Michael Acreman, Freshwater Management Adviser to the
IUCN, Institute of Hydrology, United Kingdom
Water, the Environment, and Population
Water is the lifeblood of our planet. It is fundamental to
the biochemistry of all living organisms. The planet's ecosystems are
linked and maintained by water, and it drives plant growth, provides a
permanent habitat for many species (such as 8,500 species of fish), and
is a breeding ground or temporary home for others, including most of the
worlds 4,200 species of amphibians and reptiles described so far. Water
is also a universal solvent and provides the major pathway for the flow
of sediment, nutrients and pollutants. Through erosion, transportation
and deposition by rivers, glaciers, and icesheets, water shapes the
landscape and through evaporation it drives the energy exchange between
land and the atmosphere, thus controlling the Earth's climate.
Apart from a few minor chemical processes, water is neither created nor
destroyed, it only moves from place to place and changes in quality. The
total amount of water on Earth is 1.4 billion cubic kilometers
(km3), but only around 41,000 km3 circulates
through the hydrological cycle, the remaining being stored for long
periods in the oceans, ice caps and aquifers. Furthermore, the renewal
rate provided by rainfall varies around the world. In the Atacama desert
in southern Peru it almost never rains, whilst 6,000 millimeters (mm) of
rain per year is not uncommon in parts of New Zealand. In any one place
rainfall also varies from year to year.
