Geography

Table of content

• Weathering
• Mass Wasting
• Erosion and Deposition
• Soil Formation
• Landscape (Geological) Cycles
• Davis Cycle
• Penck Cycle

Weathering

Weathering is the general term applied to the combined action of all processes that cause rock to disintegrate physically and decompose chemically because of ex- posure near the Earth’s surface through the elements of weather. Among these elements temperature, rainfall, frost, fog and ice are the important ones. Weathering begins as soon as rocks come in contact with one or more than one elements of weather on the surface of the earth. In nature, generally both the disintegration and decomposition act together at the sametime and assist each other. We must remember that the weathered material (i.e. disintegrated and decomposed) lie in situ (i.e. at its original position). In this process no transportation or movement of material is involved other than its falling down under the force of gravity.

Weathering is the response of rocks to a changing environment. For example, plutonic rocks form under conditions at high pressures and temperatures. At the Earth’s surface they are not as stable as the conditions under which they formed. In response to the environmental change, they gradually weather (transform to more stable minerals).

Different types of Weathering are:-

1. Physical Weathering :-The mechanical breakup or disintegration of rock doesn’t change mineral makeup. It creates broken fragments or “detritus.” which are classified by size:

• Coarse-grained – Boulders, Cobbles, and Pebbles.
• Medium-grained – Sand
• Fine-grained – Silt and clay (mud).

Various process of Physical weathering are:-

• Development of Joints – Joints are regularly spaced fractures or cracks in rocks that show no offset across the fracture (fractures that show an offset are called faults).
• Crystal Growth – As water percolates through fractures and pore spaces it may contain ions that precipitate to form crystals. As these crystals grow they may exert an outward force that can expand or weaken rocks.
• Thermal Expansion – Although daily heating and cooling of rocks do not seem to have an effect, sudden exposure to high temperature, such as in a forest or grass fire may cause expansion and eventual breakage of rock. Campfire example.
• Root Wedging – Plant roots can extend into fractures and grow, causing expansion of the fracture. Growth of plants can break rock – look at the sidewalks of New Orleans for example.
• Animal Activity – Animals burrowing or moving through cracks can break rock.
• Frost Wedging – Upon freezing, there is an increase in the volume of the water (that’s why we use antifreeze in auto engines or why the pipes break in New Orleans during the rare freeze). As the water freezes it expands and
  exerts a force on its surroundings. Frost wedging is more prevalent at high altitudes where there may be many freeze-thaw cycles.

2. Chemcial weathering :-involves a chemical transformation of rock into one or more new compounds.  A group of weathering processes viz; solution , carnonation, hydration , oxidation and reduction acts on the roks to decompose, dissolve orreduce them to a fine clastic state through chemical reactions by oxygen ,surface /soil water and other acids. Water and air along with heat must be present to speed up all chemical reactions. Over and above the carbon dioxide present in the air, decomposition of plants and animals increases the quanitity of carbon dioxide underground . Chamical weathering involves four major processes:

• Oxidation is the process in which atmospheric oxygen reacts with the rock to produce oxides. The process is called oxidation. Greatest impact of this process is observed on ferrous minerals. Oxygen present in humid air reacts with iron grains in the rocks to form a yellow or red oxide of iron. This is called rusting of the iron. Rust decomposes rocks completely with passage of time.
• Carbonation is the process by which various types of carbonates are formed. Some of these carbonates are soluble in water. For example, when rain water con- taining carbon dioxide passes through pervious limestone rocks, the rock joints enlarge due to the action of carbonic acid. The joints enlarge in size and lime is removed in solution. This type of breakdown of rocks is called carbonation.
• Hydration is the process by which water is absorbed by the minerals of the rock. Due to the absorption of water by the rock, its volume increases and the grains lose their shape. Feldspar, for example, is changed into kaolin through hydration. Kaolin on Vindhyan Hills near Jabalpur has been formed in this manner.
• Solution is the process in which some of the minerals get dissolved in water. They are therefore removed in solution. Rock salt and gypsum are removed by this process.

3. Biotic weathering :- is a type of weathering that is caused by living organisms. Most often the culprit ofbiotic weathering are plant roots. These roots can extend downward, deep into rock cracks in search of water, and nutrients. In the process they act as a wedge, widening and extending the cracks.

Mass Wasting

Mass wasting is defined as the down slope movement of rock and regolith near the Earth’s surface mainly due to the force of gravity.   Mass movements are an important part of the erosional process, as it moves material from higher elevations to lower elevations where transporting agents like streams and glaciers can then pick up the material and move it to even lower elevations.   Mass movement processes are occurring continuously on all slopes; some act very slowly, others occur very suddenly, often with disastrous results.  Any perceptible down slope movement of rock or regolith is often referred to in general terms as a landslide.  Landslides, however, can be classified in a much more detailed way that reflects the mechanisms responsible for the movement and the velocity at which the movement occurs. Mass wasting can be classified as:-

• Slope Failures – a sudden failure of the slope resulting in transport of debris down hill by sliding, rolling, falling, or slumping.
• Sediment Flows – debris flows down hill mixed with water or air.

Erosion and Deposition

Soil erosion is the deterioration of soil by the physical movement of soil particles from a given site. Wind, water, ice, animals, and the use of tools by man are usually the main causes of soil erosion. It is a natural process which usually does not cause any major problems. It becomes a problem when human activity causes it to occur much faster than under normal conditions.The removal of soil at a greater rate than its replacement by natural agencies (water, wind etc.) is known as soil erosion.
Soil erosion is of four types which are as follows:-

• Wind Erosion :-Winds carry away vast quantity of fine soil particles and sand from deserts and spread it over adjoining cultivated land and thus destroy their fertility. This type of erosion is known as wind erosion. It takes place in and around all desert regions of the world. In India, over one lakh kilometers of land is under Thar Desert, spread over parts of Gujarat, Haryana, Punjab and Rajasthan states. These areas are subject to intense wind erosion.
• Sheet Erosion :-Water when moves as a sheet takes away thin layers of soil. This type of erosion is called sheet erosion. Such type of erosion is most common along the river beds and areas affected by floods. In the long run, the soil is com- pletely exhausted due to removal of top soil and becomes infertile.
• Rill Erosion :-The removal of surface material usually soil, by the action of running water. The processes create numerous tiny channels (rills) a few centimeters in depth, most of which carry water only during storms.
• Gully Erosion :-When water moves as a channel down the slope, it scoops out the soil and forms gullies which gradually multiply and in the long run spread over a wide area. This type of erosion is called gully erosion. The land thus dissected is called bad lands or ravines. In our country, the two rivers Chambal and Yamuna are famous for their ravines in U.P. and M.P. states.

Deposition / Sedimentation – occurs when sediment settles out as winds/water current die down, or as glaciers melt. When sediment is transported and deposited, it leaves clues to the mode of transport and deposition. For example, if the mode of transport is by sliding down a slope, the deposits that result are generally chaotic in nature, and show a wide variety of particle sizes. Grain size and the interrelationship between grains gives the resulting sediment texture. Thus, we can use the texture of the resulting deposits to give us clues to the mode of transport and deposition. Sorting – The degree of uniformity of grain size. Particles become sorted on the basis of density, because of the energy of the transporting medium. High energy currents can carry larger fragments. As the energy decreases, heavier particles are deposited and lighter fragments continue to be transported. This results in sorting due to density.

Soil Formation

Soil consists of rock and sediment that has been modified by physical and chemical interaction with organic material and rainwater, over time, to produce a substrate that can support the growth of plants.Soil is the uppermost layer of the land surface that plants use and depend on for nutrients, water and physical support.

Factors of soil formation are:-

• Parent material: soil formation depends on the mineral material, or organic material from which the soil is formed. Soils will carry the characteristics of its parent material such as color, texture, structure, mineral composition and so on. For example, if soils are formed from an area with large rocks (parent rocks) of red sandstone, the soils will also be red in color and have the same feel as its parent material.
• Time: Soils can take many years to form. Younger soils have some characteristics from their parent material, but as they age, the addition of organic matter, exposure to moisture and other environmental factors may change its features. With time, they settle and are buried deeper below the surface, taking time to transform. Eventually they may change from one soil type to another.
• Climate:Two important climatic components, temperature and precipitation are key. They determine how quickly weathering will be, and what kind of organic materials may be available on and inside of the soils. Moisture determines the chemical and biological reactions that will occur as the soils are formed. Warmer climate with more rainfall means more vegetative cover and more animal action. It also means more runoff, more percolation and more water erosion. They all help to determine the kind of soils in an area.
• Relief:i.e. the landscape position and the slopes it has. Steep, long slopes mean water will run down faster and potentially erode the surfaces of slopes. The effect will be poor soils on the slopes, and richer deposits at the foot of the slopes. Also, slopes may be exposed to more direct sunlight, which may dry out soil moisture and render it less fertile.
• Organisms:The source and richness of organic matter is down to the living things (plants and animals) that live on and in the soils. Plants in particular, provide lots of vegetative residue that are added to soils. Their roots also hold the soils and protect them from wind and water erosion. They shelter the soils from the sun and other environmental conditions, helping the soils to retain the needed moisture for chemical and biological reactions. Fungi, bacteria, insects, earthworms, and burrowing animals help with soil aeration. Worms help breakdown organic matter and aid decomposition. Animal droppings, dead insects and animals result in more decaying organic matter. Microorganisms also help with mineral and nutrient cycling and chemical reactions.

Davis Cycle

After the upliftment of landmass by the tectonic forces the process of denudation is started. The rivers, valleys and associated landforms passes through distinctive stages, provided that there has been no significant interference by earth movements or by changes of sea-level or climate. This idealized concept of landscape evolution was introduced to geomorphology more than sixty years ago by W.M. Davis, who referred to the whole sequence of stage as a Cycle of Erosion.

The basic goal of Davisian model of geographical cycle and general theory of landform development was to provide basis for a systematic descriptions and genetic classification of landforms. According to this concept a landscape has a definite life history, and as the processes of land structure operate on it the surface features are marked by several changes in its life time. Thus, the evolution of landscape passes through a cycle, and cycle follows a definite sequence of development.

The successive stage of developmental sequences can be divided into three parts and may be identified as youth, maturity and old age. Davis presentation of scheme was both vigorous and vivid and his colourful analogy of the human life and landscapes both passing through the stages of youth, maturity and old age caught the imagination of scientific world.

• Youth:The uplift is complete and has stopped. Immediately erosion of the uplifted block sets in. The streams follow initial irregularities available without adjusting to the structure. These are consequent streams. The floors of the valley suffer down cutting while the summits remain almost unaffected. Increased relief heralds the beginning of mature age
• Maturity:At this stage, the vertical erosion slows down and the horizontal action increases. A characteristic feature is the erosion of mountain tops at a faster rate than lowering of the valley floor. The coming closer of lines ‘A’ and ‘B’ indicates emergence of a gentle slope. The subsequent streams gain importance now.
• Old Age:A gentle gradient, accentuated by horizontal action and deposition, reduces the erosion intensity. A thick layer of sediment represents the earlier erosion activity. The landforms get mellowed—lines ‘A’ and ‘B’ run parallel to each other. Relicts of mountains or monad knocks are dotting the water divides and a featureless plain—peneplane is produced.

In order to understand the evolution of a particular landscape it is extremely important to know the stage of development. But the geographical structure and the nature of rocks also exert an important influence on the fashioning of landscapes is a function of structure, process and time (as called as stage by the followers of Davis). These three factors are called as ‘Trio of Davis’.

Structure :means lithological (rock types) and structural characteristics (folding, faulting, joints etc.) of rocks. Time was not only used in temporal context but it was also used as a process itself leading to an inevitable progression of change of landform. Process means the agent of denudation including both, weathering and erosion (running water in the case of geographical cycle).

Process:Implies the factors or agents responsible for weathering and erosion.

Time:Implies the stage at which the cycle is—youth, maturity or old age.

Penck Cycle 

According to German geomorphologist Walther Penck, the characteristics of landforms of a given region are related to the tectonic activity of that region. Contrary to the Davisian concept that “landscape is a function of structure, process and time (stage)”, Penck put forward his view that geomorphic forms are an expression of the phase and rate of uplift in relation to the rate of degradation, where it is assumed that interaction between the two factors, uplift and degradation, is continuous. According to Penck’s view the landforms observed at any given site give expression to the relation between the two factors of uplift and degradation that has been or is in effect, and not to a stage in a progressive sequence.

Penck proposed three types of valley slopes on the basis of erosional intensity acting on crustal movements.

1. Straight slope:Indicating uniform erosion intensity and a uniform development of landforms or ‘Gleichformige Entwickelung’ in German.
2. Convex slope:Indicating waxing erosion intensity and a waxing development of landforms or ‘Aufsteigende Entwickelung.
3. Concave slope:Indicating waning erosion intensity and a waning development of landforms or ‘Absteigende Entwickelung.’

Different Phases according to Penck are:-

(a) Phase of waxing rate of landform development (Aufsteigende Entwickelung)
Endogenetic forces cause the slow rise of the initial land surface (Primarumpf) but later on the upliftment is rapid.
In this phase, because of upliftment and the increase in the channel gradient and stream velocity rivers continue to degrade their valleys with accelerated rate of valley deepening.
The rate of upliftment is faster than the rate of down-cutting. It results in the formation of gorges and narrow V-shaped valleys. Since the upliftment of landmass far exceeds the valley deepening, the absolute height goes on increasing.
Altitude of the summit of interfluves and valley bottom continues to increase due to the faster rate of upliftment than that of the vertical erosion.
This phase is characterized by the maximum altitude and the maximum relief (relative heights of the valley floors).

(b) Phase of uniform development of land form (Gleichformige Entwickelung)
This phase may be divided into three sub-phases on the basis of upliftment and consequent degradation

(i) The first sub-phase is characterised by the continuance of accelerated rate of uplift. The absolute height continues to increase because the rate of upliftment is still greater than the rate of down-cutting.
The maximum altitude or the absolute relief is achieved, but relative relief remains unaffected because the rate of valley deepening is almost equal to the rate of lowering of the summits of stream interfluves.
The valley walls are steep. This is known as the phase of uniform development because of uniformity in the rate of valley deepening and lowering of divide summits.
(ii) In the second sub-phase the absolute relief neither increases nor decreases. This is due to the fact that rate of upliftment and the rate of erosion are the same. However, in this phase the absolute height and the relative relief’s are unchanged. So this may be called the phase of uniform development of landforms.
(iii) In this sub-phase there is no more upliftment of land.

(c) Phase of Wanning development of landscape (Absteigende Entwickelung)
The erosional processes dominate in this phase. The lateral erosion rather than vertical erosion is more important. There is progressive decrease in the height of the landforms. In other words, the absolute and the relative relief decline.
The valley side slope consists of two parts, the upper and the lower. The upper segment continues to have steep angle which is called as gravity slope.
The lower segment of the slope is called wash slope. The wash slope is composed of talus materials of lower inclination which is formed at the base of valley sides.
The later part of this phase is marked by the presence of inselbergs and a series of concave wash slopes.
This type of extensive surface produced at the fag end of absteigende entwickelung has been labelled is endrumpf which may be equivalent to peneplain as envisaged by Davis in his cycle concept. Thus, the cycle of landscape development as envisaged by Penck ends in endrumpf.

The temperature is the measurement in degrees of how hot (or cold) a thing (or a place) is.
The temperature of the atmosphere is not same across the Earth. It varies in spatial and temporal dimensions. The temperature of a place depends largely on the insolation received by that place. The interaction of insolation with the atmosphere and the earth’s surface creates heat which is measured in terms of temperature. It is important to know about the temperature distribution over the surface of the earth to understand the weather, climate, vegetation zones, animal and human life etc. following factors determine the temperature of air at any place.

1. The latitude of the place – Intensity of insolation depends on the latitude. The amount of insolation depends on the inclination of sun rays, which is further depends upon the latitude of the place. At the equator sun’s rays fall directly overhead throughout the year. Away from the equator towards poles, the inclination of the Sun’s rays increases. In conclusion, if other things remain the same, the temperature of air goes on decreasing from the equator towards poles.
2. The altitude of the place – the atmosphere is largely heated indirectly by re-radiated terrestrial radiation from the earth’s surface. Therefore, the lower layers of the atmosphere are comparatively warmer than the upper layers, even in the same latitudes. For example, Ambala (30 21’ N) and Shimla (31 6’) are almost at the same latitude. But the average temperature of shimla is much lower than the Ambala. It is because Ambala is located in plain at an altitude of 272 m above sea level whereas Shimla is located at an altitude of 2202 m above sea level. In other words, the temperature generally decreases with increasing height (figure 6(a)). The rate of decrease of temperature with height is termed as the normal lapse rate. It is 6.5°C per 1,000 m. That’s why, the mountains, even in the equatorial region, have snow covered peaks, like Mt. Kilimanjaro, Africa.
3. Distance from the Sea – the land surface is heated at a faster rate than the water N surface. Thus the temperature of the air over land and water surfaces is not the same Student Notes: at a given time. In summers, the sea water is cooler than the land and in winters, land is much colder than the sea water. The coastal areas experience the sea breezes during the daytime and the land breezes during the night time. This has a moderating influence on the temperature of the coastal areas. Against this the places in the interior, far away from the sea, have extreme climate. The daily range of temperature is less near the coastal area and it increases with increase in distance from the sea coast (figure 6(b)). The low daily range of temperature is the characteristic of marine climate. That’s why, the people of Mumbai have hardly any idea of extremes of temperature.

(a) Horizontal Distribution of Temperature
Distribution of temperature across the latitudes over the surface of the earth is called its horizontal distribution. On maps, the horizontal distribution of temperature is commonly shown by “Isotherms”, lines connecting points that have equal temperatures. An isotherm is made of two words ‘iso’ and ‘therm’, ‘Iso’ means equal and ‘therm’ means” temperature. If you study an isotherm map you will find that the distribution of temperature is uneven. The factors responsible for the uneven distribution of temperature are as follows:
(i) Latitude
(ii) Land and Sea Contrast
(iii) Relief and Altitude
(iv) Ocean Currents
(v) Winds
(vi) Vegetation Cover
(vii) Nature of the soil
(viii) Slope and Aspect

(b) Vertical Distribution of Temperature
The permanent snow on high mountains, even in the tropics, indicate the decrease of temperature with altitute. Observations reveals that there is a fairly regular decrease in temperature with an increase in altitude. The average rate of temperature decrease upward in the troposphere is about 6 C per km, extending to the tropopause. This vertical gradient of temperature is commonly referred to as the standard atmosphere or normal lapse rate, but is varies with height, season, latitude and other factors. Indeed the actual lapse rate of temperature does not always show a decrease with altitude.

Temperature Inversion

Temperature decreases with increase in altitude. In normal conditions, as we go up, temperature decreases with normal lapse rate. It is 6.5°C per 1,000 m. Against this normal rule sometimes, instead of decreasing, temperature may rise with the height gained. The cooler air is nearer the earth and the warmer air is aloft. This rise of temperature with height is known as Temperature inversion. Temperature inversion takes place under certain specific conditions. These are discussed below:

•  Long winter nights – if in winters the sky is clear during long nights, the terrestrial radiation is accelerated. The reason is that the land surface gets cooled fairly quickly. The bottom layer of atmosphere in contact with the ground is also cooled and the upper layer remains relatively warm.
• Cloudless clear sky – The clouds obstruct the terrestrial radiation. But this radiation does not face any obstacles for being reflected into space when the sky is clear. Therefore the ground is cooled quickly and so is the air in contact with it cooled.
• Dry air – humid air absorbs the terrestrial radiation but dry air is no obstruction to terrestrial radiation and allows the radiation to escape into space.
• Calm atmosphere – the blowing of winds bring warm and cold air into contact. Under conditions of calm atmosphere the cold air stays put near the ground.
• Ice covered surface – in ice covered areas due to high albedo less insolation is received. During night due to terrestrial radiation most of the heat is lost to atmosphere and the surface is cooled. The air in contact with it is also cooled but the upper layer remains warm.

Earthquakes occur when energy stored in elastically strained rocks is suddenly released. This release of energy causes intense ground shaking in the area near the source of the earthquake and sends waves of elastic energy, called seismic waves, throughout the Earth. Earthquakes can be generated by bomb blasts, volcanic eruptions, sudden volume changes in minerals, and sudden slippage along faults. Earthquakes are definitely a geologic hazard for those living in earthquake prone areas, but the seismic waves generated by earthquakes are invaluable for studying the interior of the Earth.

The point within the earth where the fault rupture starts is called the focus or hypocenter. This is the exact location within the earth were seismic waves are generated by sudden release of stored elastic energy.

The epicenter is the point on the surface of the earth directly above the focus. Sometimes the media get these two terms confused.

Seismic waves are the vibrations from earthquakes that travel through the Earth; they are recorded on instruments called seismographs. Seismographs record a zig-zag trace that shows the varying amplitude of ground oscillations beneath the instrument. Sensitive seismographs, which greatly magnify these ground motions, can detect strong earthquakes from sources anywhere in the world. The time, locations, and magnitude of an earthquake can be determined from the data recorded by seismograph stations.

Two of the most common methods used to measure earthquakes are the Richter scale and the moment magnitude scale.

The Richter scale is used to rate the magnitude of an earthquake, that is the amount of energy released during an earthquake.
The Richter scale doesn’t measure quake damage (which is done by Mercalli Scale) which is dependent on a variety of factors including population at the epicentre, terrain, depth, etc. An earthquake in a densely populated area which results in many deaths and considerable damage may have the same magnitude as a shock in a remote area that does nothing more than frightening the wildlife. Large-magnitude earthquakes that occur beneath the oceans may not even be felt by humans. Richter Scale of Earthquake Energy
The magnitude of an earthquake is determined using information gathered by a seismograph.
The Richter magnitude involves measuring the amplitude (height) of the largest recorded wave at a specific distance from the seismic source. Adjustments are included for the variation in the distance between the various seismographs and the epicentre of the earthquakes.
The Richter scale is a base-10 logarithmic scale, meaning that each order of magnitude is 10 times more intensive than the last one.

Beginning of the Universe started about 13.6 billion years ago,when the Big Bang created the universe from a point source.
During this process, light elements, like H, He, Li, B, and Be formed. From this point in time, the universe began to expand and has been expanding ever since.
Concentrations of gas and dust within the universe eventually became galaxies consisting of millions of stars.
Within the larger stars, nuclear fusion processes eventually created heavier elements, like C, Si, Ca, Mg, K, and Fe.
Stars eventually collapse and explode during an event called a supernova. During a supernova, heavier elements, from Fe to U, are formed. (See figure 1.9 in your text).
Throughout galaxies clusters of gas attracted by gravity start to rotate and accrete to form stars and solar systems. For our solar system this occurred about 4.6 billion years ago.
The ball at the center grows dense and hot, eventually nuclear fusion reactions start and a star is born (in our case, the sun).
Rings of gas and dust orbiting around the sun eventually condenses into small particles. These particles are attracted to one another and larger bodies called planetismals begin to form.
Planetesimals accumulate into a larger mass. An irregularly-shaped proto-Earth develops.
The interior heats and becomes soft. Gravity shapes the Earth into a sphere. The interior differentiates into a nickel-iron core, and a stony (silicate) mantle.
Soon, a small planetoid collides with Earth. Debris forms a ring around the Earth.The debris coalesces and forms the Moon.
The atmosphere develops from volcanic gases. When the Earth becomes cool enough, moisture condenses and accumulates, and the oceans are born.

A tsunami is a very long-wavelength wave of water that is generated by sudden displacement of the seafloor or disruption of any body of standing water. Tsunami are sometimes called “seismic sea waves”, although they can be generated by mechanisms other than earthquakes.
Tsunami have also been called “tidal waves”, but this term should not be used because they are not in any way related to the tides of the Earth. Because tsunami occur suddenly, often without warning, they are extremely dangerous to coastal communities.

Tsunamis can be associated with earthquakes. Sometimes a large earthquake beneath the ocean floor will produce a tsunami, which is a series of large waves.

The rate at which a wave loses its energy is inversely related to its wavelength. Since a tsunami has a very large wavelength, it will lose little energy as it propagates. Thus, in very deep water, a tsunami will travel at high speeds with little loss of energy.

As a tsunami leaves the deep water of the open sea and arrives at the shallow waters near the coast, it undergoes a transformation. Since the velocity of the tsunami is also related to the water depth, as the depth of the water decreases, the velocity of the tsunami decreases. The change of total energy of the tsunami, however, remains constant.

Furthermore, the period of the wave remains the same, and thus more water is forced between the wave crests causing the height of the wave to increase. Because of this “shoaling” effect, a tsunami that was imperceptible in deep water may grow to have wave heights of several meters or more.

The main damage from tsunami comes from the destructive nature of the waves themselves. Secondary effects include the debris acting as projectiles which then run into other objects, erosion that can undermine the foundations of structures built along coastlines, and fires that result from disruption of gas and electrical lines. Tertiary effects include loss of crops and water and electrical systems which can lead to famine and disease.

Climatic Regions of India : Trewartha’s Classification