Hydrological Cycle

Presented By: Architect Md. Mahamudur Rahman Khan Papon Email: ecodesignarch@gmail.com

Water is a transparent and nearly colorless chemical substance that is the main constituent of Earth's streams, lakes, and oceans, and the fluids of most living organisms. Its chemical formula is H2O, meaning that its molecule contains one oxygen and two hydrogen atoms, that are connected by covalent bonds. Water strictly refers to the liquid state of that substance, that prevails at standard ambient temperature and pressure; but it often refers also to its solid state (ice) or its gaseous state (steam or water vapor). It also occurs in nature as snow, glaciers, ice packs and icebergs, clouds, fog, dew, aquifers, and atmospheric humidity.

Definition of Water:

Distribution of water:Ocean – 97%Surface fresh water – 03%• Glaciers – 69%• Underground – 30%• Lakes, Rivers &Swamps – Less then 1%

Use of Water:• Used by human – 1%• Unused – 99%

Water Distribution on Earth Surface

Definition of Hydrological Cycle:

Fig. Hydrological cycle

The water cycle, also known as the hydrological cycle describes the continuous movement of water on, above and below the surface of the Earth. The water moves from one reservoir to another, such as from river to ocean, or from the ocean to the atmosphere, by the physical processes of:

• Evaporation• Condensation• Precipitation• Surface runoff • Infiltration

In doing so, the water goes through different phases: Liquid Solid (ice) and Vapor.

Process of Hydrological cycle:

Evaporation: The transformation of water from

liquid to gas phases as it moves from the ground or bodies of water into the overlying atmosphere. 

The source of energy for evaporation is primarily solar radiation.

90% of the moisture found in the atmosphere is supplied by evaporation.

Only about 10 % of the water evaporated from the oceans is transported over land and falls as precipitation.

Once evaporated, a water molecule spends about 10 days in the air.

Fig. Evaporation

Transpiration:o It is the evaporation of water from

plants through stomata. Stomata are

small openings found on the underside

of leaves that are connected to

vascular plant tissues. In most plants,

transpiration is a passive process

largely controlled by the humidity of the

atmosphere and the moisture content

of the soil.

o 10% of the moisture found in the

atmosphere is released by plants through

transpiration.

Fig. Stomata

Fig. Transpiration

Condensation:o Condensation is the process by which water vapor in the air is changed into

liquid water. o Condensation is crucial to the water cycle because it is responsible for the

formation of clouds.o It is the process whereby water vapour in the atmosphere is returned to its

original liquid state. o In the atmosphere, condensation may appear as clouds, fog, moist, dew or

frost depending upon the physical condition of the atmosphere.

Precipitation: Precipitation is water released

from clouds in the form of rain,

freezing rain, sleet, snow, or hail.

Precipitation occurs when water

vapour in the atmosphere

condenses into clouds and

falls to the earth. It is the primary connection in the

water cycle that provides for the

delivery of atmospheric water

to the Earth. Most precipitation falls as rain.

Run-off: Runoff is the movement of land water to the

oceans, chiefly in the form of rivers, lakes,

and streams. 

Only about 35% of precipitation ends up in

the sea or ocean. The other 65% is

absorbed into the soil. Some of it too will

evaporate.

Everyday about 100 cubic km of water

flows into the seas from the world’s rivers.

The Amazon River, the world’s largest river

provides about 15% of this water.

Run-off is not constant. It decreases during

periods of drought or dry season and

increases during rainy season, storms

and periods of rapid melting of snow and

ice.

Infiltration: Infiltration is the process by which water on the ground surface enters the soil.  Infiltration rate in soil science is a measure of the rate at which soil is able to

absorb rainfall or irrigation. The rate decreases as the soil becomes saturated. If the precipitation rate exceeds the

infiltration rate, runoff will usually occur unless there is some physical barrier. It is related to the saturated hydraulic conductivity of the near-surface soil.

It is measured in inches per hour or millimeters per hour. The rate of infiltration can be measured using an Infiltrometer.

Conclusion:The Hydrologic Cycle is constantly happening all around us each and every day and is an essential part of life. Understanding the global water cycle and how we use water is essential to planning a sustainable source of water for the future. Water is arguably the most important physical resource as it is the one that is essential to human survival. It is necessary so that we have shade from clouds, to water our plants with the falling rain, and for fish to swimming.

Thank you