Chapter 10
Water: Hydrologic Cycle and
Human Use
By: Spencer Tungate
A vital resource
• Water is a vital
resource that is
essential to life. Of
the 1.4 billion
cubic kilometers of
water that covers
Earth’s Surface,
only 2.5% of this is
fresh water- water
with a salt content
less than .1%
Developed and Developing Countries
• Developing countries, in contrast to developed
ones, are struggling with water issues. 1.1
billion people still lack access to safe drinking
water and 2.6 do not have access to adequate
sanitation services.
Hydrologic Cycle
• Earth’s water cycle is also known as the
hydrologic cycle. This cycle involves
evaporation, condensation, and precipitation.
Terms of Hydrologic Cycle
• Water vapor- water molecules in a gaseous
state- is the results from evaporation. Also,
humidity is the amount of water vapor in the
air (usually measured in relative humidity).
• Condensation is facilitated by aerosolsmicroscopic liquid or solid particles that
attract water vapor. The processes of
evaporation and condensation create
purification of water.
Hadley Cells
• Convection currents create Hadley cells- the
system composed of rising and falling air. These
cells spill dry air to the north and south of the
equator, creating desserts (Sahara dessert).
Also, rain shadow effects occur in
mountainous areas. This effect creates a dry
region downwind of a mountain range.
Groundwater
• Water that has percolated through the water
(becoming gravitational water) eventually
collects on an impervious layer of rock or
dense clay, creating groundwater. This
groundwater’s upper surfaces are referred to
as the water table. If the water does not
percolate, it is instead capillary water and
returns to the atmosphere through
evapotranspiration.
Water as a resource
• Worldwide, the largest consumptive use for
water is for irrigation (70%), second is for
industry (20%), and third is for direct human
use (10%). 37% comes from groundwater
sources and 63% comes from surface waters
(lakes, streams, reservoirs).
Dams
• Dams provide many
benefits, such as providing
electricity and diverting
water for irrigation and
other uses. However, many
ecological concerns have
been expressed over the
building of dams, such as
the damage to estuaries.
However, dams such as the
Three Gorges Dam, are
making headway by
capturing runoff and aiding
flooding.
Salt problems
• Saltwater intrusion is contaminating many
freshwater sources. Desalination plants are
being built for this intrusion, however, these
plants and technologies are very costly.
Sustainability
• To help provide water for many
parts of the world many steps
must be taken. Using less
water, such as in drip irrigation,
will help water sources to be
diverted to more vital things.
Also, tapping more
groundwater can be a major
source for freshwater.
Municipal systems must be
made that practice
sustainability, such as the
WaterSense commode.
Laws
• Clean Water Act- Allows EPA to develop
programs and rules to carry out its mandate
for oversight of the nation’s water quality, but
not quanitity.
• Many Millennium Development Goals are
targeting freshwater to impoverished
countries.