Extreme climatic and weather events
Objective: The explanation of climatic phenomena and extreme weather changes aims to enhance scientific understanding of the mechanisms and consequences of these phenomena, in order to improve the prediction and
management of climate-related hazards and to inform the formulation of climate adaptation policies.
Subtopics:
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- Extreme Weather Events
- Heat Waves
- Cold Waves
- Floods
- Droughts
- Dust Storms
- Wildfires
- Famine
Extreme Weather Events
Extreme weather events, classified as meteorological disasters, are temperaturedependent hazards involving significant deviations from normal climatic conditions within a given geographic area. The Intergovernmental Panel on Climate Change (IPCC) predicts increasing frequency and intensity of extreme temperature events with continued global warming.
Such extremes contribute not only to mortality but also to illness, particularly exacerbating health issues such as cardiovascular diseases and mortality across various cities worldwide. These effects are most pronounced among vulnerable populations, including the elderly, children, individuals with cardiovascular, respiratory, or renal diseases, and people with mental health conditions.
Heatwaves
A heatwave is an episode of abnormally high temperature for a given region and time of year. Because average temperature varies by geographical context, what constitutes a heatwave in one area may be normal elsewhere. There is no universally accepted definition of a heatwave, as its intensity, duration, and spatial extent vary widely. Even the World Meteorological Organization (WMO) lacks a standard global definition.
The WMO generally defines a heatwave as a period of five or more consecutive days during which the daily maximum temperature exceeds the longterm average maximum by 5°C (9°F) or more. National definitions differ: for instance, the Indian Meteorological Department considers temperatures 5–6°C or higher than normal as a heatwave, whereas the U.S. National Weather Service defines it as “a prolonged period of unusually hot and often humid weather lasting at least two days.”
Research consistently demonstrates the health impacts of heatwaves, including increased hospital admissions for cardiovascular and respiratory illnesses, higher mortality rates, greater fire hazards, elevated demand for emergency services, and substantial economic burdens on healthcare systems.
Cold Waves
A cold wave refers to an extended period of abnormally cold conditions, marked by temperatures significantly below regional averages. According to the U.S. National Weather Service, it involves a rapid temperature decline within 24 hours to levels requiring protective measures in agriculture, industry, commerce, and social activities. Thus, two main parameters define cold waves: the rate of temperature decline and the minimum temperature achieved, both of which vary by region and season.
Thresholds defining the onset of cold waves vary across countries and within regions; for example, temperatures below the 10th, 5th, or even 1st percentile sustained over 5–10 consecutive days may signify a cold wave. Their effects parallel those of heatwaves, contributing to elevated hospital admissions and mortality from cardiorespiratory illnessesparticularly among children, the elderly, and other vulnerable groupsand causing hypothermia and increased emergency healthcare demands.
Dust and Sandstorms
Dust and sandstorms occur in arid and semiarid regions when strong winds lift fine particles into the atmosphere, reducing visibility. Different organizations and researchers define these storms by visibility thresholds or particulate matter (PM₁₀) concentrations. During such events, levels of heavy metals and other elements in the air rise, exposing humans to additional pollutants beyond dust particles. These particles, typically 0.1–10 micrometers in size, can penetrate the respiratory system and harm health. The WHO attributes millions of premature deaths annually to particulate matter exposure, with studies linking dust storms to higher rates of cardiovascular, respiratory, and cerebrovascular diseases. Climate change, through increased droughts and heat waves, is expected to intensify both the frequency of dust storms and the concentration of related pollutants in the future.
Floods
Floods result from heavy rainfall, snowmelt, rising water levels, dam or glacier failures, or reduced soil infiltration. Human activitiessuch as deforestation, unsafe construction in flood-prone areas, and climate changehave increased both the frequency of floods and community vulnerability. Floods are classified into gradual floods, developing slowly from sustained rainfall, and flash floods, caused by sudden water surges that often lead to severe damage and casualties. Their health impacts range from immediate effects, such as drowning and injuries, to medium-term issues like water contamination, infectious and respiratory diseases, and long-term consequences, including disabilities, mental health problems, and wider social and public health challenges.
Drought
Drought and associated dust storms occur in dry regions when strong winds suspend fine particles in the atmosphere, reducing visibility. Definitions of dust storms vary by organization and researcher, often based on visibility thresholds or PM₁₀ concentrations. During these events, atmospheric levels of heavy metals and other elements increase, posing significant health risks as people are exposed to both dust and toxic pollutants. The fine particles, mainly 0.1–10 micrometers, can reach deep into the respiratory system and cause harmful effects. The WHO reports over four million premature deaths annually due to exposure to airborne particulate matter, while studies link dust storms to heightened rates of cardiovascular, respiratory, and neurological diseases. Climate change factors such as droughts, higher temperatures, and heat waves are expected to raise both the frequency of dust storms and pollutant concentrations in the future.
Forest Fires
Wildfires are among the primary drivers of forest degradation worldwide, destroying hundreds of thousands of hectares of vegetationincluding trees, shrubs, and grasseseach year. Recent changes in social and climatic conditions have markedly influenced global forest fire regimes, resulting in more severe damage than in the past. Human activity has also significantly contributed to changes in wildfire frequency, particularly in both global and Iranian forests, although the spatial extent of fires remains more highly correlated with natural conditions favorable to fire persistence, vegetation type, and climate.
Wildfires are common phenomena, with hundreds occurring annually worldwide. They may be referred to as forest fires, wildland fires, grassland fires, bushfires, or mountain fires. While these fires typically originate in wildland regions, they can also destroy residential areas and agricultural lands. During summer and drought periods, dried vegetation, leaves, and fallen branches can easily ignite under heat and oxygen flow. Causes include lightning, human negligence, arson, volcanic eruptions, heat waves, and drought.
Famine
The United Nations officially declares a famine in a region when three critical conditions are met: (1) at least 20% of households face extreme food shortages with fewer than 2,100 kilocalories available per person per day; (2) more than 30% of children suffer from acute malnutrition; and (3) the daily death rate exceeds 2 deaths per 10,000 people or 4 deaths per 10,000 children. The UN’s Integrated Food Security Phase Classification (IPC) defines famine as Phase 5, the most severe level of food insecurity.
