|
1. Definition
| Name |
EROSIVITY
(RDI) |
| Brief
definition |
The
power of overland flow runoff to erode soil material. This is
partly a property of the rainfall, and partly of the soil surface. |
| Unit
of measure |
mm² |
| Spatial scale |
|
| Temporal scale |
|
2. Position
within the logical framework DPSIR
3. Target and
political pertinence
| Objective |
To
provide a measure of the effectiveness of rainfall to erode
soil, for a given topography and soil type. It is used in the
PESERA/RDI model to estimate Erosion Risk. |
| Importance
with respect to desertification |
Erosion
by running water occurs where the intensity and duration of
rainstorms exceeds the capacity of the soil to infiltrate the
rain. Increased erosivity indicates greater erosive power of
the overland flow. Where rainfall is intense, it is particularly
urgent to adopt conservation and management methods to ensure
that the soil is well protected in the rainy season. |
| International
Conventions and agreements |
The
UNCCD emphasizes that combating desertification must be tackled
within the general framework of actions to promote sustainable
development. |
| Secondary
objectives of the indicator |
May
be mapped separately to indicate erosive power, although actual
erosion risk depends on the balance between erosive power and
soil resistance. |
4. Methodological
description and basic definitions
| Definitions
and basic concepts |
In the PESERA/RDI model,
the runoff threshold is an estimate of the depth of daily
rainfall which can infiltrate before overland flow runoff
occurs. If this threshold depth is h, then the
erosivity of a single storm of total rainfall r
is defined as (r-h)². Over a period of
a month, the combined erosivity is defined as
where f(r)
is the frequency of storm rainfall r. For periods
longer than a month, the value of the threshold h should
generally be updated monthly. Within each month it is recommended
that the distribution of daily rainfalls is fitted to a Gamma
distribution,
where
is the mean rain per rain-day and 
is its variance.
|
| Benchmarks
Indication of the values/ranges of value |
The
parameter α in the gamma distribution usually lies in the
range 0.5<α <1.0, so that the maximum total erosivity
value (corresponding to zero runoff threshold h)
is α R
where R is the total rainfall. The minimum erosivity
is close to zero, corresponding to high runoff thresholds. Values
can therefore lie in the range 0 – 10,000 mm². |
| Methods
of measurement |
As
indicated from the definition, erosivity is estimated from rainfall
characteristics, together with a knowledge of the annual cycle
of variation in the runoff threshold (which has typical values
from 5 – 100 mm). |
| Limits
of the indicator |
The
indicator should be viewed with caution in areas and seasons
subject to snowmelt or frozen ground. It is applicable only
to erosion by running water. This indicator is not the same
as the rainfall erosivity in the USLE. |
| Linkages
with other indicators |
Erosion
risk (RDI), Runoff
threshold (RDI), Soil
erosion (USLE)
|
5. Evaluation
of data needs and availability
| Data
required to calculate the indicator |
Storm
amount for an individual storm erosivity. A long (>10 year)
record of daily rainfalls for average annual or monthly values.
Soil and land use maps, preferably interpreted in the light
of local knowledge, are required to estimate the runoff threshold. |
| Data
sources |
Necessary
data are usually available and accessible to researchers, but
meteorological data may be expensive. |
| Availability
of data from national and international sources |
Data
can be obtained from various regional, national or international
institutions involved in the collection and the analysis of
metorological and soils data. |
6. Institutions
that have participated in developing the indicator
| Main institutions
responsible |
University
of Leeds |
| Other
contributing organizations |
Catholic
University of Leuven, Agricultural Univ of Athens, ISRIC Wageningen,
CSIC/EEZA Almeria, INRA Orleans, Universities of Basilicata,
Lisbon and Murcia. |
7. Additional
information
| Bibliography
|
Kosmas,
C., Kirkby, M. and Geeson, N. 1999. Manual on: Key indicators
of desertification and mapping environmentally sensitive areas
to desertification. European Commission, Energy, Environment
and Sustainable Development, EUR 18882, 87 |
| Other
references |
Kirkby,
M.J., Y. Le Bissonais, T.J. Coulthard, J. Daroussin and M.L.
McMahon, 2000. The development of Land Quality Indicators for
Soil Degradation by Water Erosion. Agriculture, Ecosystems and
Environment, 81, 125-36
Kirkby, M.J., Jones, R.J.A.,
Irvine, B., Gobin, A, Govers, G., Cerdan, O., Van Rompaey,
A.J.J., Le Bissonnais, Y., Daroussin, J., King, D., Montanarella,
L., Grimm, M., Vieillefont, V., Puigdefabregas, J., Boer,
M., Kosmas, C., Yassoglou, N., Tsara, M., Mantel, S., Van
Lynden, 2004. G. Pan-European Soil Erosion Risk Assessment:
The PESERA Map, Version 1 October 2003. Explanation of Special
Publication Ispra 2004 No.73 (S.P.I.04.73). European Soil
Bureau Research Report No.16, EUR 21176, 18pp. Office for
Official Publications of the European Communities, Luxembourg.
|
| Contacts
Name and address |
Mike
Kirkby, School of Geography, University of Leeds, LS2 9JT, UK
mike@geog.leeds.ac.uk |
|
