Geographical Terms : Daily Current Affairs

Geographical Terms


  • Acid rain refers to a mixture of deposited material, both wet and dry, coming from the atmosphere containing more than normal amounts of nitric and sulfuric acids. Simply put, it means rain that is acidic in nature due to the presence of certain pollutants in the air due to cars and industrial processes.
  • It is easily defined as rain, fog, sleet or snow that has been made acidic by pollutants in the air as a result of fossil fuel and industrial combustions that mostly emits Nitrogen Oxides (NOx) and Sulfur Dioxide (SO2). Acidity is determined on the basis of the pH level of the water droplets by assigning it a number between 0 and 14, where 0 represents extreme acidity and 14 represents superlative basicity (the opposite of acidity).
  • Acid rain generally leads to weathering of buildings, corrosion of metals, and peeling of paints on surfaces.
  • Erupting volcanoes contains some chemicals that can cause acid rain. Apart from this, the burning of fossil fuels, the running of factories and automobiles due to human activities are a few other reasons behind this activity.
  • Both natural and man-made sources are known to play a role in the formation of acid rain. But, it is mainly caused by the combustion of fossil fuels which results in emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx).
  • Volcanic eruptions, Decaying vegetation, wildfires and biological processes within the environment, lightning strikes etc are natural causes of acid rain
  • The activities like air pollution sources emitting sulfur and nitrogen gases like factories, power generation facilities, and automobiles, etc by human are man-made causes.

Effects of Acid Rain

  • Acid rain either falls directly on aquatic bodies or gets run off the forests, roads and fields to flow into streams, rivers and lakes. Over a period of time, acids get accumulated in the water and lower the overall pH of the water body.
  • Acid rain tendency of altering pH and aluminum concentrations greatly affects pH concentration levels in surface water, thereby affecting fish as well as other aquatic life-forms. At pH levels below 5, most fish eggs cannot hatch. Lower pHs can also kill adult fish.
  • Also, reduces biodiversity
  • It makes trees vulnerable to disease, extreme weather, and insects by destroying their leaves, damaging the bark and arresting their growth. Forest damage due to acid rain is most evident in Eastern Europe – especially Germany, Poland and Switzerland.
  • Acid rain highly impacts on soil chemistry and biology. It means soil microbes and biological activity as well as soil chemical compositions such as soil pH are damaged or reversed due to the effects of acid rain.
  • Acid rain on buildings, especially those constructed with limestone, reacts with the minerals and corrode them away. This leaves the building weak and susceptible to decay. Modern buildings, cars, airplanes, steel bridges and pipes are all affected by acid rain. Irreplaceable damage can be caused to the old heritage buildings.
  • The dry depositions of acid rain, also known as gaseous particulates in the air which in this case are nitrogen oxides and sulfur dioxide, can cause serious health problems when inhaled. Intensified levels of acid depositions in dry form in the air can cause lung and heart problems such as bronchitis and asthma.


  • A water catchment (commonly referred to as a “watershed”) is an area of land where all water flows to a single stream, river, lake or even ocean.
  • Natural boundaries of water catchments can be very small for a single creek or stream or quite large—the Colorado River basin for example.
  • Water catchments are widely recognized as the most effective management unit for the protection of water resources, both water quality and supply
  • A water catchment area is home to a complete water-cycle system.
  • A watershed is the land area that drains to a common body of water, such as a stream, lake, bay, or even the ocean. They provide drinking water, habitats for wildlife, soil to grow our food, and locations for fishing, boating and swimming. We all live in a watershed.
  • Rain that does not soak into the ground becomes runoff and carries soil, pollutants, and other materials from the land into our rivers, lakes and bays. Our everyday activities can affect downstream waters.


  • Drainage pattern a pattern created by stream erosion over time that reveals characteristics of the kind of rocks and geologic structures in a landscape region drained by streams.
  • Drainage pattern is the pattern formed by the streams, rivers, and lakes in a particular drainage basin. They are governed by the topography of the land, whether a particular region is dominated by hard or soft rocks, and the gradient of the land.
  • The pattern of tributaries within a drainage basin depends largely on the type of rock beneath, and on structures within that rock (folds, fractures, faults, etc.).

The main types of drainage patterns:

  • Dendritic patterns, which are by far the most common, develop in areas where the rock (or unconsolidated material) beneath the stream has no particular fabric or structure and can be eroded equally easily in all directions. Examples would be granite, gneiss, volcanic rock, and sedimentary rock that has not been folded. Most areas of British Columbia have dendritic patterns, as do most areas of the prairies and the Canadian Shield.
  • Trellis drainage patterns typically develop where sedimentary rocks have been folded or tilted and then eroded to varying degrees depending on their strength. The Rocky Mountains of B.C. and Alberta are a good example of this, and many of the drainage systems within the Rockies have trellis patterns.
  • Rectangular patterns develop in areas that have very little topography and a system of bedding planes, fractures, or faults that form a rectangular network. Rectangular drainage patterns are rare in Canada.
  • Parallel drainage system is a pattern of rivers caused by steep slopes with some relief. Because of the steep slopes, the streams are swift and straight, with very few tributaries, and all flow in the same direction. Parallel drainage patterns form where there is a pronounced slope to the surface. A parallel pattern also develops in regions of parallel, elongate landforms like outcropping resistant rock bands.
  • Radial drainage system, the streams radiate outwards from a central high point. Volcanoes usually display excellent radial drainage. Other geological features on which radial drainage commonly develops are domes and laccoliths. On these features the drainage may exhibit a combination of radial patterns.
  • The centripetal drainage system is similar to the radial drainage system, with the only exception that radial drainage flows out versus centripetal drainage flows in
  • A deranged drainage system is a drainage system in drainage basins where there is no coherent pattern to the rivers and lakes. It happens in areas where there has been much geological disruption. The classic example is the Canadian Shield. During the last ice age, the topsoil was scraped off, leaving mostly bare rock.
  • Angular drainage patterns form where bedrock joints and faults intersect at more acute angles than rectangular drainage patterns. Angles are both more and less than 90 degrees


  • An ecotone is a zone of junction or a transition area between two biomes (diverse ecosystems).
  • Ecotone is the zone where two communities meet and integrate.
  • For e.g. the mangrove forests represent an ecotone between marine and terrestrial ecosystem.
  • Other examples are grassland (between forest and desert), estuary (between fresh water and salt water) and riverbank or marshland (between dry and wet).

Characteristics of Ecotone

  • It may be narrow (between grassland and forest) or wide (between forest and desert).
  • It has conditions intermediate to the adjacent ecosystems. Hence it is a zone of tension.
  • Usually, the number and the population density of the species of an outgoing community decreases as we move away from the community or ecosystem.
  • A well-developed ecotone contains some organisms which are entirely different from that of the adjoining communities.


  • The movement of air across the planet occurs in a specific pattern. The whole system is driven by the equator, which is the hottest part of the Earth. Air rises at the equator, leading to low pressure and rainfall. When the air reaches the edge of the atmosphere, 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.
  • Air rises again at around 60° north and south and descends again around 90° north and south. The names of the cells are shown in the diagram.
  • Global atmospheric circulation creates winds across the planet and leads to areas of high rainfall, like the tropical rainforests, and areas of dry air, like deserts
  • At the equator, the ground is intensely heated by the sun. This causes the air to rise which creates a low-pressure zone on the Earth's surface. As the air rises, it cools and forms thick cumulonimbus (storm) clouds. The air continues to rise up to the upper atmosphere, and the following then happens:
  • The air separates and starts to move both north and south towards the poles.
  • When it reaches about 30° north and south, the air cools and sinks towards the ground forming the subtropical high-pressure zone.
  • As the air sinks, it becomes warmer and drier. This creates an area of little cloud and low rainfall, where deserts are found.
  • The Hadley cell is then complete. The air completes the cycle and flows back towards the equator as the trade winds.
  • In the northern hemisphere, the winds flow to the right and are called northeast trade winds. In the southern hemisphere the winds flow to the left and are called the southeast trade winds. This is down to the Coriolis force and friction.

Contributions of Hadley Cell

  • The Hadley Cell greatly influences the climate, the structure of wind patterns, and temperature contrast between latitudes.
  • Hadley Cell initiates the process of the transfer of heat from the Earth’s equatorial regions gradually towards the Earth’s polar regions.
  • The Hadley Cell is responsible for the formation of clouds and plentiful rainfall in the Earth’s equatorial regions. This phenomenon is principally responsible for the presence of tropical rainforests in the equatorial regions


  • Old NCERTs class 6-10
  • Biology Discussion
  • Centre for watershed protection
  • BBC
  • NIOS material
  • NASA website