Rural population refers to the portion of a country’s population that resides in rural areas, which are typically defined as areas outside of urban centers, cities, and towns. Rural areas are characterized by lower population densities, agricultural activities, and a greater reliance on natural resources for livelihoods.
The definition of rural population can vary depending on the country, as different countries may have different definitions and criteria for what constitutes a rural area. In general, rural populations tend to be more dispersed, have lower levels of income and education, and have limited access to healthcare and other basic services compared to urban populations.
In many developing countries, a significant portion of the population lives in rural areas and depends on agriculture for their livelihoods. The rural population is often composed of small-scale farmers, agricultural laborers, and other rural workers engaged in activities such as forestry, fishing, and mining.
Lakes may be classified according to the mode of origin of the hollows which contain their waters.
These include the following categories: by earth movement, by erosion, by deposition, by volcanic activity and artificially by man.
Earth movements cause lake formation when there is subsidence or warping of the land. Hollows or depression so formed in the earth’s crust may contain water and hence lakes. This is most easily seen in rift valleys. Example of a rift valley lake is Tanganyika while a good example of a down warped lake is Lake Victoria.
Erosional lakes are as a result of different erosional activities. E.g. Ice sheets and valley glaciers may scoop out hollows to form a basin and when water collects it create a lake known as tarns, cirque lake or ribbon lake.
Lakes produced by deposition. Barriers across a river valley hold back the water which forms a lake. Again Oxbow lake (e.g. Lake Kanyaboli) are formed from the meanders of rivers. The deposition of silt at the two ends of ‘Ox-bow’ closes the channel between the main river and its old loop. Last, sometimes large estuaries are partially filled with silt. In the portions not so filled are large shallow lagoons (lakes).
Lakes produced by vulcanicity. They lakes are often formed by the accumulation of water in the crater of extinct volcanoes. The best example is Lake Toba in northern Sumatra whereas a local example in Kenya is Lake Simbi in Nyanza province.
Man-made lakes. These are lakes that are deliberately formed by building a dam across a river valley for the purpose of generating hydroelectricity and/or for irrigation.
water is stored in the seas as a liquid. high temperature and warm winds change liquid water into a gas (water vapour) which rises into the atmosphere.
evaporation involves the change in the state of moisture form or liquid form (water) to the gaseous state (water vapour)
the radiant energy provided by the sun causes the molecules of water in the liquid form to move about more rapidly.
these activated molecules eventually move fast enough to break free from the liquid surface and pass to the atmosphere in the gaseous state.
in doing so they take with them their energy of molecular motion called kinetic energy. the temperature of the remaining liquid is lowered by the removal of energy and it may be considered as a cooling process.
each year some 360000km3 of water is evaporated from the oceans and seas into the atmosphere
evaporation rate depend on
temperature
relative humidity: the ability of water to accept water vapour
wind speed
vegetation: evaporation rates are higher when the evaporation cover is denser that is a larger amount of water is intercepted by leaves and will eventually be lost through evaporation
in the tropical rainforest
the rate of evaporation, though high is lower than in tropical deserts because the cloud cover reduces the energy input
in the tropical desert
the evaporation rate is high due to clear sunny, skies and low relative humidity
in the tundra
the evaporation rate is low because of the low temperature
evapotranspiration
this is the compound loss of water by direct evaporation from water on the surface of vegetation, soil and lands, and from transpiration from plants
vegetation not only intercept rainfall but also take it up through roots from the soil
this water is eventually returned to the atmosphere by transpiration from leaves
surface water is also evaporated from leaves
evapotranspiration represents the sum of water loss from both plant and other sources
it is dependent on meteorological factors such as duration of direct sunshine, solar energy flux, wind speed and air moisture content
two forms of evapotranspiration
potential evapotranspiration
this is the maximum amount of moisture that can be lost from the soil by evaporation and transpiration if there is a continuous supply of water to the soil to make up for losses.
such conditions apply under irrigation or in very wet equatorial land
actual evapotranspiration
this is the actual amount of soil moisture lost to the atmosphere by plants and soil
this loss is limited by the amount of moisture available in the soil and is less than the potential loss
although the water deficit and water surplus in the soil are important for plant growth, they also affect the level of water available for the surface hydrological process.
the relative amount of water can be estimated from the soil moisture budget graph
soil water deficit
when there is insufficient rainfall, where rainwater is less than potential evapotranspiration because the soil water supply is restricted, the soil may be dry for a long period of time
the potential evapotranspiration is greater than actual evaporation. the plants can transpire more moisture than is supplied by precipitation
therefore, they draw upon the accumulated soil water, but this is inadequate to allow them to transpire as much as they could
soil water surplus
where there is abundant rainfall, the precipitation exceeds the losses of moisture through evapotranspiration.
the plants can not transpire all the moisture which is supplied by precipitation
in many places, the two rates are the same if rainfall is equal or exceeds the potential evapotranspiration.
annual actual evapotranspiration can in no case exceed annual potential evapotranspiration which is already the maximum possible amount of evapotranspiration loss
condensation and precipitation
the constant and continuous supply of moisture from the surface to the atmosphere is balanced by an equal return of moisture in the opposite direction through the processes of condensation and precipitation
condensation
this process involves a change in the state of the moisture from the gaseous form to the liquid form
the rapidly moving molecules of the water vapour gas are slowed down by colliding with each other and with other condensation nuclei in the air (for example dust and salt particles), thus forming into water droplets
as the molecules are slowed down, their kinetic energy, originally derived from the radiant energy of the sun during evaporation, is converted into heat energy therefore condensation is the heating process
condensation occurs when the temperature of the air falls to the level known as dew point, which may be defined as the temperature at which the air is 100% saturated with water vapour.
raindrops are formed around the condensation nuclei. cloud is formed
as the raindrops become bigger and bigger precipitation occurs
precipitation
this applies to all forms of moisture (for example rain, snow, hail, frost) which reach the earth from the atmosphere
precipitation occurs when cloud droplets (0.01mm in diameter are coalesced to form raindrops (0.02mm in diameter) and becomes to heavy to be suspended
the annual precipitation intensity, amount and seasonality ( the length of humid season and the portion of the precipitation total falling in the humid season) are determinants of the amount of discharge in the river within the river basin
tropical thunderstorm downpours are often very localized that is the effects are limited on the scale of the individual catchments. however, steady depression rainfall may affect extensive drainage basins
in the tropical rainforest
tropical rainforest has hot, humid climate and the precipitation is heavy that is over 2000 mm per year.
as warm air is uplift and becomes unstable, cumulonimbus clouds are formed
in tropical desert
tropical desert climate has a hot, arid climate and the precipitation is small that is less than 250mm per year
as warm air is sink and become stable under the subtropical high-pressure belt, the sky is clear no clouds are developed
in the tundra forest
tundra forest has a cold climate and the annual precipitation is low that is between 250mm to 500mm, in the form of snow, which had little effect on the surface hydrological process
the melting of snow is slow and hence only a small amount of water is contributed to the drainage basin
interceptions
some rainfall is intercepted by plants and trees before reaching the ground.
some fall on the land and infiltrate the ground or flow on the surface as small fast-flowing streams.
vegetation is capable of catching or trapping (intercepting) incoming precipitation and can store water temporarily before they finally reach the ground
if the precipitation continues the storage spaces of leaves and branches become filled and water drips through the canopy as throughfall
water will also reach the ground surface by running down trees trunks as stemflow
factors affecting interception
extent of vegetation cover (density): if the vegetation cover is denser, the amount of interception will be increased. for example the amount of interception is higher in tropical rainforest (30% of the precipitation). however the savanna can only get 15% of precipitation
types of vegetation: for example forest can intercept more precipitation than grass cover
duration, magnitude and amount of rainfall
duration of storm
if the storm lasts a short time, a considerable proportion of the rainfall remains caught on the leaves and branches, this is called interception storage
if the storm lasts for a long period, the amount of interception will be increased. however, the ability of absorption will decrease because the body of vegetation is wet enough
magnitude of storm
if the magnitude (intensity) of the storm is great, the amount of interception will be smaller
amount of storm
if the amount of storm (rainfall) is great, the amount of interception will decrease
in other words, precipitation falling onto vegetated area can follow three possible routes
reaching the ground as throughfall in between the space unoccupied by branches, stems and foliage of plants
being caught by branches, stems and foliage of plants and eventually reaching the ground as stemflow
being caught by branches, stems and foliage of plants and returned directly to the atmosphere by evaporation
in the rainforest
much of the precipitation does not fall directly onto the ground, making interception by the dense vegetation the highest among the world’s landscape
in the tropical deserts
the sparse vegetation means that the interception is very small. most of the precipitation reaches the ground directly
in the tundra
the sparse and low height of vegetation also means there is little interception in the tundra climate
the low interception rates of tropical deserts and tundra lead to the high proportion of water being available (80%-100%) for surface hydrological processes.
however, the actual amount of water available in the tropical deserts and tundra is very low because of the low precipitation rate and also the quick of conversion of snow into hard ice in the tundra
overland flow
upland streams flow downhill and join at the confluence to form slower moving wider, deep rivers which eventually discharges the water into lakes or sea
