Monthly extreme rainfall risk envelope graph method development and application in Algeria
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Date
2022
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Université de M'sila
Abstract
Rainfall patterns are bound to change as a result of global warming and climate change impacts.
Rainfall events are dependent on geographic location, geomorphology, coastal area closeness and
general circulation air movements. Accordingly, there are increases and decreases at different
meteorology station time-series records leading to extreme events such as droughts and floods.
This paper suggests a methodology in terms of envelope curves for monthly extreme rainfall event
occurrences at a set of risk levels or return periods that may trigger the extreme occurrences at
meteorology station catchments. Generally, in many regions, individual storm rainfall records are not
available for intensity–duration–frequency (IDF) curve construction. The main purpose of this paper
is, in the absence of individual storm rainfall records, to suggest monthly envelope curves, which
provide a relationship between return period and monthly extreme rainfall values. The first step is to
identify each month extreme rainfall records probability distribution function (PDF) for risk level and
return period calculations. Subsequently, the return period rainfall amount relationships are
presented on double-logarithmic graphs with the best power model as a set of envelope curves.
The applications of these methodologies are implemented for three Hodna drainage basin
meteorology station rainfall records in the northern Algeria. It is concluded that the most extreme
rainfall risky months are June, August and September, which may lead to floods or flash floods in the
study area. A new concept is presented as for the possible extreme value triggering months through
the envelope curves as ‘low’, ‘medium’ and ‘high’ class potentials.
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Keywords
Algeria, envelope, extreme rainfall, probability, return period, risk