The term refers to the body of water which takes varied forms (liquid, gaseous, solid). Such bodies of water include seas, rivers, clouds, ground water. In simple terms hydrosphere can be defined as the part of the earth which constitutes water.
The hydrological cycle
This is the movement of water between the surface of earth and the atmosphere. The water circulates from the surface of the earth to the atmosphere as well as from the atmosphere to the surface of the earth.
The cycle is composed of the features and processes. The features include sea/lakes, runoffs (rivers/streams), clouds, precipitation (rain, snow, sleet, mist, fog and hail), ground water and vegetation.
On other hand, the processes encompass:
a. Evaporation – the change of form of water from liquid to vapour (steam). This process occurs in seas, lakes, rivers, streams, reservoirs.
b. Condensation – the change of state of water from vapour to liquid. This process occurs in the atmosphere and it leads to formation of clouds followed by precipitation.
c. Infiltration – the sinking of water into the ground. It is also known as soaking. This process results into formation of ground water.
d. Percolation – the movement of ground water from one point to another point.
e. Transpiration – the loss of water from plants (forests/vegetation). This process enables the change of state of water from liquid to vapour.
g. Evapotranspiration – the combination of evaporation and transpiration
Importance of the hydrological cycle
a. It provides water which is used for domestic, industrial and agricultural purposes
b. It purifies the water
c. It distributes water on the earth
d. It maintains the balance of water between the atmosphere and the surface of the earth
Factors that disrupt/disturb the hydrological cycle
a. Deforestation
This is the removal of vegetation (forests). This practice precludes transpiration process by which water vapour is made available.
It also aggravates soil erosion which results in siltation of water bodies where evaporation process occurs.
b. Poor farming practices such as cultivating along steep slopes and river banks, bush fires encourage soil erosion that leads to siltation of water bodies.
c. Global warming
This refers to the increase in the atmospheric temperature as a result of increase in the greenhouse gases such as carbon dioxide and sulphur. It precludes the process of condensation. As a result, precipitation is not possible.
d. Acid rain
Acid rain is formed from the reaction of water and some gases such as carbon dioxide and sulphur. For instance, the reaction of water carbon dioxide produces carbonic acid, the reaction of water and sulphur produces sulphuric acid. These rains destroy forests (vegetation) which form part of the hydrological cycle.
Ways of maintaining the hydrological cycle
The hydrological cycle can be maintained by the following ways:
a Conserving the water catchment areas by afforestation, reafforestation, enforcement of laws that safeguard forests and civic education aimed to encourage conservation of forests.
b Reducing the emission of fumes from factories and motor vehicles by setting regulatory standards in production as well as usage of motor vehicles.
OCEAN CURRENTS
Ocean currents are referred to as horizontal movement of surface water in oceans at large scale from one point to another point.
They are divided into cold and warm currents. Cold currents flow from polar region to equatorial region and warm currents in a reverse. While cold currents are characterised by low temperatures warm currents are characterised by high temperatures due to temperatures of the regions they originate.
The following are examples of cold ocean currents: Peruvian, Benguela, West Australian, Labrador, Californian, Kamchatka, Canaries and West wind drift.
The following are examples of warm ocean currents: Mozambican, Brazilian, North Atlantic drift, Kuro siwo, East Australian
The map below shows the distribution of ocean currents
Causes of ocean currents
Ocean currents are caused by several factors. The following as some of causing factors:
a Temperature
The variation in temperature between equatorial region and the polar region influences ocean water to move from either region. For instance, some ocean currents move from Polar Regions towards the equator including Peruvian, Benguela, Labrador, Kamchatka, others move from equatorial region towards the poles including Mozambican, Kuro siwo, Brazilian.
b Salinity
Contrasting regions in terms of salinity influences water to flow between the two regions (ie the region of high concentration of salts and that of low concentration of salts). Thus, water flows from region of low concentration of salts to a region of high salt concentration
c Wind
The prevailing winds such as westerlies force water to move from one region to another region. Ocean currents caused by wind are called drifts such as North Atlantic drift and West wind drift.
d Rotation of the earth
This causes deflection of ocean currents, to the left in the southern hemisphere and to the right in the northern hemisphere.
Factors that influence the direction of ocean currents
a. Shape of continents
Continents basically deflect ocean currents which consequently follow the shape of continents such as Peruvian, Benguela, Kuro siwo
b. Wind direction
Ocean currents follow the direction of winds such as the North Atlantic drift and West wind drift.
c. Temperature
Some ocean currents move from polar region (cold region) towards equatorial region (hot region) such as Californian current while others move in the reverse such as Brazilian current
d. Rotation of the earth
This produces a Coriolis force which deflects ocean currents to the right in the northern hemisphere and to the left in the southern hemisphere.
Effects of ocean currents
a They influence fishing activities in regions they affect particularly where two contrasting ocean currents meet such Eastern Canada region (where Labrador and North Atlantic drift meet), North East Asia region (where Kamchatka and Kuro siwo meet). The two regions are world important fishing grounds.
b They modify the climate of the particular region. The Mozambican current warms the east coast of Africa, Californian, Peruvian, Canaries, Benguela have a cooling effect on west coasts of Americas and Africa coasts.
c They distribute the warmth and coldness. Warm currents carry warmth to the Polar Regions and the cold currents have a cooling effect in equatorial regions.
d Ocean currents help in navigation if ships sail in the direction of the currents. On other hand, they retard navigation if ships take the opposite direction of the current.
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