Geography Reference
In-Depth Information
by a number of geomorphologic characteristics, which distinguishes them from
neighbouring areas. The localized and moderate hills and flat plains are the classes with the
highest representation. Allied to information on soil type and vegetation cover, the former,
appears to have a moderate to high erosion risk and the latter might have a low to moderate
risk. However, in future research, it is intended to create a more accurate map of erosion
risks, by matching the satellite images, climatic data, mapping of land use, geological and
pedological features in an appropriate scale. Moreover, methodology used in this study for
landform mapping, can also be validated by elaborating a descriptive mapping of a sample
area, based in photo interpretation and field observations. The aerial photography, with 60%
overlap, allows the creation of stereoscopic pairs which facilitate the characterization of the
terrain. Fieldwork will also be useful for add and/or confirm the information obtained by
stereo restitution. Comparison of the pixels in each unit of land allows validating the model.
3. Mapping of rainfall erosion in Serra de Grândola
3.1. Introduction
Erosion is a global scale threat to sustainability and productive capacity of the soil (
e.g.
,
Yang
et al.
, 2003; Feng
et al.
, 2010). It is estimated that about 10 million hectares of farmland
are lost annually in the world due to soil erosion (Yang
et al.
, 2003; Pimentel, 2006).
Climate change may have a great influence in soil erosion (Pruski and Nearing, 2002). Changes
in the erosive power of rainfall can be hazardous in terms of soil erosion (Favis-Mortlock and
Savabi, 1996; Williams
et al.
, 1996; Favis-Mortlock and Guerra, 1999; Pruski and Nearing, 2002).
Erosion, the most common type of soil degradation, should be considered as the main
symptom of desertification. Since the first half of the XX Century numerous studies have
been carried out and gave a strong contribution to the knowledge on the mechanical
processes leading to erosion and how these processes interact in the environment. However,
studies on how social, economic, political and institutional factors are affected by erosion,
have been developed only during the last decades.
According to the digital Soil Map of the World (FAO, 1989) and a climate database Eswaran
et al.
(2001) the vulnerability to desertification of the Mediterranean area countries, it is
considered that more than 600,000 km
2
of the Mediterranean basin are at risk of
desertification. Project DesertWatch, presented at the 10
th
Conference of the Parties to the
United Nations Convention to Combat Desertification, states that the 33% of the Portuguese
territory is at risk of desertification, being the Alentejo the most affected area.
The main objective of this work is the development of a GIS to determine the risk of erosion
in Serra de Grândola (Alentejo, Portugal).
3.2. Study area
The study area is delimited by the UTM coordinates: Zone 29S, M
min
=512,930.44 m,
P
min
=4,205,893.13 m, M
máx
=540,965.44 m, P
máx
=4,230,328.13 m. Its area, with 675 km
2
, includes
