Geology Reference
In-Depth Information
3
Calibration of Erosion Models
V.G. JETTEN
1
AND M.P. MANETA
2
1
Department of Earth Systems Analysis, International Institute of Geoinformation
Science and Earth Observation, Enschede, The Netherlands
2
Geosciences Department, University of Montana, Missoula, MT, USA
3.1 Introduction
from the fact that the first widely used soil loss
model, the Universal Soil Loss Equation (USLE),
was based on a regression analysis of data from
several hundred experimental plots installed by
the USDA Soil Conservation Service, and so a
close link between theory and experimental data
has always been a focal point. Later attempts at
improving the modelling by including more proc-
ess descriptions, and including spatial variability
with the use of Geoinformation Science, have not
changed that fact.
Jetten and Favis-Mortlock (2006) gave an over-
view of 16 water erosion models used in Europe
at a range of scales from several square metres to
the whole continent, and concluded that calibra-
tion and validation attempts are done for all mod-
els on all scales, which is encouraging. There
exist several dozens of published water erosion
models in the world, as well as models that have
been made for a different purpose, such as river
basin models that have a sediment component.
The purpose of the modelling closely dictates
exactly what it is we are calibrating. The term
'erosion modelling' is used to indicate the total
detachment of soil particles by rainfall and run-
off in an area, but also to predict the soil loss
from a specific area. In a wider context it is used
to indicate the hazard or risk associated with
the removal of topsoil, both onsite (fertility loss,
gullying) and offsite (muddy floods and down-
stream pollution). Often erosion modelling is
done to simulate the effects of a change in land
use, application of soil conservation measures,
A dictionary may define the term calibration as
“the act of checking or adjusting the accuracy of
a measuring instrument, by comparison with a
standard”. For instance, a ruler can be calibrated
against the standard length of 1 metre, which was
defined in 1791 by the French Academy of
Sciences as the 10
−7
part of the distance along the
Earth's surface from pole to Equator (later
this definition changed). The mathematicians
Delambre and Méchain supervised the measure-
ments of the length of France along the meridian
through Paris as a section of the circumference of
the Earth. The standard metre, they deduced from
their measurements, appeared to be only 0.2 mm
short compared with a later satellite-based deter-
mination of the circumference of the Earth. This
story has all the elements important for the cali-
bration of an erosion model: the tuning of a model
to predict observed (or perceived) 'true' values of
erosion, using limited data to deduce the work-
ings of the entire system, with errors that may
occur for various reasons and with newer meth-
ods that may improve the result and improve our
insight. Fortunately, calibration and improve-
ment of erosion models has been a major focus of
model users and model builders from the begin-
ning of erosion modelling. This stems perhaps
