Volume 13 Number 7 (July )

Intensification of Climate Extremes in the Sudanian Zone of Benin: Diagnosis Based on ETCCDI Indices Intensification des Extrêmes Climatiques Dans le Domaine Soudanien au Bénin: Diagnostic Basé Sur les Indices Etccdi

ynoptic stations over the period 1981-2025. Extreme rainfall and temperature events were determined using XLSTAT 2018 for the computation of 20 ETCCDI indices derived from Rclimdex 2.0, coupled with the Mann-Kendall trend test. A marked spatial variability in annual precipitation (PRCPTOT) was evidenced, with totals ranging from 750 to 2,000 mm yr-1; the highest accumulations were observed in the southern sector (Savalou, Glazoue, Ouesse), while the lowest values (746-913 mm) were recorded in the extreme north (Karimama and Malanville). Extreme indices further corroborate this intensification: RX5day reached 90-110 mm, R99p exceeded 115 mm, R95p ranged between 60 and 100 mm, while R1day surpassed 35 mm day-1 and the Simple Daily Intensity Index (SDII) exceeded 9 mm day-1 in the southeastern part. Analysis of temperature extremes at Parakou indicated significant increases in tropical nights (TR = 2.15; p = 0.03) and warm nights (TN90p = 4.13; p < 0.001), alongside rising extreme maximum values (TXX = 2.18; p = 0.03; TNX = 2.11; p = 0.03). Furthermore, cold spell duration indices (CSDI) exhibited a significant decline (Z = -3.75; p < 0.001). In contrast, at Kandi, the trends were more moderate, with an increase in warm nights (TN90p = 2.86; p = 0.004) and a significant decrease in extreme minima (TNN = -2.65; p = 0.008). These climatic and bioclimatic trends underscore the vulnerability of human health and point toward the need for sustainable, resilient adaptation strategies for local populations. Resume-L'analyse des indices climatiques ETCCDI au niveau des stations du domaine soudanien au Benin a montre l'intensification des extremes pluviometriques et thermometriques. Les donnees utilisees sont les releves de pluies et de temperatures (maximales et minimales) journalieres de 22 postes pluviometriques et de deux stations synoptiques sur la periode de 1981-2025. Les extremes de pluies et de temperature ont ete determines a l'aide du logiciel XLSTAT 2018 pour le calcul de 20 indices de l'ETCCDI a partir de Rclimdex 2.0 et du test de tendance de Mann-Kendall. Une forte variabilite spatiale des precipitations annuelles (PRCPTOT) est mise en evidence, avec des cumuls de 750 a 2 000 mm/an, les plus eleves observes au sud (Savalou, Glazoue, Ouesse) et de 746-913 mm, les plus faibles a l'extreme nord (Karimama et Malanville). Les indices extremes confirment cette intensification : RX5day atteint 90-110 mm, R99p depasse 115 mm, R95p varie entre 60 et 100 mm, tandis que R1day depasse 35 mm/jour et que le SDII atteint plus de 9 mm/jour au sud-est. L'analyse des extremes de temperature a montre qu'a Parakou, les indices revelent une hausse significative des nuits tropicales (TR = 2,15 ; p = 0,03) et des nuits chaudes (TN90p = 4,13 ; p < 0,001), accompagnee d'une augmentation des valeurs maximales extremes (TXX = 2,18 ; p = 0,03 ; TNX = 2,11 ; p = 0,03). En outre, les vagues de froid (CSDI) ont baisse significativement (Z = -3,75 ; p < 0,001). Par contre, a Kandi, l'evolution est plus moderee avec la hausse des nuits chaudes (TN90p = 2,86 ; p = 0,004) et la baisse significative des minima extremes (TNN = -2,65 ; p = 0,008). Cette tendance climatique et bioclimatique renseigne sur la vulnerabilite de la sante humaine et oriente vers les perspectives de strategies resilientes durables des populations.

Experimental Assessment of Compact Holographic Lens Imaging Systems for In-Plane Displacement Measurements

Arasad Ali Khan

Coherent imaging systems using holographic lenses have demonstrated significant potential in speckle metrology for diffraction-limited imaging performance free of all monochromatic aberrations. In this work, a compact four-hololens system has been investigated for in-plane displacement measurement and compared with two-hololens and double-aperture two-hololens imaging systems. Experimental results obtained using holographic lenses with a typical f-number 7.1 demonstrate that by employing an appropriate recording and reconstruction geometry for holographic lenses, the four-hololens configuration provides higher measurement sensitivity, reducing the minimum measurable in-plane displacement than the existing two-hololens systems.

Experimental Assessment of a Compact Four-Hololens Imaging System Using Holographic Lenses from Glass and Emulsion Sides for In-Plane Displacement Measurement

Arasad Ali Khan

To achieve diffraction-limited imaging over extended objects with negligible monochromatic aberrations, coherent imaging systems based on two identical holographic lenses in a conjugate arrangement have gained considerable attention in speckle metrology. However, the measurement sensitivity, defined as the minimum measurable in-plane displacement of a two-hololens system, is limited by the f-number of the holographic lenses. To overcome the dependency of measurement sensitivity on f-number of holographic lenses, the use of a double-aperture four-hololens system is investigated. Holographic lenses are employed from both emulsion and glass sides in the four-hololens system. Experiments were performed using holographic lenses recorded with a typical f-number of 7.1 and inter-beam recording angles of 11° and 18° between the plane and spherical recording beams. The experimental results demonstrate that holographic lenses recorded with a larger inter-beam recording angle provide high measurement sensitivity, while the use of holographic lenses from emulsion and glass sides has no significant effect on the in-plane displacement measurement. Furthermore, employing holographic lenses on both the emulsion and glass sides facilitates the easy alignment of the holographic lenses within the four-hololens system.