|
1. Definition
| Name |
RUNOFF
THRESHOLD (RDI) |
| Brief
definition |
The
amount of storm rainfall that can be absorbed by the soil and
surface before overland flow runoff normally occurs. |
| Unit of measure |
mm |
| Spatial scale |
|
| Temporal scale |
|
2. Position
within the logical framework DPSIR
3. Target and
political pertinence
| Objective |
To
provide a simple measure of the ability of the soil to absorb
storm rainfall. This is used in the PESERA/RDI model, and is
part of the calculation of erosivity. |
| 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. An increased runoff threshold indicates greater infiltration
and less overland flow. Conservation and management methods
are able to modify the runoff threshold directly, through changes
in land use and surface characteristics such as tillage roughness
and terracing. |
| 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 as one of the key soil factors (with erodibility)
that control sediment loss by wash erosion. |
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 plot experiments are analysed month by
month, by graphing storm runoff against storm rainfall, the
runoff threshold is the rainfall above which runoff commonly
occurs. It responds not only to soil composition and structure
but also to the degree of surface crusting and surface depression
storage created by tillage etc. |
| Benchmarks
Indication of the values/ranges of value |
The
runoff threshold varies seasonally, as well as with the course
of vegetation cover development, and rain impact over each season.
Values range from <5mm for a bare crusted surface to 100mm
or more for a deep forest soil. |
| Methods
of measurement |
Can
be measured experimentally in field plots over several years.
Alternatively it may be estimated within the RDI model from
soil available water content (related to texture and structure),
crustability and degree of crust development, and depression
storage due to tillage etc. All but available water content
vary seasonally. |
| 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. |
| Linkages
with other indicators |
Erosivity
(RDI), Erosion risk (RDI) |
5. Evaluation
of data needs and availability
| Data
required to calculate the indicator |
See
methods of measurement. |
| Data
sources |
Necessary
soils data are usually available and accessible to researchers.
Land use and tillage practice may be generalised according to
crop type, or (better) directly observed in the field. |
| 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
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 |
|
