes to reduced albedo, amplifying the absorption of heat in the surroundings.
The dependence on air conditioning in buildings with dark surfaces exacerbates the problem.
These surfaces heat up quickly, necessitating more cooling from air conditioners, which, in turn, demands increased energy from power plants, leading to heightened pollution.
Moreover, air conditioners exchange heat with the atmosphere, further contributing to local heating. This sets off a cascade effect, intensifying the impact of urban heat islands.
Urban architecture, characterized by tall buildings and narrow streets, obstructs air circulation, reduces wind speed, and disrupts natural cooling effects, a phenomenon referred to as the Urban Canyon

MARINE HEAT WAVES

Marine Heatwaves (MHWs) are characterized by extended durations of abnormally high Sea Surface Temperature (SST).
These occurrences are associated with detrimental impacts such as coral bleaching, seagrass degradation, and the depletion of kelp forests, posing adverse effects on the fisheries sector.
The primary drivers of marine heatwaves often include ocean currents, which accumulate pockets of warm water, and air-sea heat flux, signifying the exchange of heat between the ocean surface and the atmosphere.
Additionally, winds play a role in either intensifying or mitigating the warming observed during a marine heatwave.
Climate modes, such as El Niño, can influence the likelihood of these events transpiring in specific regions.

IMPACT OF MARINE HEAT WAVES

The marine heatwave in the Bay of Bengal led to increased sea surface temperatures, resulting in higher evaporation rates and a greater moisture supply in the atmosphere.
This surplus of moisture contributed to above-average rainfall in northwest India.
The marine heatwave likely influenced the formation and behavior of depressions in the Bay of Bengal, impacting the frequency and intensity of depressions, particularly on faster timescales (3-10 days).
Depressions, crucial for the monsoon and rainfall patterns, shifted more towards northwest India, causing concentrated rainfall in the region, leading to above-average rainfall.

Other Impacts of Marine Heatwaves:

Affect Ecosystem Structure: Marine heatwaves influence ecosystem structure by supporting certain species while suppressing others. They are linked to mass mortality of marine invertebrates, forcing species to alter behavior and putting wildlife at increased risk.
Change Habitat Ranges of Species: Marine heatwaves can alter habitat ranges, leading to shifts in ecosystems. For instance, the spiny sea urchin off southeastern Australia has expanded southward into Tasmania, affecting kelp forests it feeds upon.
Economic Losses: Impact on fisheries and aquaculture can result in economic losses due to marine heatwaves.
Biodiversity Impact: Biodiversity is significantly affected, with instances of coral bleaching and mass mortality of marine species, such as observed in the Gulf of Mannar near the Tamil Nadu coast.
Increased Risk of Deoxygenation and Acidification: Marine heatwaves often occur alongside other stressors like ocean acidification, deoxygenation, and overfishing. This combination damages habitats, increasing the risk of deoxygenation and acidification.

WILDFIRES

Wildfires, also known as forest fires or bushfires, are uncontrolled fires that rapidly spread across vegetation, including forests, grasslands, shrublands, and other natural landscapes.

Causes of Wildfires:

1. Human Causes:

Carelessness: Unattended campfires, negligent discarding of cigarette butts, and human acts of carelessness contribute significantly to wildfire disasters.
Accidents: Unintentional incidents, deliberate acts of arson, burning of debris, and the use of fireworks are substantial human-induced causes of wildfires.

2. Natural Causes:

Lightning: A considerable number of wildfires are triggered by lightning strikes during thunderstorms.
Volcanic Eruption: Hot magma expelled during a volcanic eruption can cause wildfires when it flows into nearby fields or lands.
Temperature: High atmospheric temperatures and dry conditions create favorable environments for wildfires to start.
Climate Change: Gradual increases in surface air temperatures due to climate change, coupled with extreme conditions during events like El Niño, contribute to the increasing trend in wildfires.

Types of Wildfires:

Crown Fires:
- Characteristics: These fires burn trees up their entire length to the top.
- Intensity: Crown fires are the most intense and dangerous wildland fires.
Surface Fires:
- Characteristics: These fires burn only surface litter and duff.
- Intensity: Surface fires are the easiest to put out and cause the least damage to the forest.
Ground Fires:
- Characteristics: Also known as underground or subsurface fires, they occur in deep accumulations of humus, peat, and similar dead vegetation.
- Movement: Ground fires move slowly but can become challenging to fully suppress.
- Persistence: During prolonged drought, these fires can smolder underground throughout winter, emerging at the surface again in spring.

FAQs-URBAN HEAT ISLAND

Q1: What is the Urban Heat Island (UHI) phenomenon?

A1: The Urban Heat Island is a local and temporary occurrence where certain areas within a city experience higher temperatures compared to their surroundings. This is primarily due to the construction of buildings, predominantly made of concrete, trapping and impeding the dissipation of heat.

Q2: Why are cities hotter than rural areas?

A2: Areas with more greenery, such as plants and trees, tend to have lower temperatures. Urban areas, with fewer green spaces and more concrete structures, experience higher temperatures. Factors like construction materials, dark surfaces, reliance on air conditioning, and the scarcity of trees contribute to the urban heat island effect.

Q3: What causes Urban Heat Island?

A3: Urban Heat Island is caused by carbon-absorbing materials like asphalt and concrete used in construction, dark surfaces reducing albedo, air conditioning reliance leading to increased energy consumption, urban architecture hindering air circulation (Urban Canyon Effect), transportation systems, and the lack of trees and green spaces.

Q4: How can Urban Heat Island be reduced?

A4: Reduction strategies include using alternative construction materials, promoting reflective surfaces, encouraging green spaces, adopting energy-efficient cooling methods, implementing sustainable urban planning, and increasing tree cover.

Q5: What are Marine Heatwaves (MHWs)?

A5: Marine Heatwaves are prolonged periods of abnormally high Sea Surface Temperature (SST) with detrimental impacts on marine ecosystems. They are linked to coral bleaching, seagrass destruction, and fisheries sector disruptions.

Q6: How does a Marine Heatwave impact rainfall in specific regions?

A6: A Marine Heatwave can influence sea surface temperatures, leading to higher evaporation rates. This surplus moisture contributes to above-average rainfall in specific regions, as observed in the Bay of Bengal, impacting weather systems like depressions and altering rainfall patterns.

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Increased Frequency and Severity of Heat Waves – Urban Heat Island, Marine Heat Waves, Wildfires – UPSC Environment Notes