Guy Merlin Guenang

Atmospheric aerosols disturb the Earth's radiative balance through their direct effects (scattering and absorption of solar radiation) and their indirect effects (interaction with clouds). It is now widely recognised that the effect of aerosols on climate change is significant when compared to greenhouse gases. Despite the intensification of studies on this subject, the estimation of the radiative forcing of aerosols and their impact on precipitation remain highly uncertain. This article examines the projected effects of aerosols on the diurnal cycle of precipitation amount and frequency in Central Africa using the latest version of RegCM5 regional climate model from the Abdus Salam International Centre for Theoretical Physics (ICTP), coupled with the Community Land Model version 4.5 as the land surface scheme. RegCM5 is used to dynamically downscale the global climate model that participated in phase 5 of the Coupled Model Intercomparison Project (CMIP5) (HadGEM2‐ES) for both past (1991–2005) and near‐future (2035–2049) periods under the Representative Concentration Pathway (RCP) emission scenarios 2.6, 4.5, and 8.5. For a better analysis of the results, three sub‐regions have been considered based on their land cover and climatic characteristics. Diurnal cycle of precipitation characteristics, as well as the amplitude, and phase of both precipitation amount and frequency, have been investigated. The analyses show that the responses to anthropogenic forcings vary depending on the season and RCP. It emerges that all experiments with RCP forcings, without aerosol effects, show a decrease in both precipitation amount and frequency compared to the historical period. This decrease in precipitation intensifies with the presence of atmospheric aerosols. This suggests that precipitation in Central Africa will be negatively affected by the aerosols present in the surrounding environment. In the presence of aerosols, changes in the amplitudes of precipitation amount and frequency decrease by nearly 5%. In contrast, the changes in phases show both increases or decreases in precipitation across Central Africa and its three sub‐zones with small amounts ( 10 mm/h). The projected changes in the variation of the diurnal cycle of precipitation are nearly identical across all RCP scenarios, which justifies the high similarity obtained between different RCPs for precipitation amount and frequency, except for Zone 1 in DJF, which shows a low similarity.

The objective of this study was to assess household incomes generated by key non-timber forest products in the semiarid Sudano-Sahelian zone of Cameroon. The methodological approach was based on eight focus group discussions (average 15 per focus group discussion) and individual interviews with a total of 116 local communities in the Waza landscape. A total of 12 key non-timber forest products were identified, with Balanites eagyptiaca, Adansonia digitata, Azadirachta indica, Ziziphus mauritania, Tamarindus indica as the most important non-timber forest products in terms of volume and income generated for households. The actors involved in the value chain were the collectors, local traders, intermediate collectors, processors, and traders or retailers. For the most important non-timber forest products, these collections were mainly carried out by women and children, who sell their products independently at home or at the local market. The average production volume varied from 10 to 200 kg.household.year−1 depending on the target non-timber forest product species and the part considered (fruits, seeds, leaves). However, 20-50% of this production was reserved for own consumption and 50-80% for trading. The average annual income generated by these five top non-timber forest products was estimated at 56.48 USD.household.year−1. Baobab fruit, with a maximum income of 260 USD.household.year−1 was found to be a top non-timber forest product that generated maximum household income per year. Traders of non-timber forest products were at three levels, namely house/village, periodic, and urban markets. Buyers were sometimes collectors coming from neighboring countries like Nigeria and Chad. There was an increase in selling prices between house/village and urban markets with an average of +39% (9-100%). Value chain and/or market analyses of non-timber forest products in the Waza landscape provide vital information to help improve production, value addition, or processing, market organization and also increase the contribution of the non-timber forest products to the income of the households involved. Cite this article as :Chimi, C. D., Barnabas, N., N., Merlin, N. G., Serges, O. N., Eugene, C., Kevin, E., Dieudonn., A., A., Princely, N., Roger, K. B. L. P., Lavoine, M. K., Parfait, K. N., Vartant, D. P. S., Kevin, F. T., & Delanot, T. A. (2025). Non-timber forest products in the semi-arid Waza landscape: value chain and contribution to household incomes. Forestist, 75, 0096, doi:10.5152/forestist.2025.24096.

The Sudano-Sahelian region of Cameroon is mainly drained by the Benue, Chari, and Logone rivers; which are very useful for water resources; especially for irrigation, hydropower generation, and navigation. Long-term changes in mean and extreme rainfall events in the region may be of crucial importance in understanding the impacts of climate change. Daily and monthly rainfall data from fifteen climate stations in the study area from 1980 to 2018 and measurements from the Expert Team on Climate Change Detection and Indices (ETCCDI) were estimated using the non-parametric innovative trend analysis (ITA) and the Sen slope estimator. The precipitation concentration index (PCI), the precipitation concentration degree (PCD), and the precipitation concentration period (PCP) were used to explore the spatiotemporal variations in the characteristics of rainfall concentrations. The results showed complex spatial patterns of the annual average PCI values across the Sudano-Sahelian region; which varied from values lower in the south to higher in the far north, which were the characteristic of seasonality and a strong seasonal precipitation distribution throughout the year; respectively. The PCD results revealed that the annual rainy days in a year decreased from the south to the far north. Additionally, the PCP results indicated a slightly later occurrence of precipitation. A significant trend toward more intense–extreme rainfall events was observed in most parts of the study area, but a significant trend toward more humid days was observed in the southeastern part. Trends in dry days significantly increased in the central and southwestern parts of the study area. This could mean that the prevalence of flood and drought risks are higher in the study area. Overall, the increase in annual rainfall could benefit the hydro-power sector, agricultural irrigation, the availability of potable water sources, and food security.

Central African citizens are highly vulnerable to extreme hydroclimatic events due to excess precipitation or to dry spells. This study makes use of CHIRPS precipitation data gridded at 0.05° × 0.05° resolution and extended from 1981 to 2019 to analyze spatial variabilities and trends of six extreme precipitation indices defined by the Expert Team on Climate Change Detection and Indices (ETCCDI) over Cameroon. They are the number of wet days (RR1), the simple daily intensity index (SDII), the annual total precipitation from days greater than the 95th percentile (R95ptot), the maximum number of consecutive wet days (CWD), the maximum number of consecutive dry days (CDD), the number of very heavy rainfall (RR20). The standard precipitation index (SPI) time series were also examined in the five agro-climatic regions of the domain. The pattern of annual precipitation was first checked over the entire domain. We obtain a well-known pattern showing a decreased precipitation northward with the highest values around the Atlantic Ocean coast. The analysis shows that all indices represent patterns approximately similar to that of annual rainfall except CDD where the spatial south-north gradient is reversed. RR20 shows the lowest spatial variability. Trend study of RR1 indicates negative values south of the domain and predominated positive values in the northern part, where CDD, on the contrary, shows a decreased trend. The highest trends are observed in the northernmost area for CWD and around the coast for SDII and R95ptot. SPI time series indicate an alternative dry and wet period and the years between 1990 and 2000 witnessed more annual wet conditions. Such a study is very important in this domain where variabilities of climatic components are very high due to climate change impact and diversified relief. The results can serve as a reference for agricultural activity, hydropower management, civil engineering, planning of economic activities and can contribute to the understanding of the climate system in Cameroon.