IB ESS Topic 4.1

Hydrological Cycle

The continuous circulation of water on, above, and below the surface of the Earth.

Hydrosphere

Encompasses all the water on Earth, including oceans, rivers, lakes, groundwater, and atmospheric moisture.

Freshwater

Water with low salt concentration, making up a small fraction (about 2.5%) of Earth's total water.

Groundwater

Water stored beneath the Earth's surface in soil and rock formations.

Aquifers

Underground layers of rock or sediment that hold groundwater.

Surface Runoff

Water flowing over the land surface, typically when the ground is saturated or impermeable.

Infiltration

The process of water seeping into the soil from the surface.

Percolation

The downward movement of water through soil and rock layers, reaching aquifers. Percolation happens after infiltration.

Evaporation

The transformation of liquid water into water vapour, entering the atmosphere from water bodies.

Transpiration

The process of plants releasing water vapour into the atmosphere through stomata in their leaves.

Evapotranspiration

The combined process of evaporation and transpiration.

Condensation

The transformation of water vapour into liquid water, forming clouds or dew.

Precipitation

Water falling from the atmosphere to the Earth's surface as rain, snow, sleet, or hail.

Streamflow

The movement of water in rivers and streams, driven by gravity and the land's slope.

Irrigation

The artificial supply of water to crops, impacting water distribution and availability.

Deforestation

The clearing of forests for various purposes, affecting water absorption, infiltration, and runoff.

Urbanisation

The transformation of natural landscapes into urban areas, altering the hydrological cycle through impermeable surfaces and drainage systems.

Steady State

The balanced condition of a water body where inputs equal outputs, maintaining a constant water level.

Sustainable Water Harvesting

Extracting water at a rate that does not exceed natural replenishment, preserving the steady state.

Unsustainable Water Harvesting

Water extraction exceeding the recharge rate, leading to water depletion and disruption of the steady state.

Sublimation

The transformation of water directly from a solid state (ice or snow) to a gaseous state (water vapour) without passing through the liquid phase.

Advection

The horizontal movement of water vapour or condensed/frozen water droplets (clouds) in the atmosphere, driven by wind.

Melting

The transformation of solid ice or snow into liquid water due to an increase in temperature.

Freezing

The transformation of liquid water into a solid state (ice or snow) due to a decrease in temperature.

Groundwater Flow

The movement of water through the pores and spaces in underground soil and rock layers. This flow is often directed towards rivers, lakes, or oceans.

Impermeable Surfaces

Surfaces like concrete and asphalt that prevent water from infiltrating the soil. These are prevalent in urban areas and contribute to increased surface runoff.

Urban Heat Island Effect

The phenomenon where urban areas experience higher temperatures compared to surrounding rural areas due to the concentration of buildings and paved surfaces. This effect can lead to increased evaporation rates and alter local precipitation patterns.

Water Deficit

A condition that occurs when water outputs from a system (e.g., an aquifer) exceed the inputs, leading to a decrease in water storage. This often results from unsustainable water harvesting practices.

Water Pollution

The contamination of water bodies with substances that negatively impact water quality and ecosystem health. Runoff from agricultural areas carrying fertilizers and pesticides is a significant source of water pollution.

Nutrient Imbalances

Disruptions in the natural balance of nutrients in water bodies. Excessive runoff from agricultural fields, carrying fertilizers, can lead to nutrient imbalances, causing algal blooms and harming aquatic life.