The hydrologic cycle describes the continuous movement of water on, above, and below the surface of the Earth. Water is evaporated from oceans and land surfaces, rises into the atmosphere, cools and condenses to form clouds, and falls again as precipitation. Some precipitation runs off surfaces and becomes surface water in oceans, seas, rivers, lakes, and groundwater; other precipitation is intercepted by trees and vegetation; and some infiltrates and recharges groundwater stores. Water is also transpired into the atmosphere from plants and other surfaces. The hydrologic cycle involves the balanced circulation of water in the hydrosphere, atmosphere, geosphere, and biosphere.

1. The hydrologicThe hydrologic
cycle and watercycle and water
resource ofresource of
worldworld

2. • Hydrology means the science of the water. It isHydrology means the science of the water. It is
the science that deals with the occurrence ,the science that deals with the occurrence ,
circulation and distribution of water o of thecirculation and distribution of water o of the
earth and its atmosphere.earth and its atmosphere.
• Hydrology is a very broad subject of an inter –Hydrology is a very broad subject of an inter –
disciplinary nature drawing support from allieddisciplinary nature drawing support from allied
sciences such as meteorology, geology , statistics ,sciences such as meteorology, geology , statistics ,
chemistry, physics and fluid mechanics.chemistry, physics and fluid mechanics.

3. World water balance and waterWorld water balance and water
resource of the earth by unesco 1975resource of the earth by unesco 1975

4. OceanOcean
StorageStorage
Wat er Source Wat er Vol ume
(cu. m i.)
Wat er Vol ume
(cu. k m)
% of T otal Wat er
Oceans 321,000,000 1,338,000,000 96.5%
Total global wat er 332,500,000 1,386,000,000 --
Gleick, P. H., 199 6: Water resources. In Encyclopedia of Climate and Weath er, ed. by S. H. Schneider, Oxfo rd
University Press, New York, vol. 2, pp.817-82 3.

6. How much groundHow much ground
water?water?• Ground water occurs
only close to the
surface (a few miles
down)
• Density of soil/rock
increases with
depth
• The weight of the
rocks above
condense the rocks
below and squeeze
out the open pore
spaces deeper in the

7. Frozen freshwater storedFrozen freshwater stored
in glaciers, ice fields, andin glaciers, ice fields, and
snowfieldssnowfields
• Glacial ice covers 11%Glacial ice covers 11%
of all landof all land
• Represents a large % ofRepresents a large % of
all freshwaterall freshwater
• Mountain snowfieldsMountain snowfields
are “reservoirs” forare “reservoirs” for
many water-supplymany water-supply
systemssystems
• 75% in Western States75% in Western States
• ““Rain-on-snow” eventsRain-on-snow” events
contribute to highcontribute to high
runoff velocitiesrunoff velocities
• ““New” OperationalNew” Operational
Snowmelt ForecastsSnowmelt Forecasts

8. What percent of theWhat percent of the
Earth’s total volumeEarth’s total volume
of water is stored inof water is stored in
the atmosphere?the atmosphere?
• 0.001%0.001%
• Water vaporWater vapor
• CloudsClouds
(water vapor(water vapor
condensed oncondensed on
particulate)particulate)

9. Global Hydrological CycleGlobal Hydrological Cycle
• The various aspects of water related to the earth can beThe various aspects of water related to the earth can be
explained in terms of a cycle Known asexplained in terms of a cycle Known as HydrologicalHydrological
cycle.cycle.
• The sunThe sun provides the energy for the evaporation of theprovides the energy for the evaporation of the
sea water and gravitational field and coriolis forcesea water and gravitational field and coriolis force
contribution to the circulation of water.contribution to the circulation of water.

11. PrecipitationPrecipitation
• The vapor that accumulates or freezes onThe vapor that accumulates or freezes on
condensation nuclei is acted on by gravitycondensation nuclei is acted on by gravity
and falls to Earth’s surface.and falls to Earth’s surface.
rain, freezing rain, sleet, snow, or hail

12. InterceptionInterception
Interception: when it rains over a catchment, not all theInterception: when it rains over a catchment, not all the
precipitation falls directly on to the ground. Before itprecipitation falls directly on to the ground. Before it
reaches the ground, a part of it may be caught by thereaches the ground, a part of it may be caught by the
vegetation and subsequently evaporated. The volume ofvegetation and subsequently evaporated. The volume of
water so caught is called interception.water so caught is called interception.
1.1.It maybe retained the vegetation as surface storage and returned toIt maybe retained the vegetation as surface storage and returned to
the atmosphere by evaporation a process termed interception loss.the atmosphere by evaporation a process termed interception loss.
2. It can be drip off the plant leaves to join the ground surface or the2. It can be drip off the plant leaves to join the ground surface or the
surface flow , this is known as through fall .surface flow , this is known as through fall .
3. The rain water may run along the leaves and branches and down the3. The rain water may run along the leaves and branches and down the
stem to reach the ground surface .This is called stem flow.stem to reach the ground surface .This is called stem flow.

14. Depression storageDepression storage
• Depression StorageDepression Storage: when the precipitation of a storm: when the precipitation of a storm
reaches the ground, it must fill- up all depressions beforereaches the ground, it must fill- up all depressions before
it can flow over the surface. The volume of water tappedit can flow over the surface. The volume of water tapped
in these depression is called depression storage.in these depression is called depression storage.
• Depression storage depends on these chief factorsDepression storage depends on these chief factors
• 1.the type of soil, 2. the condition of the surface1.the type of soil, 2. the condition of the surface
reflecting the amount and the nature of depression,3. thereflecting the amount and the nature of depression,3. the
slope of the catchment , 4.the antecedent precipitationslope of the catchment , 4.the antecedent precipitation
as a measure of soil moisture.as a measure of soil moisture.

15. InfiltationInfiltation
• Infiltration: is the flow of water into the ground throughInfiltration: is the flow of water into the ground through
the soil surfacethe soil surface..
• At the top , a thin layer of saturated zone is created .At the top , a thin layer of saturated zone is created .
• Beneath zone there is a transition zone.Beneath zone there is a transition zone.
• The next zone is transmission zone where the downwardThe next zone is transmission zone where the downward
moisture takes place.moisture takes place.
• The last zone is the wetting zone . The soil moistureThe last zone is the wetting zone . The soil moisture
zone will be at or near the field capacity and the moisturezone will be at or near the field capacity and the moisture
content decreased with the depthcontent decreased with the depth..

16. RunoffRunoff
• Runoff: is draining or flowing of precipitation from aRunoff: is draining or flowing of precipitation from a
catchment area through a surface channel. It thuscatchment area through a surface channel. It thus
represents the output from the catchment in a given unitrepresents the output from the catchment in a given unit
of time.of time.

17. InterflowInterflow
• Interflow: A part of precipitation that infiltrates movesInterflow: A part of precipitation that infiltrates moves
laterally through upper layer of the soil and returns to thelaterally through upper layer of the soil and returns to the
surface at some location away from the point of entry insurface at some location away from the point of entry in
to the soil.(through flow).to the soil.(through flow).

18. EvaporationEvaporation
•The process by which liquid water is
transformed into a gaseous state
•Evaporation into a gas ceases when the gas
reaches saturation
•The molecules that escape the condensed stage have
above-average energies.
•Those left behind have below-average energies
•Manifested by a decrease in the temperature of the
condensed phase.

19. EvaporationEvaporation

20. TranspirationTranspiration
• Transpiration: is the process by which water leaves theTranspiration: is the process by which water leaves the
body of a living plant and reaches the atmosphere asbody of a living plant and reaches the atmosphere as
water vapour.The water is taken up by the plant-rootwater vapour.The water is taken up by the plant-root
system and escapes through the leaves.system and escapes through the leaves.
• The important factors effectinng transpiration are :The important factors effectinng transpiration are :
1.pressure,2. temperature,3. wind,4. light intensity,4.1.pressure,2. temperature,3. wind,4. light intensity,4.
characteristics of the plant such as root and leaf systemcharacteristics of the plant such as root and leaf system
of the plant.of the plant.

21. TranspirationTranspiration

22. Process ofProcess of
hydrological cyclehydrological cycle
• Water of the oceans evaporated due to heat energyWater of the oceans evaporated due to heat energy
provided by the solar radiation .provided by the solar radiation .
• The water vapors move upwards and forms clouds . WhileThe water vapors move upwards and forms clouds . While
much of the clouds condense and fall back to the oceansmuch of the clouds condense and fall back to the oceans
and land as precipitation. Some part of it may evaporateand land as precipitation. Some part of it may evaporate
back to the atmosphere even falling .back to the atmosphere even falling .
• Another part may be intercepted by vegetation, structureAnother part may be intercepted by vegetation, structure
and other surfaces modification, or some part move down toand other surfaces modification, or some part move down to
the ground surface.the ground surface.
• A portion of water that reaches the ground enters the earth'sA portion of water that reaches the ground enters the earth's
surface through infiltration enhances the moisture content ofsurface through infiltration enhances the moisture content of
the soil and reach the groundwater body.the soil and reach the groundwater body.

24. • Vegetations sends a portion of the water from under theVegetations sends a portion of the water from under the
ground surface back to the atmosphere through theground surface back to the atmosphere through the
process of transpiration.process of transpiration.
• The precipitation reaching the ground surface afterThe precipitation reaching the ground surface after
meeting the needs infiltration and evaporation movesmeeting the needs infiltration and evaporation moves
downward the natural slope over the surfaces and troughdownward the natural slope over the surfaces and trough
a network of gullies , streams and rivers to reach thea network of gullies , streams and rivers to reach the
ocean.ocean.
• The ground water may come to the surface throughThe ground water may come to the surface through
springs and other outlets after spending a considerablysprings and other outlets after spending a considerably
longer time than he surface flow.longer time than he surface flow.
• The portion of the precipitation which by a variety ofThe portion of the precipitation which by a variety of
paths above and below the surface of the earth reachespaths above and below the surface of the earth reaches
the stream channel is call runoff.the stream channel is call runoff.
• Once it enters a stream channel runoff becomes streamOnce it enters a stream channel runoff becomes stream
flow. It is seen that the hydrologic cycle is a very vast andflow. It is seen that the hydrologic cycle is a very vast and
complicated cycle.complicated cycle.

25. • Thank youThank you