Geoscience Reference
In-Depth Information
the rain gauges. Ho
we
ver, when the range
p
is more structured (an increasing value
of
p
) the value of
λ
tends to fluctuate towards more stable values. These more
stable values are quite similar to Thiessen's weighting coefficients, however, there
is still a large e
n
ough difference between the two sets of values so that a geostatistic
calculation of
λ
is possible.
7.3.2.3.
An evaluation of the rainfall recorded in the drainage basin
There is no simple method that can be used to record the amount of rainfall that
has fallen in a drainage basin. If the linear interpolations of local rainfall are valid,
the estimation of a particular level of rainfall in a drainage basin is equivalent to a
linear combination of such observations. However, weighting coefficients depend
on the spatial structure of rainfall, on the location of the measurement sites, on the
contours of the drainage basin, and on the average values of local rainfall. Only
methods generated from the methods that were introduced much earlier in this
chapter can be used to give objective estimations as averages; this is made possible
by using the geographical information that is available.
7.4. Conclusion
For the foreseeable future hydrologists will not have access to the most relevant
information they require to find a solution to the problems associated with the
estimation of rainfall levels. In order to overcome the challenges, hydrologists need
to use data that provides abundant information on the flow of water at each
measurement site in a drainage basin. Climate data (especially data relating to
rainfall) is the only source of information that can be used to create the variable of
temporal distance. This information can also be used to generate statistical methods
used to estimate rainfall levels for a particular area. The information, which is
produced by the networks of rain gauges, remains local because the methods used to
estimate the amount of rain that falls in a given area (weather radars and remote
sensing) are often imprecise and are limited to small areas. The information that is
provided by the rain gauges relates to a recent period of time; for example the
information that is available rarely dates back to a period of more than 10 years. The
spatial interpolation of rainfall will remain a major concern for hydrologists for the
next few years to come.
The networks of rain gauges that have been developed to record rainfall levels
are not always adapted to the needs of hydrologists. The number of networks
created that are used for research purposes depends on the length of time that the
hydrologists will carry out their research. For example, more networks of rain
gauges will be developed for a longer period of research so that more observations
can be made. The following assumption can be made: the spatial range of rainfall
varies just as the duration of rainfall varies but at a rate that is 0.4 times more
powerful. This means that if a network is used to estimate daily rainfall levels, its
density (which is measured in km
2
) needs to be multiplied by 13 so that hourly
rainfalls can be calculated. Geostatistic analysis makes it possible to compare the
