The hydrologic The hydrologic cycle and water cycle and water

resource of worldresource of world

• Hydrology means the science of the water. Hydrology means the science of the water. It is the science that deals with the It is the science that deals with the occurrence , circulation and distribution of occurrence , circulation and distribution of water o of the earth and its atmosphere.water o of the earth and its atmosphere.

• Hydrology is a very broad subject of an Hydrology is a very broad subject of an inter – disciplinary nature drawing support inter – disciplinary nature drawing support from allied sciences such as meteorology, from allied sciences such as meteorology, geology , statistics , chemistry, physics and geology , statistics , chemistry, physics and fluid mechanics.fluid mechanics.

World water balance and water resource of World water balance and water resource of the earth by unesco 1975the earth by unesco 1975

Ocean Ocean StorageStorage

Water Source Water Volume(cu. mi.)

Water Volume(cu. km)

% of Total Water

Oceans 321,000,000 1,338,000,000 96.5%Total global water 332,500,000 1,386,000,000 --Gleick, P. H., 1996: Water resources. In Encyclopedia of Climate and Weather, ed. by S. H. Schneider, OxfordUniversity Press, New York, vol. 2, pp.817-82 3.

How much ground How 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 Earth

Frozen freshwater stored in Frozen freshwater stored in glaciers, ice fields, and glaciers, ice fields, and

snowfieldssnowfields• Glacial ice covers 11% of Glacial ice covers 11% of

all landall land• Represents a large % of all Represents a large % of all

freshwaterfreshwater• Mountain snowfields are Mountain snowfields are

“reservoirs” for many “reservoirs” for many water-supply systemswater-supply systems• 75% in Western States75% in Western States

• ““Rain-on-snow” events Rain-on-snow” events contribute to high runoff contribute to high runoff velocitiesvelocities

• ““New” Operational New” Operational Snowmelt ForecastsSnowmelt Forecasts

What percent of the What percent of the Earth’s total volume of Earth’s total volume of water is stored in the water is stored in the

atmosphere?atmosphere?• 0.001%0.001%

• Water vapor Water vapor • CloudsClouds

(water vapor (water vapor condensed on condensed on particulate)particulate)

Global Hydrological CycleGlobal Hydrological Cycle• The various aspects of water related to the earth The various aspects of water related to the earth

can be explained in terms of a cycle Known as can be explained in terms of a cycle Known as Hydrological cycle.Hydrological cycle.

• The sun The sun provides the energy for the evaporation provides the energy for the evaporation of the sea water and gravitational field and of the sea water and gravitational field and coriolis force contribution to the circulation of coriolis force contribution to the circulation of water.water.

PrecipitationPrecipitation• The vapor that accumulates or freezes The vapor that accumulates or freezes

on condensation nuclei is acted on by on condensation nuclei is acted on by gravity and falls to Earth’s surface.gravity and falls to Earth’s surface.

rain, freezing rain, sleet, snow, or hail

InterceptionInterceptionInterception: when it rains over a catchment, not all Interception: when it rains over a catchment, not all

the precipitation falls directly on to the ground. the precipitation falls directly on to the ground. Before it reaches the ground, a part of it may be Before it reaches the ground, a part of it may be caught by the vegetation and subsequently caught by the vegetation and subsequently evaporated. The volume of water so caught is evaporated. The volume of water so caught is called interception.called interception.

1.1.It maybe retained the vegetation as surface storage and It maybe retained the vegetation as surface storage and returned to the atmosphere by evaporation a process returned to the atmosphere by evaporation a process termed interception loss.termed interception loss.

2. It can be drip off the plant leaves to join the ground surface 2. It can be drip off the plant leaves to join the ground surface or the surface flow , this is known as through fall .or the surface flow , this is known as through fall .

3. The rain water may run along the leaves and branches and 3. The rain water may run along the leaves and branches and down the stem to reach the ground surface .This is called down the stem to reach the ground surface .This is called stem flow. stem flow.

Depression storageDepression storage• Depression StorageDepression Storage: when the precipitation of : when the precipitation of

a storm reaches the ground, it must fill- up all a storm reaches the ground, it must fill- up all depressions before it can flow over the surface. depressions before it can flow over the surface. The volume of water tapped in these depression The volume of water tapped in these depression is called depression storage.is called depression storage.

• Depression storage depends on these chief Depression storage depends on these chief factors factors

• 1.the type of soil, 2. the condition of the surface 1.the type of soil, 2. the condition of the surface reflecting the amount and the nature of reflecting the amount and the nature of depression,3. the slope of the catchment , 4.the depression,3. the slope of the catchment , 4.the antecedent precipitation as a measure of soil antecedent precipitation as a measure of soil moisture.moisture.

InfiltationInfiltation• Infiltration: is the flow of water into the ground Infiltration: is the flow of water into the ground

through the soil surfacethrough the soil surface..• At the top , a thin layer of saturated zone is At the top , a thin layer of saturated zone is

created .created .• Beneath zone there is a transition zone.Beneath zone there is a transition zone.• The next zone is transmission zone where the The next zone is transmission zone where the

downward moisture takes place.downward moisture takes place.• The last zone is the wetting zone . The soil The last zone is the wetting zone . The soil

moisture zone will be at or near the field capacity moisture zone will be at or near the field capacity and the moisture content decreased with the and the moisture content decreased with the depthdepth..

RunoffRunoff• Runoff: is draining or flowing of precipitation from Runoff: is draining or flowing of precipitation from

a catchment area through a surface channel. It a catchment area through a surface channel. It thus represents the output from the catchment in thus represents the output from the catchment in a given unit of time.a given unit of time.

InterflowInterflow• Interflow: A part of precipitation that infiltrates Interflow: A part of precipitation that infiltrates

moves laterally through upper layer of the soil moves laterally through upper layer of the soil and returns to the surface at some location away and returns to the surface at some location away from the point of entry in to the soil.(through from the point of entry in to the soil.(through flow).flow).

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.

EvaporationEvaporation

TranspirationTranspiration• Transpiration: is the process by which water Transpiration: is the process by which water

leaves the body of a living plant and reaches the leaves the body of a living plant and reaches the atmosphere as water vapour.The water is taken atmosphere as water vapour.The water is taken up by the plant-root system and escapes through up by the plant-root system and escapes through the leaves.the leaves.

• The important factors effectinng transpiration are The important factors effectinng transpiration are :1.pressure,2. temperature,3. wind,4. light :1.pressure,2. temperature,3. wind,4. light intensity,4. characteristics of the plant such as intensity,4. characteristics of the plant such as root and leaf system of the plant.root and leaf system of the plant.

TranspirationTranspiration

Process of hydrological Process of hydrological cyclecycle

• Water of the oceans evaporated due to heat energy Water 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 . The water vapors move upwards and forms clouds . While much of the clouds condense and fall back to While much of the clouds condense and fall back to the oceans and land as precipitation. Some part of it the oceans and land as precipitation. Some part of it may evaporate back to the atmosphere even falling . may evaporate back to the atmosphere even falling .

• Another part may be intercepted by vegetation, Another part may be intercepted by vegetation, structure and other surfaces modification, or some structure and other surfaces modification, or some part move down to the ground surface.part move down to the ground surface.

• A portion of water that reaches the ground enters A portion of water that reaches the ground enters the earth's surface through infiltration enhances the the earth's surface through infiltration enhances the moisture content of the soil and reach the moisture content of the soil and reach the groundwater body.groundwater body.

• Vegetations sends a portion of the water from under the Vegetations sends a portion of the water from under the ground surface back to the atmosphere through the ground surface back to the atmosphere through the process of transpiration.process of transpiration.

• The precipitation reaching the ground surface after The precipitation reaching the ground surface after meeting the needs infiltration and evaporation moves meeting the needs infiltration and evaporation moves downward the natural slope over the surfaces and trough downward the natural slope over the surfaces and trough a network of gullies , streams and rivers to reach the a network of gullies , streams and rivers to reach the ocean.ocean.

• The ground water may come to the surface through The ground water may come to the surface through springs and other outlets after spending a considerably springs 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 of The portion of the precipitation which by a variety of paths above and below the surface of the earth reaches paths 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 stream Once it enters a stream channel runoff becomes stream flow. It is seen that the hydrologic cycle is a very vast flow. It is seen that the hydrologic cycle is a very vast and complicated cycle.and complicated cycle.

• Thank youThank you