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Past and future annual droughts in the five agro-ecological zones of Cameroon

Guenang G. M., Komkoua Mbienda A. J., Kaissassou S., Vondou Derbetini A., Gounmene M., Tanessong R. S., Yepdo Z., Njinkeu S. W.

Acta Geophysica

2024

Vol. 72, no. 3

2127--2140

This paper studies the past and future annual droughts in the five agro-ecological zones (AEZs) of Cameroon. Station data and model outputs from the Coupled Model Intercomparison Project Phase 5 were used to compute areal datasets for each AEZ. Six statistical metrics and compromise programming method were used to evaluate and rank the models, respectively. The top three models were used to build multi-model ensemble (MME) and deduce bias-corrected MME data. They were then used to compute the Standardized Precipitation Index (SPI) used as drought indicator. As a result, the performance of the models depends on the AEZ and decreases with the increase in drought intensity. The 1980s was the most marked by severe-extreme droughts and a significant increase in drought intensity was observed in the entire domain during the past period, the years 1974, 1985 and 1988 showing the highest drought intensities. The MME tends to overestimate and underestimate the frequencies and the magnitude of these events, respectively. Bias-corrected MME data improve the results in most cases. As for the period 2071-2099, all the AEZs are likely to experience severe-extreme droughts which are expected to be more frequent before 2083 in the North (AEZs 1 and 2) and after this year in the South (AEZs 3, 4 and 5). It is also expected a slight increasing trend of the mean spatial SPIs showing a slight decrease in drought intensity. The RCPs 8.5 and 2.6 project the lowest and the highest decrease in drought intensity, respectively, while the RCP4.5 shows an average decrease. This study highlights future periods and areas at potential risk of severe-extreme droughts and can guide decision-makers in mitigation and adaptation measures.

An investigation into the role of synoptic conditions on Central African precipitation variability

Zebaze Sinclaire, Pathak Raju, Komkoua Mbienda A. J., Pokam Mba Wilfried, Salunke Popat, Anand Abhishek, Vondou Derbetini Appolinaire, Lenouo André, Mishra Saroj Kanta

Acta Geophysica

2022

Vol. 70, no 2

943--962

The synoptic precipitation variability over Central Africa (CA) in the March-to-May (MAM) and September-to-November (SON) seasons is investigated in this study. The composite analysis is used to highlight the evolution of synoptic precipitation, related convection, and dynamic fields. Composite analysis findings show that synoptic precipitation anomalies increase/ fade with an increase/decrease in convection, with the largest amplitude over 5° S–10° N and 2.5–20° E in MAM and 5° N–7.5° N and 5–15° E in SON. Precipitation anomalies and convection associated with the synoptic variability progress eastward preceded (followed) by eastward (westward) low-level wind. This synoptic sequence is associated with a downward motion and an inflow, indicating the storm’s presence, which contributes significantly to precipitation initiation over CA. The empirical orthogonal function for precipitation during the SON season is lower than that observed during the MAM season in the context of the size and spatial pattern. During these precipitation occurrences, the zonal moisture component contributes the most to the moisture initiation over the region. The findings of this study show that the observed convergence/ divergence position remains unchanged in intensity irrespective of the positive/negative precipitation events. Overall, the synoptic-scale conditions in MAM contribute around 58% of the total variability in precipitation.