Page 41 - Contributed Paper Session (CPS) - Volume 5

CPS795 Nestor B.

Stochastic modeling of the impact of climate
change on the variability of daily rainfall in Benin
Nestor BOKOSSA
Univesity of ABomey-Calavi Cotonou, Benin

Abstract
In spite of uncertainties about their width and their variability, the impacts of
the climatic modifications observed as well at the global level as local are
already pointed out in the countries of the sahelo-Saharan zone of Africa like
Benin. The dryness which results from a deficit of the level of precipitations as
well as the distribution of precipitations in time and space constitute the
climatic attributes which make this phenomenon’s degree significant. Our
objective is to model and analyze the level of daily precipitations on the basis
of stochastic model. The proposed model is non homogeneous hidden
Markov model with a special structure that captures the semi-property of
hidden semi-markov model, thus the model allows arbitrary dwell-time
distributions in the states of the Markov chain. Despite the Markov chain is
non homogeneous, we showed that it is semi-regenerative process and
ergodic and identifiable in mild conditions. This model can reflect a stochastic
seasonality of dailys precipitations, and then is able to modelize additional
seasonal variability due to climate evolution. This model delimits both the end
and beginning of rainy seasons, but also through these parameters, the
quantity of precipitation and the regularity of the rainy season from one region
to another. Apply the model to data of Kandi, Parakou, Natitingou, Savé,
Cotonou and Bohicon (six towns of Benin which have synoptic stations) we
prouved the impact of climate change in daily precipitation. And with the
likelihood ratio test, we dected the rupture on the daily precipitation data of
each town.

Keywords
Markov chain; Hidden Markov model; EM-Algorith; Identifiability; Mixture;
breaking; likelihood ratio.

1. Introduction
About its latitude position (between 6 30 and 12 30 of North latitude),
Benin is among countries in which the climate is hot and wet in the
intertropicale zone. The drought that has affected many African countries
south of the Sahara has not spared Benin, especially since the 1970s. The
consequences of this phenomenon are dramatic for the populations:
reduction of water ressources and forest ressources, reduction of livestock,
dam filling up, decrease of agricultural productivity, and brutal reduction of

30 | I S I W S C 2 0 1 9