oration of excessive irrigation water, a process that can
eventually render soil incapable of supporting crops.

siltation - occurs when water channels and reservoirs become
clotted with silt and mud, a side effect of deforestation and soil
erosion.

slash-and-burn agriculture - a rotating cultivation technique in
which trees are cut down and burned in order to clear land for
temporary agriculture; the land is used until its productivity declines
at which point a new plot is selected and the process repeats; this
practice is sustainable while population levels are low and time is
permitted for regrowth of natural vegetation; conversely, where these
conditions do not exist, the practice can have disastrous consequences
for the environment .

soil degradation - damage to the land's productive capacity
because of poor agricultural practices such as the excessive use of
pesticides or fertilizers, soil compaction from heavy equipment, or
erosion of topsoil, eventually resulting in reduced ability to produce
agricultural products.

soil erosion - the removal of soil by the action of water or wind,
compounded by poor agricultural practices, deforestation, overgrazing,
and desertification.

ultraviolet (UV) radiation - a portion of the electromagnetic
energy emitted by the sun and naturally filtered in the upper
atmosphere by the ozone layer; UV radiation can be harmful to living
organisms and has been linked to increasing rates of skin cancer in
humans.

water-born diseases - those in which the bacteria survive in, and
is transmitted through, water; always a serious threat in areas with an
untreated water supply.

Environment - international agreements
This entry separates country participation in international
environmental agreements into two levels - party to and signed but not
ratified. Agreements are listed in alphabetical order by the
abbreviated form of the full name.

Environmental agreements
This information is presented in Appendix C: Selected International
Environmental Agreements, which includes the name, abbreviation, date
opened for signature, date entered into force, objective, and parties
by category.

Ethnic groups
This entry provides a rank ordering of ethnic groups starting with the
largest and normally includes the percent of total population.

Exchange rates
This entry provides the official value of a country's monetary unit at
a given date or over a given per