The water cycle describes how water evaporates from the surface of the earth, rises into the atmosphere as water vapor, condenses into clouds, and falls as precipitation. Most precipitation infiltrates into the ground, where some percolates into streams and groundwater, while the rest runs off directly as surface water into rivers and lakes, eventually flowing back into the oceans to repeat the cycle. The sun provides the energy that drives evaporation and transpiration from plants, which releases water vapor into the air, where it condenses into clouds and falls as rain or snow through precipitation.

1. UNIT-3
ECOLOGY
By: Aishwarya
Assistant Professor
CSE Department
MITS Gwalior

2. WATER CYCLE
Water is essential to life on Earth.
In its three phases (solid, liquid, and gas), water ties together the major parts of the
climate system air, clouds, the ocean, lakes, vegetation, snowpack, and
glaciers.
Earth's water is always in movement, and the natural water cycle, also known as
the hydrologic cycle, describes the continuous movement of water on, above, and
below the surface of the Earth.
Precipitation is a vital component of how water moves through water
cycle, connecting the ocean, land, and atmosphere.
Knowing where it rains, how much it rains and the character of the falling rain,
snow or hail allows scientists to better understand impact on
streams, rivers, surface runoff and groundwater.

3. WATER CYCLE
The water cycle describes how water evaporates from the surface of the earth,
rises into the atmosphere, cools and condenses into rain or snow in clouds, and
falls again to the surface as precipitation
The water falling on land collects in rivers and lakes, soil, and porous layers of
rock, and much of it flows back into the oceans, where it will once more
evaporate. The cycling of water in and out of the atmosphere is a significant aspect
of the weather patterns on Earth

5. MAJOR PROCESS OF WATER CYCLE
EVAPORATION
TRANSPIRATION
CONDENSATION
PRECIPITATION
INFILTRATION & RUNOFF

6. EVAPORATION
Evaporation is the process by which water changes from a liquid to a gas or vapor.
Evaporation is the primary pathway that water moves from the liquid state back
into the water cycle as atmospheric water vapor.
It can be easily visualized when rain puddles on a hot day or when
wet clothes dry in the sun. In these examples, the liquid water is not actually
vanishing it is evaporating into a gas, called water vapor.
Evaporation happens on a global scale.
Evaporation accounts for 90 percent of the moisture in the atmosphere.

7. EVAPORATION
Substances can exist in three main states: solid, liquid, and gas. Evaporation is just
one way a substance, like water, can change between these states.
Melting and freezing are two other ways. When liquid water reaches a low enough
temperature, it freezes and becomes a solid ice.
When solid water is exposed to enough heat, it will melt and return to a liquid. As
that liquid water is further heated, it evaporates and becomes a gas water vapor.
In the water cycle, evaporation occurs when sunlight warms the surface of the
water. The heat from the sun makes the water molecules move faster and faster,
until they move so fast they escape as a gas.
Once evaporated, a molecule of water vapor spends about ten days in the air.

8. TRANSPIRATION
Transpiration is the evaporation of water through minute pores, or stomata, in the
leaves of plants. For practical purposes, transpiration and the evaporation from all
water, soils, snow, ice, vegetation, and other surfaces are lumped together and
called evapotranspiration, or total evaporation.
Most of the water absorbed by the roots of a plant as much as 99.5 percent is
not used for growth or metabolism; it is excess water, and it leaves the plant
through transpiration. Transpiration is very important for maintaining moisture
conditions in the environment.
Transpiration occurs because plants take in more water than they actually need at a
given time. It is a way of getting rid of excess water.
When water is removed from the plant, it can more easily access the carbon
dioxide that it needs for photosynthesis. Also, plants can use transpiration as a
method of cooling themselves.

9. TRANSPIRATION
Transpiration is part of the water cycle, also known as the hydrological cycle. The
water cycle describes how water moves throughout the Earth. First, water
transpires from plants and enters the atmosphere as water vapor.
Evapotranspiration (ET) is the sum of water evaporation and transpiration from a
surface area to the atmosphere. Evaporation accounts for the movement of water
to the air from sources such as the soil, canopy interception, and water bodies.

10. CONDENSATION
The transition process from the vapor state to the liquid state is called
condensation. Condensation may take place as soon as the air contains more water
vapor than it can receive from a free water surface through evaporation at the
prevailing temperature.
Condensation is crucial to the water cycle because it is responsible for the
formation of clouds.
Condensation is the opposite of evaporation.
Condensation is responsible for ground-level fog, for your glasses fogging up
when you go from a cold room to the outdoors on a hot, humid day, for the water
that drips off the outside of your glass of iced tea, and for the water on the inside
of the windows in your home on a cold day.

11. PRECIPITATION
Precipitation is water released from clouds in the form of rain, freezing rain, sleet,
snow, or hail. 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.
Precipitation that falls to the Earth is distributed in four main ways:
some is returned to the atmosphere by evaporation, some may be intercepted by
vegetation and then evaporated from the surface of leaves, some percolates into
the soil by infiltration, and the remainder flows directly as surface runoff into the
sea.
Some of the infiltrated precipitation may later percolate into streams as
groundwater runoff.
Precipitation is a major component of the water cycle, and is responsible for most
of the fresh water on the planet.
Most groundwater is derived from precipitation that has percolated through the
soil.

12. PRECIPITATION
The driving force of precipitation and the water cycle in general is the solar energy
from the Sun. Earth maintains a delicate balance of radiative energy by reflecting
approximately one third of the incoming solar radiation, and emitting the
remaining two-thirds that are absorbed as infrared radiation back to space.

13. INFILTRATION & RUNOFF
Infiltration is the process by which water on the ground surface enters the soil. It is
commonly used in both hydrology and soil sciences. The infiltration capacity is
defined as the maximum rate of infiltration.
Runoff occurs when there is excessive precipitation and the ground is saturated
cant absorb anymore water.
Rivers & lakes are the result of runoff. There is some evaporation from runoff into
atmosphere but for the most part water in rivers and lakes return to the oceans