WATER AND CLIMATE

UNIT

8

I. Water

The water cycle, also called the hydrologic cycle, is a model used to illustrate the movement and phase changes of water at and near the Earth’s surface.

This cycle is fueled by insolation.

The ultimate source of most of the water on land is the evaporation of the ocean waters.

Water retention is when precipitation is stored as ice or snow or on the leaves of trees or other plants.

Infiltration is when precipitation sinks into the earth. All of the water found beneath the earth’s surface is called subsurface water.

Runoff is precipitation that does not infiltrate; it flows over the surface of the earth.

Evaporation (the addition of water vapor into the atmosphere from ground and surface water) along with transpiration (the addition of water vapor into the atmosphere from plants undergoing photosynthesis) are the source of all atmospheric water vapor

Evapotranspiration is the name given to these combined processes.

Factors influencing infiltration

1. Slope of the land

2. Degree of saturation

3. Porosity

4. Permeability

5. Capillarity

6. Vegetation

7. Land use

As slope increases, infiltration decreases.

As the pore spaces between the solid particles of the earth become filled with water, the land becomes saturated and infiltration decreases.

The structure of the earth is distinguished by the amount of water that is present.

The lowest portion in which the pore spaces are completely filled with water is the Zone of Saturation

The upper portion in which the pore spaces are partly filled with air and partly filled with water is called the Zone of Aeration.

The interface between these two portions is called the water table.

The subsurface water beneath the water table is called ground water.

As precipitation occurs, the water infiltrates through the Zone of Aeration down to the water table causing the depth of the water table to decrease.

As ground water evaporates, the depth of the water table increases

Porosity is the percentage of open space in a material in comparison to its total volume. As the percentage of open space (pores and cracks) increases, the total amount of infiltration increases.

Well-rounded particles have a greater porosity because they don’t fit together very well.

The more closely packed together the particles are, the lower the porosity.

When a sample contains particles of approximately the same size, it is said to be sorted.

If a sample contains a mixture of particle sizes, it is said to be unsorted.

As the amount of sorting increases,

the porosity increases

and

infiltration increases

Permeability is the ability of a material to allow for infiltration.

The more interconnected the pore spaces are, the greater the permeability.

Capillarity is the upwards movement of water caused by the attractive forces between the water molecules and the surrounding Earth materials.

The smaller the particles, the greater the capillarity.

In general, as vegetation increases, the amount of infiltration increases as well.

Human activities such as:• development• farming• grazing of livestock• cutting down trees/ clearing

vegetation

reduces the amount of vegetation causing the amount of infiltration to decrease.

Factors that cause run-off

1. Rate of precipitation is greater than the rate of infiltration

2. Pore spaces are saturated

3. Slope is steep

4. Presence of surface water

Stream discharge is the amount of water flowing past any given point in a stream.

Flooding occurs when stream discharge increases to the point that the stream overflows its bed or channel.

Flooding

The first rule when dealing with a flood is to move to higher ground.

Communities should have a planned evacuation route in preparation for flood emergencies

II. Climate

Climate is the overall view of a regions’ weather conditions over a long period of time.

Temperature and moisture are the two characteristics described in a regions’ climate

A region is arid (dry) if the amount of precipitation is less than the amount of evapotranspiration…

moisture in is less than moisture out!

A region is humid (wet) if the amount of precipitation is greater than the amount of evapotranspiration…

moisture in is more than moisture out

Factors influencing climate

Low latitudes have high intensity of insolation, therefore they tend to have higher temperatures.

Higher latitudes have lower intensity of insolation, therefore they tend to have lower temperatures.

Large bodies of water moderate temperature resulting in cooler summers and warmer winters compared to the extreme temperatures experienced at the same latitude inland.

Surface ocean currents modify coastal climates.

Currents flowing away from the equator are warm.

Currents flowing towards the equator come from higher latitudes and are cool.

As elevation increases, temperature decreases and precipitation increases.

This change in temperature and moisture is caused by a phenomenon known as adiabatic temperature change.

The windward side of a mountain is cool and moist. The leeward side of a mountain is hot and dry.

This is due to the adiabatic temperature change that occurs when air rises or falls due to the influence of the mountain.

As the vegetation in an area decreases, temperature increases and moisture levels decrease.

Urbanization and deforestation cause hot, dry climates.

The period of time during which glaciers advance into mid-latitude regions is called an ice age. The period of time between ice ages, during which the temperature increases is called an inter-glacial warming period

The End!