Overview of the hydrologic system for a GE-level course in natural disasters.

1. The Hydrologic System
Photo by W. W. Little
Photo by NASA

2. Hydrologic System
From Okanagan University College, Department of Geography website
• Combination of the atmosphere and the hydrosphere.
• Driven by the Sun and modified by the earth’s rotation.
• Responsible for storms, rivers, lakes, groundwater, sand dunes, glaciers, beaches, soil
formation, oceanic currents, global circulation patterns, climatic belts, and anything thing else
involving water or air.
•Whereas the tectonic system builds things up; the hydrologic system wears them down.
• Primary processes include weathering, erosion, sediment transport, deposition, and lithification

3. States of Matter
Atoms are loosely packed and the
substance conforms to the shape of its
container.
Atoms are closely packed and the
substance maintains its own shape.
Atoms arecompletely separated
and expand to fill all available
space.
From Hamblin & Christiansen (2001)
Matter exists in three forms (states) - solid, liquid, and gas. These represent the ability of
atoms to vibrate and move about. The two primary controls are temperature and pressure. An
increase in temperature adds energy, causing atoms to vibrate and move further apart,
decreasing density. An increase in pressure forces atoms closer together, decreasing their
ability to vibrate and increasing density.

4. Energy Transfer
Conduction: Energy is transferred by direct contact as the
vibration of atoms on the surface of one material is
transmitted to those on the surface of a neighboring material.
Convection: Energy is transferred as material moves from place to
place due to differences in density, caused mostly by contrasts in
temperature. When a material is heated, the atoms move farther apart,
density decreases, and it rises. When the material is cooled, atoms
move closer together, density increases, and it sinks.
Radiation: Energy is transferred through space by electromagnetic
waves.
Most energy is transferred from one substance to another through three processes -
conduction, convection, and radiation. This transfer can often be measured by
changes in temperature.

5. Global Water Distribution
Photo by W. W. Little
Oceans = 97.2%
Photo by Global Marine Drilling
Ice = 2.15%
Photo by W. W. Little Photo by W. W. Little Photo Photo by W. W. Little by W. W. Little
Lakes, streams, ground water, and atmospheric water = 0.65%

6. The Sun
The Sun is the energy source driving the hydrologic system.
Photo by NASA

7. Weather can be though of as what’s happening right now. Climate
deals with long-term weather patterns for a given area. The U.S. has
the most diverse weather of any country on earth and the greatest
number of severe-weather events.
Photo by W. W. Little
Weather vs. Climate
The most important weather measurements include:
• Air temperature
• Air pressure
• Relative humidity
• Type and amount of precipitation
• Type and amount of cloudiness
•Wind velocity (speed & direction) and consistency

8. Atmospheric Compositions
Earth’s present
atmosphere is distinctly
different from that of its
nearest neighbors, Venus
and Mars. Although, it is
believed that at one time,
the atmospheres of these
three planets were much
more alike.

9. Other Atmospheric Constituents
Water vapor: Locally makes up 0 to 4% of atmospheric composition and is important in
heat retention and transfer.
Aerosols: Highly variable in concentration and consist of suspended particles (dust, ash,
smoke, pollen, salt, etc.). Effective in filtering solar energy and provide nucleii for
condensation. Contribute to colorful sunsets.
Ozone: O3 particles located in the stratosphere as a result of the absorption of ultraviolate
radiation by O2 molecules.
Photo by W. W. Little

10. Photo by W. W. Little
Colors in the Sky

11. Solar Radiation
Solar energy moves through the atmosphere by radiation, only part of which
is visible (wavelengths between the infrared and ultraviolate range). Gasses
and aerosols in the atmosphere allow some of this radiation to reach the
earth’s surface, while reflecting, absorbing, or scattering the rest.

12. Fate of Solar Radiation
Photo by NASA
Photo by W. W. Little
Transmission: Radiation energy passes through the atmosphere, eventually reaching the
earth’s surface.
Absorption: Radiation energy is transferred to gasses within the atmosphere, increasing
molecular activity and, therefore, temperature.
Reflection: Radiation is “bounced” off the surface of gasses and aerosols, returning it to
space. An objects reflectivity is referred to as its albedo.
Scattering: Radiation is separated into different wavelengths. Leads to diffuse (indirect)
lighting, soft shadows, blue to white daytime skies, and reddish sun rises and sunsets.

13. “Greenhouse Effect”
About 50% of the solar
radiation that reaches
the atmosphere makes
it to the earth’s surface
The “greenhouse effect” refers to the trapping of solar radiation by
atmospheric gases. Water vapor absorbs five times more radiation than all
other gases combined. Without the “greenhouse effect,” the world would be
a very cold place.

14. Atmospheric Pressure & Temperature
Temperature increases due to
absorption of very short-wave
radiation by N and O at the outer
edge of the atmosphere.
Temperature decreases
because of the thinness of
the atmosphere and a lack
of ozone.
Temperature increases because
of absorption of ultraviolate
radiation by O3.
Temperature decreases
because of atmospheric
thinning.
High heat (energy)
Low temperature
Because of gravitational attraction, most of earth’s atmosphere is
concentrated near the surface in the troposphere, causing both
temperature and pressure to be greater at lower altitudes.

15. Climatic Belts & Temperature
Earth’s surface temperature is greatest at the equator, decreasing to a minimum at the
poles. This disparity in Solar energy distribution is responsible for the generation of
atmospheric and oceanic currents.

16. Temperature and the Sun
Because of earth’s spheroidal shape, a given amount of solar energy is
spread over a larger area at the poles than along the equator.

17. Climatic Belts & Precipitation
The amount of precipitation that falls is strongly tied to latitude. It is
highest at the equator, very low just north and south of the equator,
moderate in mid-latitude regions, and lowest at the poles.

18. Coriollis Effect
Earth’s rotation causes an atmospheric deflection that is clockwise in
the northern hemisphere and counterclockwise in the southern
hemisphere. This creates distinct belts of atmospheric circulation.

19. Earth’s Seasons
24 hrs of light above the
For Northern Hemisphere, day is
24 hrs of light below the
For Northern Hemisphere, night is
Equinox means “equal night”
Sun directly “above” Equator
Arctic Circle
Sun directly “above”
Tropic of Cancer (23.50 N)
Antarctic Circle
Sun directly “above” Tropic
of Capricorn (23.50 S)
longer than night.
longer than day.
Earth’s seasons are due to its axial tilt, causing each hemisphere to face
the Sun during its summer and to face away from the Sun during its
winter. The change in sun angle affects the amount of radiation
reaching the surface at a given spot. The impact is least along the
equator and greatest at the poles.

20. Surface Runoff
Stream channels are the most pervasive surface characteristic of
earth’s continental masses and transport the greatest amount of
continental precipitation back to the sea.
Photo by NASA
Stream channels are to earth what craters are to the moon.

21. Surface Runoff (rivers)
Rivers have a variety of shapes that are controlled by climatic
factors and the nature of the sediment they are transporting.

22. Stream Deposition (deltas)
Photo by W. K. Hamblin
Streams carry both water and sediment (boulders to dissolved
ions in size) from the land to the sea, where the sediment is
ultimately deposited.

23. Glaciers represent a
temporary disruption
of normal surface
runoff. Water is tied
up in ice, which
flows downhill in
much the same
manner as rivers but
much more slowly.
Glaciers

24. Lakes and Reservoirs
Photo by W. K Hamblin
Surface runoff can be temporarily impounded by lakes and
reservoirs.

25. Landslides
Landslides are typically caused by a high moisture content
in earth’s surficial materials.

26. Deserts
Photo by W. W. Little
Deserts represent a disruption of the river system, which occurs when temperatures are
sufficiently high so that the hydrologic system is partially shutoff due to a lack of
precipitation. Eolian (wind) processes dominate and river systems can be completely
overwhelmed by dune fields.

27. Changing Environments
Photos by NASA
Radar images taken through the dune fields of the Sahara Desert by the
space shuttle reveal a well-developed drainage system.

28. Groundwater System
Some precipitation seeps into the
ground and flows through the
subsurface. It can return to the
surface through seeps and springs
or flow directly into streams,
lakes, or the sea.

29. Karst Topography
Photo by W. W. Little
Groundwater dissolves rock and produces karst (dissolved) features,
including sink holes and caves.

30. Shoreline Systems
Rocks are eroded and sediment is transported along shorelines by
waves, tides, and submarine currents.
•Waves: part of the hydrologic system driven by unequal solar heating
(wind).
• Tides: part of the hydrologic system modified by lunar gravitational
attraction.
• Submarine currents: part of the hydrologic system modified by water
chemistry ,temperature, and earth’s rotation.
Photo by W. W. Little

31. Temperature of Seawater
Seawater is mostly cold, but
above freezing. However, a
thin layer of warmer water
exists at the surface, where it is
heated by solar radiation. This
is particularly evident at the
equator.

32. Oceanic Surface Currents
As a result of the Coriollis Effect, ocean surface currents rotate
clockwise in the northern hemisphere and counterclockwise in the
southern hemisphere. These currents have important climatic
implications.

33. Deep Ocean Circulation
Cold, highly saline polar water sinks and moves along the
seafloor, then slowly moves upward where it mixes with warmer
water of mid and low latitudes.

34. Whole Ocean Circulation
Oceanic circulation is very slow, but over time involves mixing of
the entire volume of the sea.