Abstract
This study analyzed the long-term memory (LTM) in precipitation over Bénin synoptic stations from 1951 to 2010 using the detrended fluctuation analysis (DFA) method. Results reveal the existence of positive long-term memory characteristic in rainfall field. DFA exponent values are different regarding the concerned synoptic stations, reflecting the effect of geographical position and climate on the LTM. These values were related to the type of climate. The best DFA1-4 method depends on the geographical position of the studied station. However, DFA2 is generally the best in terms of spatial average from DFA1 to DFA4. In Bénin synoptic stations, except the Parakou station, the long-term temporal correlations are systematically the source of multifractality in rainfall. Except Natitingou, the strength of long-term memory characteristic decreases each twenty years in the study period. Considering the fractal approach, our results show that the subperiod 1991–2010 is not really a transition period as shown before. Thus, the drought is prolonging until 2010. So, fractal theory reveals more Bénin climatic characteristics.
Highlights
According to several reports, such as those of the United Nations Framework Convention on Climate Change [1], the International Panel of Climate Change (IPCC) [2], several documents produced by the World Bank [3], and the Climate Change and Urban Vulnerability in Africa (CLUVA) project [4], Africa is considered as a continent vulnerable to climate change
According to Hall [16] and Varotsos and Efstathiou [17], the relationship between the detrended fluctuation analysis (DFA) exponent and the classic Hurst exponent H can be expressed as (i) for fractional Gaussian noise, H is equal to DFA exponent and (ii) for fractional Brownian motions, H is equal to DFA exponent 1
Whatever the DFAm method, h values present spatial variation, there is a South-North gradient, (c) over all synoptic stations, h values are systematically between 0.5 and 1, this means that there exists positive long-term memory characteristic in the rainfall field, and (d) among synoptic stations, the highest and lowest values of h are, respectively, obtained at Cotonou and Bohicon stations, indicating the existence of strong and weak long-term memory characteristics in Cotonou and Bohicon
Summary
According to several reports, such as those of the United Nations Framework Convention on Climate Change [1], the International Panel of Climate Change (IPCC) [2], several documents produced by the World Bank [3], and the Climate Change and Urban Vulnerability in Africa (CLUVA) project [4], Africa is considered as a continent vulnerable to climate change. Kantelhardt et al [9] have studied, by the detrended fluctuation analysis (DFA) method, the LTM characteristics of precipitation records in Europe, Asia, and America. According to Taqqu et al [13] and Kantelhardt et al [9], the DFA method permits to Advances in Meteorology estimate the Hurst exponent H. It is important to remind the distinction of the classic Hurst and the DFA exponent as announced in Taqqu et al [13], Movahed et al [14, 15], and more recently as clarified by Hall [16] and Varotsos and Efstathiou [17]. One can be sure of the universality of the correlations in climatological time series but its DFA exponents can be related to local patterns
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