Discuss the multifaceted effects of droughts while emphasizing the distinctions between aridity and drought. (Answer in 150 words)
Answer: The Earth is surrounded by a thin layer of air called the atmosphere. The air in the atmosphere moves in response to differences in temperature at the equator (warm) and the poles (cold). This movement of air is called global atmospheric circulation. The movement of air across the planet occRead more
Answer: The Earth is surrounded by a thin layer of air called the atmosphere. The air in the atmosphere moves in response to differences in temperature at the equator (warm) and the poles (cold). This movement of air is called global atmospheric circulation. The movement of air across the planet occurs in a specific pattern that is dependent on:
- Latitudinal variation of atmospheric heating.
- The emergence of pressure belts.
- The migration of belts following the apparent path of the sun.
- The distribution of continents and oceans.
- The rotation of the Earth.
The whole system is driven by the equator, which is the hottest part of the Earth. Air rises at the equator, leading to the creation of low pressure and rainfall. When the air reaches the edge of the troposphere (tropopause), it cannot go any further and so it travels to the north and south. The air becomes colder and denser, and falls, creating high pressure and dry conditions at around 30° north and south of the equator. Large cells of air are created in this way. The following are the 3 major cells:
- The Hadley Cell: This is driven by warm rising air. The Coriolis effect causes the air that has risen at the equator and moving to the poles to deflect and become increasingly westerly high up in the atmosphere that the circulation breaks down and the air sinks back towards the ground in the subtropics (30° the ‘horse latitudes’). Once the air has descended back to the ground, it returns to the equator and is deflected to the east – they are known as the easterly trade winds.
- Polar Cell: The same thing happens in the polar regions, but it is driven by sinking cold air. The sinking, cold air at the poles moves back towards the equator, but because it is slow-moving, it becomes increasingly easterly as the underlying earth moves faster, and the circulation eventually breaks down at around 70° latitude. The air then rises again and returns to the poles, resulting in another atmospheric cell.
Ferrel Cell: This lies in between the Polar and Hadley cells, and is a little more complicated. Put simply, it is the net effect of air motions from all the storms or ‘depressions’ that occur in the mid-latitudes. Air sinks in the sub-tropics and rises around 60-70°. In this region, westerly surface winds occur. These cells drive airflow, atmospheric pressure, and rainfall. The rising and sinking of air cause high and low pressure at the surface, respectively. The large-scale winds of the atmosphere initiate large and slow-moving currents of the ocean. Oceans in turn provide input of energy and water vapour into the air. These interactions take place rather slowly over a large part of the ocean.
Jet streams play a significant role in altering the global and regional climate.
(i) The Mediterranean climatic regions are found in the western parts of the continents within the latitudinal zone of 30°-45° in both hemispheres. The Sub-Tropical High-Pressure Belts extending between 30°-35° latitudes are characterized by dry trade winds during the summer season and anti-cyclonic conditions. This belt extends up to 40° latitudes in the Northern hemisphere at the time of summer solstice and in the Southern hemisphere at the time of winter solstice. Thus, the western parts of the continents within the zone of 30°-40° latitudes do not receive rainfall during the summer season. On the other hand, the Sub-Tropical Belt shifts towards the Equator at the time of winter solstice in the Northern hemisphere and at the time of summer solstice in the Southern hemisphere. Consequently, the zone is characterized by the Westerlies, which lead to precipitation during the winter season. The Mediterranean type of climate is thus characterized by dry summers and wet winters. (ii) The regions lying between 60°-70° latitudes are characterized by two types of winds in a year. With the northward migration of the sun at the time of summer solstice, the Polar Easterlies are weakened because the Westerlies extend over these areas due to the northward shifting of Sub-Polar Low-Pressure Belts. The situation is reversed at the time of winter solstice when there is southward migration of the sun. The Polar Easterlies are re-established between 60°-70°N because of the shifting of the belt of the Westerlies southward. Consequently, it creates a climate characterized by wet summers through the Westerlies and associated cyclones and dry winters due to Polar Easterlies. (iii) Monsoon climate is also the result of the shifting of pressure and wind belts. Due to the northward migration of the sun in the Northern hemisphere at the time of summer solstice, the North Inter-Tropical Convergence Zone (NITCZ) is extended up to 30°N latitude over the Indian subcontinent, Southeast Asia, and parts of Africa. Thus, the Equatorial Westerlies are also extended over the aforesaid regions, which become the southwest or summer monsoons. These southwest monsoon winds bring much rain because they come from over the ocean and are associated with tropical cyclones. The NITCZ is withdrawn from the Indian subcontinent and Southeast Asia because of the southward shifting of pressure and wind belts due to the southward migration of the sun at the time of winter solstice. Thus, north-east trades are re-established which leads to the north-east or winter monsoons. Since they come from over the lands, they are dry.
According to the Aridity Anomaly Outlook Index for July, issued by the India Meteorological Department (IMD) this year, at least 85% of districts faced arid conditions across India. Also, around 21.06 percent of India was facing drought-like conditions, according to the Drought Early Warning System.Read more
According to the Aridity Anomaly Outlook Index for July, issued by the India Meteorological Department (IMD) this year, at least 85% of districts faced arid conditions across India. Also, around 21.06 percent of India was facing drought-like conditions, according to the Drought Early Warning System. Aridity is defined, in meteorology and climatology, as the degree to which a climate lacks effective, life-promoting moisture. Drought is a period of abnormally dry weather sufficiently long enough to cause a serious hydrological imbalance.
The differences between the two include:
Multi-dimensional impacts of droughts are the following:
- Water supply: During droughts, communities may have limited access to water for household use, including drinking, cooking, cleaning, etc. Further, it affects transportation and power generation.
- Agriculture: Droughts affect livestock and crops thereby having a devastating effect on farming and food production, which contributes to food price instability. In countries already facing food insecurity, cost spikes can lead to social unrest, migration, and famine.
- Energy: Droughts can raise concerns about the reliability of electricity production from plants that require cooling water to maintain safe operations. Hydroelectric power may also become unavailable during droughts. Further, when heat waves coincide with droughts, electricity demands can grow, compounding stress on the grid.
- Public health: Reduced flows in rivers and streams due to droughts can lead to a concentration of pollutants, thereby threatening the quality of water used for drinking and recreation. Also, drought-fuelled wildfires can expose nearby communities to smoke and pollutants, which can exacerbate chronic respiratory illnesses.
- Social impacts: Due to frequent droughts, there can be outmigration of the population from drought-affected areas leading to greater indebtedness, alienation from land and livestock assets, malnutrition, starvation, etc. There needs to be regular monitoring of droughts in states by setting up Drought Monitoring Centres (DMCs), which will be staffed by a multi-disciplinary team of meteorologists, hydrologists, and agriculture scientists. Also, state governments and businesses need to identify their vulnerability to droughts and improve resilience by practicing and promoting water conservation and enhancing water efficiency.
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