The Water Cycle and Climates © Lisa Michalek

The Water (Hydrologic) Cycle Earth has a limited supply of water This supply is constantly being recycled between the oceans, atmosphere, and land

The Water Cycle During the recycling of water, water enters the atmosphere by evaporation and transpiration Transpiration is the process where living plants release water vapor to the atmosphere Of the precipitation that falls on Earth’s surface 50% returns to the atmosphere by evaporation 18% infiltrates (sinks into) the ground (groundwater) 32% is surface runoff that enters lakes and rivers

Groundwater Zone of saturation The Water Table All spaces, cracks and other openings in soil and rock grains become completely filled with water Water will stop sinking into the soil once it has reached a layer of solid rock that it cannot pass through The Water Table Boundary between the zone of aeration and the zone of saturation

Groundwater The amount of water in the ground and the movement of water through the ground are controlled by the characteristics of the soil and rock found near the surface Almost all materials on Earth’s surface are porous

Porosity The number of pores in a material compared with its volume The porosity (percent of empty space) determines how much air or water a sample of rock can hold Particle size alone does not affect the porosity of a soil

Permeability The ability of a soil to transmit water The rate (how fast water can pass through a soil) depends on the size of the pores and how the pores are connected Surface runoff occurs when rainfall exceeds the permeability of a soil, when a soil is saturated, or when the slope (gradient) of a soil’s surface is too great to allow infiltration to occur

Capillarity The ability of a soil to draw water upward into tiny spaces between soil grains Soils composed of very small particles show the most capillary uptake This is because these soils have more surface area per unit volume for water to cling to them than do soils with large particles Capillary water moves upward against the force of gravity because of the attraction between water molecules and the surfaces of the soil particles

Rainfall and Stream Flow Streams and rivers do not respond immediately to rainfall Most precipitation falls on the ground and then must flow over the land as runoff to reach a stream A time lag occurs between maximum precipitation and maximum stream discharge

Factors Affecting Stream Flow Slow falling precipitation Low gradient of the land Vegetation blocks overland flow Large rivers respond slowly because most runoff must flow a great distance to reach the rivers Small streams and streams in mountain areas where the land is steep and rocky respond quickly to rainfall Runoff is very rapid and very brief in regions with buildings, paved streets, and parking lots

Watersheds (Drainage Basin) The geographic area that drains into a particular stream or other body of water Bounded by a drainage divide, usually a line of high land, across which streams do not flow

How Heat Energy Travels Convection is heat flow by density currents within a fluid Uneven heating of Earth’s surface by the sun causes winds

How Heat Energy Travels Conduction is a form of heat flow that occurs when a hot substance comes in contact with a cooler substance The vibrational energy of the warmer atoms and molecules is transferred to the cooler atoms and molecules, making them vibrate more

How Heat Energy Travels Earth’s primary source of energy is the sun Radiation is the flow of energy as electromagnetic waves, such as visible light It is the fastest form of heat transfer All radiation travels at the speed of light, 300,000,000 meters per second

Insolation Earth receives nearly all of its energy from the sun The sun’s electromagnetic energy that reaches the earth is called insolation (INcoming SOLar radiATION) The intensity (strength) of insolation depends on several factors Angle Duration Type of surface

Angle of Insolation A measure of how high the sun is in the sky As the sun rises and sets, this angle changes This angle is measured from the horizon up to the position of the sun The noon sun has the greatest angle of insolation The angle also changes seasonally

Angle of Insolation Because Earth is spherical, each latitude has a different angle of insolation

Duration of Insolation The length of time (from sunrise to sunset), or daylight period, that the sun appears in the sky A section of Earth’s surface receives the most heat energy when the sun is highest in the sky and when the duration of insolation is the greatest As the angle of insolation and the duration of insolation increases, the temperature at Earth’s surface increases

Variations in Day Length

Variations of Insolation

Absorption of Insolation Upon reaching the Earth’s surface, visible light waves are absorbed, scattered, or reflected Light-colored objects reflect most of the light that falls on them Dark-colored objects absorb most of the light that falls on them Some of the absorbed energy is changed into infrared heat waves that reradiated back into the atmosphere at night

Absorption of Insolation

Reflection of Insolation When light is reflected, it bounces off a surface Clouds reflect about half of the light falling on them The lower the angle of insolation, the greater the reflection of solar rays More reflection also occurs when the land is light in color or covered by snow or ice

Reflection of Insolation

Terrestrial Radiation Energy waves emitted from Earth’s surface are longer in wavelength than energy waves emitted from the sun The longer heat waves radiated by Earth are absorbed by gases and remain trapped in the atmosphere This process is called the greenhouse effect

Greenhouse Effect

Insolation Temperature Lag A time lag exists between the time of greatest intensity of insolation and the time of highest air temperature This is because insolation energy is first absorbed by Earth’s surface and then reradiated as heat energy that warms the air

Climate Unlike weather, the climate for a large geographical region is based on the atmospheric conditions measured over a long period of time The average conditions of temperature and precipitation and the annual distribution of these conditions characterize a region’s climate

Factors that Affect Climate Latitude The location is an important factor that determines the average local temperatures Altitude High-altitude locations have cool climates because of the cooling of air as it moves to higher elevations Mountain Ranges Can modify precipitation and temperature patterns

Factors that Affect Climate Oceans and Large Bodies of Water Because of its specific heat, water heats up and cools down more slowly than land areas The climates of locations near the ocean or other large bodies of water are more moderate than inland climates Coastal and marine climates are cooler in the summer and warmer in the winter than are inland climates

Factors that Affect Climate Ocean Currents Air above an ocean current is affected by the surface temperature of the water Cool water will cool the air, and warm water will warm the air

Factors that Affect Climate Planetary Wind Belts Prevailing winds are important in determining the effect of ocean currents on nearby climates There are various regions of rising (low-pressure systems) and sinking (high- pressure systems) air currents

Factors that Affect Climate Monsoons producing Rainy weather Typical Storm Tracks US Weather systems usually move from west to east