Hydrological Cycle

MICRO-REALM 01

The Hydrosphere

71%

• Water covers 71% of the Earth's surface
• Makes Earth uniquely habitable ("The Blue Planet")
• Total water volume is constant; it only changes form/location

MICRO-REALM 02

Global Distribution (97/3)

97.2% SALINE OCEANS

3%

• 97.2% of all water is in the Oceans (Saline)
• Only ~2.8% is Freshwater
• Most freshwater is entirely inaccessible to humans

MICRO-REALM 03

Freshwater Breakdown

68.7% ICE CAPS & GLACIERS30.1% GROUNDWATER0.3% SURFACE LAKES/RIVERS

• Of the tiny 2.8% freshwater slice:
• Over two-thirds is frozen in Antarctica/Greenland
• Groundwater is the largest accessible reservoir!

MICRO-REALM 04

The Hydrological Cycle

CONTINUOUS CIRCULATIONWATER BETWEEN EARTH SPHERES

• The continuous exchange of water between the
• Oceans, Atmosphere, Land surface, and Subsurface
• Never stops, has no true beginning or end

MICRO-REALM 05

The Solar Engine

☀

• Solar radiation is the primary energy source
• Provides the massive heat required to evaporate water
• Lifting it against gravity into the atmosphere

MICRO-REALM 06

Gravity: The Return Force

GRAVITY PULLS WATER DOWNPRECIPITATION & RUNOFF

• If the sun lifts water up, gravity pulls it down
• Drives precipitation, surface river flow, and
• Deep percolation into groundwater aquifers

MICRO-REALM 07

Global Hydrological Balance

GLOBAL EVAPORATION =GLOBAL PRECIPITATION

• Annually, total evaporation equals total precipitation
• However, over oceans: Evaporation > Precipitation
• Over land: Precipitation > Evaporation (Runoff balances it)

MICRO-REALM 08

Evaporation (Liquid $\to$ Gas)

↑↑

• Phase change from liquid water to gaseous vapour
• Primarily from the vast surface of the Oceans
• Absorbs Latent Heat of Vaporisation (cooling the surface)

MICRO-REALM 09

Transpiration

↑

• Release of water vapour from plant leaves (stomata)
• Acts as a biological pump, pulling deep soil water
• Critical humidity source over dense rainforests (Amazon)

MICRO-REALM 10

Evapotranspiration (ET)

EVAPORATION (SOIL)+TRANSPIRATION (PLANTS)

• Combined total moisture loss from a land surface
• Potential ET (PET): Max possible loss if water was unlimited
• Actual ET (AET): Real loss based on available water

MICRO-REALM 11

Sublimation

→

↑

• Direct conversion of solid ice/snow into water vapor
• Bypasses the liquid melting phase entirely
• Occurs in dry, cold, windy environments (e.g., Himalayas)

MICRO-REALM 12

Advection (Transport)

→

• Horizontal transport of atmospheric moisture by winds
• Moves massive amounts of ocean vapour over landmasses
• Creates the "Atmospheric Rivers" that cause floods

MICRO-REALM 13

Condensation & Precipitation

VAPOR → WATER DROPSRELEASES HEAT

• Cooling air reaches saturation $\to$ Condensation (Clouds)
• Droplets coalesce and fall back to Earth as Precipitation
• Returns atmospheric water to the surface

MICRO-REALM 14

Interception (Canopy Catch)

|

• Precipitation that lands on vegetation/tree leaves
• Much of it evaporates back to the atmosphere
• Before it ever touches the ground (reduces flood spikes)

MICRO-REALM 15

Surface Runoff

• Water flowing horizontally over the land surface
• Occurs when rain exceeds the soil's infiltration capacity
• The primary agent of fluvial erosion and river feeding

MICRO-REALM 16

Watershed / Catchment Area

TOPOGRAPHIC BASIN DRAININGINTO A SINGLE RIVER SYSTEM

• The total land area that drains runoff into a specific river
• Separated from adjacent basins by a ridge (Watershed Divide)
• Fundamental unit of hydrological management

MICRO-REALM 17

Streamflow & Discharge

Q = AREA × VELOCITY
(CUMECS)

• Runoff channeled into streams and rivers
• Discharge is the volume of water passing a point per second
• Measured in Cubic Meters per Second (Cumecs)

MICRO-REALM 18

Lakes & Reservoirs (Storage)

TEMPORARY SURFACE STORAGE

• Natural lakes or man-made dams pause the runoff
• Allowing sediment to settle and water to evaporate
• Slows the return journey of water to the oceans

MICRO-REALM 19

Infiltration (Entering Soil)

|

SOIL MOISTURE

• The process of water seeping INTO the ground surface
• High in sandy, vegetated soils; low in clay/asphalt
• Creates critical soil moisture for agriculture

MICRO-REALM 20

Percolation (Deep Movement)

DEEP DOWNWARD SEEPAGETOWARDS AQUIFERS

• Not to be confused with infiltration!
• Percolation is the deep downward movement of water
• Through rock/soil layers to recharge groundwater

MICRO-REALM 21

Zone of Aeration (Vadose)

PORES: AIR + WATER

• Upper soil/rock layer below the surface
• Pore spaces contain both air and water
• Plant roots draw moisture from this unsaturated zone

MICRO-REALM 22

The Water Table

WATER TABLE BOUNDARY

• The precise boundary separating the Vadose Zone above
• From the Saturated Zone below
• Rises during monsoons, drops during droughts/pumping

MICRO-REALM 23

Zone of Saturation (Phreatic)

ALL PORE SPACES100% FILLED WITH WATER

• Lower zone below the water table
• Every pore space, crack, and fissure is filled with water
• This water is technically defined as "Groundwater"

MICRO-REALM 24

Aquifers (Permeable Rock)

SANDSTONE / LIMESTONE / GRAVEL

• Permeable rock layers that store and transmit groundwater
• Must have high porosity (space) and permeability (flow)
• The source of water for wells and boreholes

MICRO-REALM 25

Aquicludes (Impermeable)

SOLID CLAY / SHALE (NO FLOW)

• Impermeable rock layers (like clay or solid granite)
• They may hold water (high porosity) but block its flow (low permeability)
• Trap aquifers above or below them

MICRO-REALM 26

Groundwater Flow

VERY SLOW HORIZONTAL SEEPAGECENTIMETERS PER DAY

• Groundwater doesn't sit still; it moves horizontally
• Driven by gravity and pressure (hydraulic head)
• Extremely slow compared to rivers (cm/day)

MICRO-REALM 27

Springs

💧

• Occurs where the Water Table intersects the land surface
• Groundwater naturally flows out onto the ground
• Often feeds the headwaters of mountain rivers

MICRO-REALM 28

Artesian Wells

💧

• Confined aquifer trapped between two aquicludes
• Water is under high hydrostatic pressure
• When drilled, water gushes to the surface without pumping!