Environmental Engineering Reference
In-Depth Information
the ecosystem, and the distribution of vegetation, fauna and population owes much to the
pattern of rainfall.
For these reasons, and because of its ultimate importance to human activities, a great
deal of attention has been paid to measuring, mapping and predicting precipitation. As we
have seen, scarcity of data, particularly in the less accessible parts of the world, limits our
ability to gain an accurate picture of precipitation inputs. On the whole, however, rainfall
is one of the easiest components of the hydrological cycle to measure. Conversely,
evapotranspiration is one of the more difficult. Empirical formulas are the most
frequently used ways of obtaining the information.
KEY POINTS
1
Precipitation is found in a variety of forms. Which form reaches the ground surface will
depend upon many factors: surface temperature, atmospheric moisture, method and
rate of cooling and intensity of updraughts, for example. Each type of precipitation has
its own characteristics and consequences. The distribution of precipitation varies
greatly in time and space, and in quantity.
2
Evaporation and transpiration are more complex processes which return moisture to the
atmosphere. The rate of evapotranspiration will depend largely on two factors, (a) how
moist the ground is and (b) the capacity of the atmosphere to absorb the moisture.
Hence the greatest rates are over the tropical oceans, where moisture is always
available and the long hours of sunshine and steady trade winds evaporate vast
quantities of water.
FURTHER READING
Jackson, I. J. (1989)
Climate, Water and Agriculture in the Tropics
, Harlow: Longman (chapters 1-
4). Primarily concerned with the tropics, rainfall is examined in terms of its origins, seasonality,
variability and intensity. Intermediate level.
Linacre, E. (1992)
Climate Data and Resources: a reference and guide
, London: Routledge
(chapters 2-3). A useful reference on measuring and estimating climatic elements. Provides
considerable detail.
Shaw, E. M. (1994)
Hydrology in Practice
, third edition, London: Chapman & Hall. A popular
topic giving a practical approach to the problems of measuring and calculating
evapotranspiration. Intermediate level and requires some mathematical expertise.
Sumner, G. (1988)
Precipitation: process and analysis
, Chichester: Wiley. An extensive survey of
all elements of precipitation from its methods of formation in the atmosphere to how
precipitation data can be analysed to draw meaningful conclusions. Intermediate to advanced
level but very readable.
Ward, R. C., and Robinson, M. (2000)
Principles of Hydrology
, London: McGraw-Hill. Now into
its fourth edition, this has proved popular as a text on aspects of the hydrological cycle.
Intermediate level.
