|
1. Definition
| Name |
RAINFALL |
| Brief
definition |
Mean annual precipitation.
This may occur in many forms and may change from one form
to another during its descent. It may also occur as frozen
water particles such as snow, sleet, or hail.
 |
Recently
cultivated soil subjected to high erosion rates due to
a recent heavy rainstorm event (photo by C. Kosmas) |
|
| Unit
of measure |
mm |
2. Position
within the logical framework DPSIR
3. Target and
political pertinence
| Objective |
Contribution
to the definition and mapping of ESAs and evaluation of the
desertification risk of an area |
| Importance
with respect to desertification |
A fundamental
parameter because it is the primary factor of soil erosion and
because of its influence on the development of vegetation. Together
with the other climate indicators it contributes to forming
a scale of climate quality and consequently to the elaboration
of development strategies compatible with the resources available
in the given area. |
| International
Conventions and agreements |
The
CCD emphasizes that combating desertification must be tackled
within the general framework of actions to promote sustainable
development.
|
| Secondary
objectives of the indicator |
Within
the ESA model is used for investigation of the individual processes
linked to land degradation and desertification. |
4. Methodological
description and basic definitions
| Definitions
and basic concepts |
The scarcity of precipitation,
irregular annual and interannual distribution, extreme events
and out-of season rainy and vegetative periods are the main
climatic factors contributing to land degradation in the semi-arid
and arid zones of the Mediterranean. These give rise to intense
erosion in places where soils is intrinsicly vulnerable. It
is predicted that global climate change will increase the
present extent of vulnerable zones in the Mediterranean.
Rainfall amount and distribution
are the major determinants of biomass production on hilly
lands under Mediterranean conditions. Decreasing rainfall
combined with high rates of evapotranspiration drastically
reduce the soil moisture content available for plant growth.
Reduced biomass production, in turn, directly affects the
organic matter content of the soil and the aggregation and
stability of the surface horizon against erosion.
The high erosion rates
occurring in Mediterranean type areas are attributed to: (a)
to the climatic regime, (b) to the existing generally poor
vegetation cover, and (c) land use management. The extreme
intensity and irregularity of annual precipitation events
is a primary cause of soil erosion in Mediterranean Europe.
During such rainfall events, the impact of raindrops on the
soil surface ("rainsplash") modifies the soil physical
properties. As a consequence, the soil particles are destabilised,
detached and subsequently transported downslope by the running
water. The pressure exerted by the raindrops on the soil causes
strong compaction and consolidation of its surface, resulting
in an impermeable soil crust that inhibits infiltration and
increases runoff.
Erosion data collected
in various sites along the Mediterranean region shows that
annual rainfall of 280-300 mm has a crucial effect in increasing
run-off (see figure). Generally, there is a tendency for increasing
run-off and sediment loss with decreasing rainfall in hilly
Mediterranean shrublands, especially in the region where rainfall
is greater than 300 mm/year. Below the 280 mm annual rainfall
limit, run-off and sediment loss decreases with decreasing
rainfall.
 |
Relationships
between run-off and annual precipitation measured at four
Mediterranean sites under shrubland (Kosmas et al., 1997). |
|
| Benchmarks
Indication of the values/ranges of value |
- >650 mm,
- 280-650 mm,
- <280 mm
|
| Methods
of measurement |
Rainfall
is easy to quantify with a pluviomenter and pluviograph. |
| Limits
of the indicator |
The
quality of the indicator depends n the number and distribution
of rain monitoring stations over the area. Since rainfall it
is very variable in time and space, to obtain mean monthly,
seasonal and annual values in a determined area, the stations
have to be evenly distributed across the country. |
| Linkages
with other indicators |
Aridity
index (1), Aridity index
(2), Vegetation cover,
Water availability, Fire
risk, Rainfall seasonality,
Soil salinity index |
5. Evaluation
of data needs and availability
| Data
required to calculate the indicator |
Data
required are annual rainfall statistics available from the various
stations situated in the area under study, on the basis of series
spanning at least a period of 30 years. |
| Data sources |
Necessary data
are usually available and accessible and the cost/benefit ratio
is reasonable. |
| Availability
of data from national and international sources |
Data
can be obtained from various regional, national or international
institutions involved in the collection and elaboration of such
data. |
6. Institutions
that have participated in developing the indicator
| Main institutions
responsible |
Agricultural
University of Athens |
| Other contributing
organizations |
Universities
of Lisbon, Murcia, Basilicata, Amsterdam, Leeds
|
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 p. |
| Other references |
Kosmas, C., Danalatos,
N., Cammeraat, L.H., Chabart, M., Diamantopoulos, J., Farand,
R., Gutierrez, L., Jacob, A., Marques, H., Martinez-Fernandez,
J., Mizara, A., Moustakas, N., Nicolau, J.M. Oliveros, C.,
Pinna, G., Puddu, R., Puigdefabregas, J., Roxo, M., Simao,
A., Stamou, G., Tomasi, N., Usai, D., and Vacca, A., 1997.
The effect of land use on runoff and soil erosion rates under
Mediterranean conditions. Catena, 29:45-59.
Lavee, H., Imeson, A.C.,
Parientes, S., and Benjamini, Y., 1991. The response of soils
to simulated rainfall along a climatological gradient in the
arid and semi-arid region. Catena Supplement, 19:19-37.
|
| Contacts Name
and address |
Agricultural University
of Athens, Laboratory of Soils and Agricultural Chemistry,
Iera Odos 75, Athens 11855, Greece
Dr Constantinos Kosmas
email: lsos2kok@aua.gr
|
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