Assessing Nonlinear Dynamics and Trends in Precipitation by Ensemble Empirical Mode Decomposition (EEMD) and Fractal Approach in Benin Republic (West Africa)

Médard Noukpo Agbazo,Basile Kounouhewa,Abel Afouda,Eric Alamou,Gabin Koto N’Gobi,Anirban Chakraborti

doi:10.1155/2021/3689397

Abstract

Climate dynamics and trends have significant environmental and socioeconomic impacts; however, in the Benin Republic, they are generally studied with diverse statistical methods ignoring the nonstationarity, nonlinearity, and self-similarity characteristics contained in precipitation time series. This can lead to erroneous conclusions and an unclear understanding of climatic dynamics. Based on daily precipitation data observed in the six synoptic stations of Benin Republic, in the period from 1951 to 2010, we have proposed (i) determining the local trends of precipitations, (ii) investigating precipitation nonlinear dynamics, and (iii) assessing climatic shift in the study period by Ensemble Empirical Mode Decomposition (EEMD) and Multifractal Detrended Fluctuation Analysis (MFDFA) method. To overcome the detrending issue in the standard MFDFA method, the EEMD algorithm is embedded into the MFDFA. The study period is subdivided into three subperiods: 1951–1970, 1971–1990, and 1991–2010. Intrinsic Mode Functions (IMFs) are obtained according to the climatic region in which the stations are located. Results show that precipitation variation is significantly governed by the five first IMFs, in which oscillation periods vary from 1 to 25 days. The trend curves decrease at all the synoptic stations, and their slope values vary accordingly to the subperiods. Referring to the values of the multifractal spectrum parameters, α 0 , and the width of the spectrum w , consistent changes are observed regardless of the subperiods and the concerned stations. The spatial and temporal variability of precipitation indicates that the multifractal properties are good indicators for assessing changes in precipitation dynamics, and the changes in their features could be explained by the global change than by the local climate variation (climatic zones). Despite the observed differences in multifractal spectra properties from the three subperiods, it is not possible to verify the subdivision of 1951–2010 in three subperiods as it is done by previous studies in West Africa. Our findings can be used in the validation of global and regional climate models since a valid model should explain empirically detected scaling properties in observed data.

Highlights

Climate variability and trends have enormous influences on the environment and social development of locations with a growing human population [1, 2]
Precipitation observed in Benin synoptic stations is decomposed into different intrinsic mode functions (IMFs) and residue representing different scales
The IMFs with lower numerical numbers correspond to higher-frequency oscillations, whereas IMFs with higher numerical numbers correspond to lower-frequency oscillations at larger scales

Summary

Introduction

Climate variability and trends have enormous influences on the environment and social development of locations with a growing human population [1, 2]. Climate variability has enormous influences on agricultural and economic development [2]. Precipitations are variable widely collected all over the world and the most affected by climate change and climate variability [6, 7]. They are the main meteorological variables, used for understanding climate dynamics and climate changes [8]. It is not always easy to analyze them because precipitations are highly complex and variable process, exhibiting enormous variability over a wide range of time and space scales [9, 10]

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