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tub), but the water has no shear strength, reducing signifi cantly the forces of
friction and cohesion that resist slipping. On the other hand, the movement
of water in the soil causes percolation, which changes the balance of the
slope and leads to landslides.
If the slope has vegetation, these landslides are less but if the slope
has been cleared for settlements even less intense rainfall events cause
the imbalance triggering landslides. Based on this, the inhabitation of
slopes should be avoided and already inhabited slopes should be vacated,
restoring the original topography and natural vegetation coverage. In many
situations, however, it is not possible to evacuate the slopes, it is necessary
to urbanize and consolidate existing occupations.
This chapter deals with a criterion for classifi cation and ranking of
risks of landslides slopes, part of the actions necessary to urbanization and
consolidation of the occupied slopes.
Global Change, Extreme Weather and Prevention
Recent research by the Brazilian Agricultural Research Corporation
(EMBRAPA) in conjunction with the University of Campinas—SP
(UNICAMP), where they studied 78 meteorological stations all over Brazil,
that showed an increase in average annual temperature of 1.5°C since 1968
to date. As a result of this increase in temperature, there was a signifi cant
increase in the intensity of rainfall and there has been an increase in the
amount of annual precipitation. There has been a poor temporal and spatial
distribution for rainfall events with prolonged drought seasons and intense
and prolonged rainfall events during rainy season. This leads to increase
in the occurence of landslides in the urban areas.
In 1991 UNDRO—United Nations Disaster Relief Organization proposed
a model to counter natural disasters based on Prevention and Preparation.
Prevention activities are related to technical and scientifi c studies
that can assess the likelihood of occurrence and magnitude of a natural
disaster, establishing mechanisms to prevent loss of not only lives, but
also to minimize property losses. The preparation actions are linked to the
logistical nature of the confrontation of emergency situations and care of
affected populations, and is usually assignments of civil defense agents
(Alheiros, M.M. in UFPE 2008). These aspects are very important, but not
discussed in this chapter.
Occupation of the Hills and Mapping Geotechnical Risks
In Brazil, as well as in other countries urbanization has been totally
unplanned and has usually marginalized poor people. It has also led to
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