The Hydrologic Cycle

Question 1

What is the Hydrologic Cycle?

Answer 1

Hydrologic cycle (9)
A simplified model of the flow of water, ice, and water vapour from place to place. Water flows through the atmosphere and across the land, where it is stored as ice and as groundwater. Solar energy empowers the cycle

Question 2

What three main components can the water cycle be divided into?

Answer 2

The water cycle can be divided into three main components: atmosphere, surface, and subsurface.

Question 3

What is the average residence time for water in the atmosphere?

Answer 3

Water has a short residence time in the atmosphere—an average of 10 days—where it plays a role in temporary fluctuations in regional weather patterns.

Question 4

What is the residence time of water in the deep ocean, groundwater and glacial ice?

Answer 4

Water has longer residence times in deep-ocean circulation, groundwater, and glacial ice (as long as 3000–10 000 years), where it acts to moderate temperature and climatic changes.

Question 5

What effect can the slower parts of the hydrologic cycle play during periods of water shortage?

Answer 5

These slower parts of the hydrologic cycle, the parts where water is stored and released over long periods, can have a “buffering” effect during periods of water shortage.

Question 6

How much of earths evaporation occurs in the oceans?

Answer 6

More than 97% of Earth’s water is in the oceans, and it is over these water bodies that 86% of Earth’s evaporation occurs.

Question 7

Definition of evaporation

Answer 7

evaporation is the net movement of free water molecules away from a wet surface into air that is less than saturated.

Question 8

What is transpiration?

Answer 8

Transpiration (9)
The movement of water vapour out through the pores in leaves; the water is drawn by the plant roots from soil-moisture storage.

During transpiration, plants release water to the atmosphere through small openings called stomata in their leaves. Transpiration is partially regulated by the plants themselves, as control cells around the stomata conserve or release water.

Question 9

What is the evaporation potential of a tree/forest?

Answer 9

On a hot day, a single tree can transpire hundreds of litres of water; a forest, millions of litres.

Question 10

What is Evapotranspiration?

Answer 10

Evapotranspiration (9)
The merging of evaporation and transpiration water loss into one term. (See Potential evapotranspiration, Actual evapotranspiration.)

Evaporation and transpiration from Earth’s land surfaces together make up evapotranspiration, which represents 14% of the water entering Earth’s atmosphere

Question 11

Where dose the bulk of continental precipitation come from?

Answer 11

Clearly, the bulk of continental precipitation comes from the oceanic portion of the cycle. The different parts of the cycle vary over different regions on Earth, creating imbalances that, depending on the local climate, lead to water surpluses in one place and water shortages in another.

Question 12

What are the two basic pathways that the precipitation reaches Earth’s surface?

Answer 12

Precipitation that reaches Earth’s surface as rain follows two basic pathways: It either flows overland or soaks into the soil.

Question 13

What is Interception?

Answer 13

Interception (9)
A delay in the fall of precipitation toward Earth’s surface caused by vegetation or other ground cover.

In which precipitation lands on vegetation or other ground cover before reaching the surface.

Question 14

What is Stem Flow?

Answer 14

Intercepted water that drains across plant leaves and down their stems to the ground is known as stem flow.

Question 15

What is Throughfall?

Answer 15

Precipitation that falls directly to the ground, including drips from vegetation that are not stem flow, is throughfall.

Question 16

What is infiltration?

Answer 16

Infiltration (9)
Water access to subsurface regions of soil moisture storage through penetration of the soil surface.

After reaching the ground surface as rain, or after snowmelt, water may soak into the subsurface through infiltration, or penetration of the soil surface

Question 17

What is Overland flow / surface runoff?

Answer 17

If the ground surface is impermeable (does not permit the passage of liquids), then the water will begin to flow downslope as overland flow, also known as surface runoff.

Overland flow (9)
Surplus water that flows across the land surface toward stream channels. Together with precipitation and subsurface flows, it constitutes the total runoff from an area.

Surface runoff (9)
Surplus water that flows across the ground surface toward stream channels when soils are saturated or when the ground is impermeable; also called overland flow.

Question 18

What is streamflow?

Answer 18

Excess water may remain in place on the surface in puddles or ponds, or may flow until it forms channels—at this point it becomes streamflow, a term that describes surface water flow in streams, rivers, and other channels.

Question 19

How much of the water in the cycle is moving on or through land?

Answer 19

8% of the water in the cycle is moving on or through land. Most of this movement—about 95%—comes from surface waters that wash across land as overland flow and streamflow.

Question 20

What is percolation?

Answer 20

Percolation (9)
The process by which water permeates the soil or porous rock into the subsurface environment.

Water that infiltrates the subsurface moves downward into soil or rock by percolation, the slow passage of water through a porous substance

Question 21

What is the Soil-Moisture zone.

Answer 21

Soil-moisture zone (9)
The area of water stored in soil between the ground surface and the water table. Water in this zone may be available or unavailable to plant roots, depending on soil texture characteristics.

The soil-moisture zone contains the volume of subsurface water stored in the soil that is accessible to plant roots.

Question 22

How much precipitation over land infiltrates’ the subsurface, and what percentage of that water returns to the atmosphere either by evaporation from soil or transpiration from plants?

Answer 22

An estimated 76% of precipitation over land infiltrates the subsurface, and about 85% of this water returns to the atmosphere either by evaporation from soil or transpiration from plants.

Question 23

What is gravitational water?

Answer 23

If the soil is saturated, then any water surplus within the soil body becomes gravitational water, percolating downward into the deeper groundwater.

Question 24

What is the zone of saturation and the water table?

Answer 24

The latter defines the zone of saturation, where the soil spaces are completely filled with water. The top of this zone is known as the water table.

Question 25

What is Base flow?

Answer 25

Base flow (9)
The portion of streamflow that consists of groundwater.

At the point where the water table intersects a stream channel, water naturally discharges at the surface, producing base flow, which refers to the portion of streamflow that consists of groundwater.

Question 26

Where do streams and groundwater flw into?

Answer 26

Under natural conditions, streams and groundwater ultimately flow into oceans, thus continuing movement through the hydrologic cycle. In some cases, streams flow into closed lake basins, where water evaporates or soaks into the ground. Many streams flow into reservoirs behind dams, where water is stored until it evaporates or is released into the channel downstream.