Water on Earth

Question 1

What is interception?

Answer 1

Precipitation that reaches Earth’s surface follows a variety of pathways. The process of
precipitation striking vegetation or other groundcover is called interception

Question 2

How much water dose earths hydrosphere contain?

Answer 2

Earth’s hydrosphere contains about 1.36 billion cubic kilometres of water (more specifically, 1 359 208 000 km3).

Question 3

Where did much of earths water originate from?

Answer 3

Much of Earth’s water originated from icy comets and from hydrogen- and oxygen-laden debris within the planetesimals that coalesced to form the planet.

Question 4

How do the gains and losses of pristine water occure on earth?

Answer 4

Gains occur as pristine water not previously at the surface emerges from within Earth’s crust. Losses occur when water dissociates into hydrogen and oxygen and the hydrogen escapes Earth’s gravity to space or when it breaks down and forms new compounds with other elements.

Question 5

What is Eustasy

Answer 5

Refers to worldwide changes in sea level that are related not to movements of land but rather to changes in the volume of water in the oceans

Question 6

What is the present distribution of all of earths water?

Answer 6

The present distribution of all of Earth’s water between the liquid and frozen states and between fresh and saline, surface and underground, is shown in Figure 9.3. The oceans contain 97.22% of all water, with about 48% of that water in the Pacific Ocean (as measured by ocean surface area; Figure 9.3b). The remaining 2.78% is freshwater (nonoceanic) and is either surface or subsurface water, as detailed in the middle pie chart in the figure.

Question 7

What is the Hydrologic cycle?

Answer 7

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 8

What are the tree main components of the water cycle?

Answer 8

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

Question 9

What is the residence time for a water molecule in the different components of the water cycle?

Answer 9

The residence time for a water molecule in any component of the cycle, and its effect on climate, is variable. 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. 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 10

How do the slower parts of the hydrologic cycle effect during periods of water shortage?

Answer 10

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 11

Definition of evaporation

Answer 11

Evaporation (9)
The movement of free water molecules away from a wet surface into air that is less than saturated; the phase change of water to water vapour

Question 12

What is Transpiration?

Answer 12

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

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 13

What is Evapotransiration?

Answer 13

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 14

What is infiltration?

Answer 14

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 15

What is overland flow or surface runoff?

Answer 15

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.

Question 16

What is streamflow?

Answer 16

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 17

What is percolation

Answer 17

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 18

What is the soil-moisture zone?

Answer 18

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. Within this zone, some water is bound to soil so that it is not available to plants—this depends on the soil texture

Question 19

What is gravitational water, zone of saturation and water table?

Answer 19

If the soil is saturated, then any water surplus within the soil body becomes gravitational water, percolating downward into the deeper groundwater. 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 20

What is base flow?

Answer 20

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 21

What is a water budget?

Answer 21

Water budget (9)
A water accounting system for an area of Earth’s surface using inputs of precipitation and outputs of evapotranspiration (evaporation from ground surfaces and transpiration from plants) and surface runoff. Precipitation “income” balances evaporation, transpiration, and runoff “expenditures”; soil moisture storage acts as “savings” in the budget.

Question 22

What is a Surplus in a water budget?

Answer 22

Surplus (9)
S; the amount of moisture that exceeds potential evapotranspiration; moisture oversupply when soil-moisture storage is at field capacity; extra or surplus water

Question 23

What is a deficit in a water budget?

Answer 23

Deficit (9)
D in a water balance, the amount of unmet (unsatisfied) potential evapotranspiration (PE); a natural water shortage. (See Potential evapotranspiration.

Question 24

What are the components of a water budget?

Answer 24

To understand Thornthwaite’s water-budget methodology and “accounting” procedures, we must first define certain terms and concepts. We begin by discussing water supply, demand, and storage as components of the water-budget equation.

Question 25

What is precipitation?

Answer 25

Precipitation (9)
(Water supply)
Rain, snow, sleet, and hail—the moisture supply; called P in the water balance.

The moisture supply to Earth’s surface is precipitation (P) in all its forms, such as rain, snow, or hail.

Question 26

What is a rain gauge?

Answer 26

Rain gauge (9)
A weather instrument; a standardized device that captures and measures rainfall.

One way to measure precipitation is with a rain gauge, essentially a large measuring cup that collects rainfall and snowfall so the water can be measured by depth, weight, or volume

Question 27

What is potential evapotranspiration?

Answer 27

Potential evapotranspiration (9)

(Water demand!)

PE; the amount of moisture that would evaporate and transpire if adequate moisture were available; it is the amount lost under optimum moisture conditions, the moisture demand. (Compare Actual evapotranspiration.)

Evapotranspiration is an actual expenditure of water to the atmosphere. In contrast, potential evapotranspiration (PE) is the amount of water that would evaporate and transpire under optimum moisture conditions when adequate precipitation and soil moisture are present.

Question 28

What is Actual evapotranspiration?

Answer 28

Actual evapotranspiration (9)
AE; the actual amount of evaporation and transpiration that occurs; derived in the water balance by subtracting the deficit (D) from potential evapotranspiration (PE).

If we subtract the deficit from the potential evapotranspiration, we derive what actually happened—actual evapotranspiration (AE).

Question 29

What is an evaporation pan?

Answer 29

Precise measurement of evapotranspiration is difficult. One method employs an evaporation pan, or evaporimeter. As evaporation occurs, water in measured amounts is automatically replaced in the pan, equalling the amount that evaporated

Question 30

What is a lysimeter?

Answer 30

A more elaborate measurement device is a lysimeter, which isolates a representative volume of soil, subsoil, and plant cover to allow measurement of the moisture moving through the sampled area.

Question 31

What is Soil-moisture storage?

Answer 31

Soil-moisture storage (9)

(Storage)

STRGE; the retention of moisture within soil; it is a savings account that can accept deposits (soil-moisture recharge) or allow withdrawals (soil-moisture utilization) as conditions change.

As part of the water budget, the volume of water in the subsurface soil-moisture zone that is accessible to plant roots is soil-moisture storage (ST). This is the savings account of water that receives deposits (or recharge) and provides for withdrawals (or utilization).

Question 32

What are the three categories of water in the soil-moisture environment?

Answer 32

The soil-moisture environment includes three categories of water—hygroscopic, capillary, and gravitational.

Question 33

Characteristics of hygroscopic, capillary and gravitational water

Answer 33

Only hygroscopic and capillary water remain in the soil-moisture zone; gravitational water fills the soil pore spaces and then drains downward under the force of gravity. Of the two types of water that remain, only capillary water is accessible to plants

Question 34

What is Hygroscopic water?

Answer 34

Hygroscopic water (9)
That portion of soil moisture that is so tightly bound to each soil particle that it is unavailable to plant roots; the water, along with some bound capillary water, that is left in the soil after the wilting point is reached. (See Wilting point.)

Hygroscopic water is inaccessible to plants because it is a molecule-thin layer that is tightly bound to each soil particle by the hydrogen bonding of water molecules.

Question 35

What is the wilting point?

Answer 35

Wilting point (9)
That point in the soil-moisture balance when only hygroscopic water and some bound capillary water remain. Plants wilt and eventually die after prolonged stress from a lack of available water.

Soil moisture is at the wilting point for plants when all that remains is this inaccessible water; plants wilt and eventually die after a prolonged period at this degree of moisture stress.

Question 36

What is Capillary water?

Answer 36

Capillary water (9)
Soil moisture, most of which is accessible to plant roots; held in the soil by the water’s surface tension and cohesive forces between water and soil. (See also Field capacity, Hygroscopic water, Wilting point.)

Capillary water is generally accessible to plant roots because it is held in the soil, against the pull of gravity, by hydrogen bonds between water molecules (that is, by surface tension), and by hydrogen bonding between water molecules and the soil.

Question 37

What is Field Capacity?

Answer 37

Field capacity (9)
Water held in the soil by hydrogen bonding against the pull of gravity, remaining after water drains from the larger pore spaces; the available water for plants. (See Capillary water.)

Most capillary water is available water in soil-moisture storage. After some water drains from the larger pore spaces, the amount of available water remaining for plants is termed field capacity, or storage capacity.

Question 38

What is Gravitational water?

Answer 38

Gravitational water (9)
That portion of surplus water that percolates downward from the capillary zone, pulled by gravity to the groundwater zone.

Gravitational water is the water surplus in the soil body after the soil becomes saturated during a precipitation event. This water is unavailable to plants, as it percolates downward to the deeper groundwater zone. Once the soil-moisture zone reaches saturation, the pore spaces are filled with water, leaving no room for oxygen or gas exchange by plant roots until the soil drains.

Question 39

What is Soil-Moisture utilization?

Answer 39

Soil-moisture utilization (9)
The extraction of soil moisture by plants for their needs; efficiency of withdrawal decreases as the soil-moisture storage is reduced

When water demand exceeds the precipitation supply, soil-moisture utilization—usage by plants of the available moisture in the soil—occurs.

Question 40

What is Soil-moisture recharge?

Answer 40

Soil-moisture recharge (9)
Water entering available soil storage spaces

When water infiltrates the soil and replenishes available water, whether from natural precipitation or artificial irrigation, soil-moisture recharge occurs.

Question 41

What is Permeavility?

Answer 41

Permeability (9)
The ability of water to flow through soil or rock; a function of the texture and structure of the medium.

The property of the soil that determines the rate of soil-moisture recharge is its permeability, which depends on particle sizes and the shape and packing of soil grains.

Question 42

What is the water budget equation?

Answer 42

Moisture supply (precipitation) = [(actual moisture demand)+(Moisture oversupply) + or - Moisture savings)

Question 43

What is outgassing?

Answer 43

Water on Earth was both brought by icy comets and formed within the planet, reaching Earth’s surface in an ongoing process called outgassing