Investigating the diurnal cycle of precipitation over Central Africa

AbstractThe present study investigated the reliability of downscaling tool RegCM4.4 to simulate 2002–2006 June–September diurnal cycle precipitation characteristics. Besides their diurnal cycles, the spatial and temporal patterns in precipitation intensity, amount and frequency over Central Africa (CA) are investigated. Diurnal variance, phase and amplitude based on 3‐hourly model simulations are obtained by diurnal harmonics from each 24‐h period. Two statistical measures are used to evaluate model performance: the root mean square error and the index of agreement. The result shows that the RegCM outputs are well simulated compared with reference data in revealing the temporal and spatial patterns of precipitation amount and frequency over the continental area with some systematic wet biases over Cameroon highlands area. Diurnal variability of precipitation frequency and amount are properly well reproduced by the model with an afternoon peak around 1800 LST over entire domain except Atlantic Ocean sub‐region. The model does not properly describe the observed diurnal variation of precipitation intensity over the study area. One of the prominent results is that the pattern of precipitation frequency is quite similar to that of precipitation amount. This strong relationship between these two precipitation characteristics over the entire region of interest suggests that the diurnal precipitation variability is generally determined by how often it rains

Possible influence of the convection schemes in regional climate model RegCM4.6 for climate services over Central Africa

AbstractIn this study we evaluate the reliability of the Regional Climate Model (RegCM4.6) by performing several sensitivity tests at 50 km horizontal resolution using 10 convection schemes or combination of convection schemes. Emphasis on model output is made for the September–October–November 2017–2019 seasonal period. Part of the Central African region, five sub‐regions, was identified. The simulated temperatures are compared to the daily climatology of near‐surface temperature of the European Centre for Medium‐Range Weather Forecasts Reanalysis fifth‐generation and the National Center for Environmental Prediction datasets, while the simulated precipitations are compared to the precipitation of the Global Precipitation Climatology Project and Climate Hazards Group Infrared Precipitation with Stations datasets. In most analyses, the Grell scheme with Arakawa–Schubert closure assumption tends to have the best index of agreement but its spatial distribution shows underestimation of rainfall. Generally, the Emanuel convection scheme is more suitable to represent rainfall and temperature over Central Africa. Compared to our previous study (Komkoua Mbienda et al., International Journal of Climatology, 2017, 37, 328–342), the present study shows that we have to pay attention to the choice of convective scheme when using any version of RegCM4 released for climate study over Central Africa. This choice is strictly related to the RegCM version released, the study years and the season. It is important to note, however, that the results presented are a preliminary study of the response to the selected convection schemes. The analysis uses a limited sample of climate model simulation (three model years for each convection scheme). Follow‐up work, featuring longer duration climate simulations and a full assessment of statistical significance, is therefore required to confirm the robustness of the analysis presented

EVALUATING THE ENVIRONMENTAL IMPACTS OF GARAGES IN CAMEROON USING AN IMPACT MATRIX FRAMEWORK: A CASE STUDY

This study focuses on the assessment of environmental impacts of garages in the Yaoundé II (Yaoundé, Cameroon) subdivision. For this aim, several data from observations and surveys have been used. The surveys were conducted in 49 garages representing 73% of the overall garages counted in March 2015 by the Yaoundé II municipality. The impacts have been identified from the in situ informations regarding the components of garages and existing environmental sensitivities. The impacts on the different environmental components are identified from the matrix method of Leopold. Furthermore, we assessed the extent of impacts with the Martin Fecteau’s Matrix. The various activities of the garages grouped into three domains (mechanical, electrical and sheetmetal) have not only negative impacts on the environment, but also positive impacts. The significant negative impacts are air pollution, degradation of ozone layer, soil pollution and degradation of the health of mechanics. To mitigate these impacts, the proposed measures are summarized in the limitation of gaseous and particulate emissions, the prohibition to dispose wastes on ground, the use of protective equipment and compliance with safety rules. In addition, we also noted the positive impacts including: Increasing of the municipality and state incomes through the payment of various taxes, development of the local economy and opportunities for direct and indirect jobs. To maximize these impacts, it is necessary to improve the working conditions of the mechanics with the assistance of public authorities

Evaluation of Vapor Pressure Estimation Methods for Use in Simulating the Dynamic of Atmospheric Organic Aerosols

The modified Mackay (mM), the Grain-Watson (GW), Myrdal and Yalkovsky (MY), Lee and Kesler (LK), and Ambrose-Walton (AW) methods for estimating vapor pressures () are tested against experimental data for a set of volatile organic compounds (VOC). required to determine gas-particle partitioning of such organic compounds is used as a parameter for simulating the dynamic of atmospheric aerosols. Here, we use the structure-property relationships of VOC to estimate . The accuracy of each of the aforementioned methods is also assessed for each class of compounds (hydrocarbons, monofunctionalized, difunctionalized, and tri- and more functionalized volatile organic species). It is found that the best method for each VOC depends on its functionality

Evaluation of Vapor Pressure Estimation Methods for Use in Simulating the Dynamic of Atmospheric Organic Aerosols

The modified Mackay (mM), the Grain-Watson (GW), Myrdal and Yalkovsky (MY), Lee and Kesler (LK), and Ambrose-Walton (AW) methods for estimating vapor pressures ( vap ) are tested against experimental data for a set of volatile organic compounds (VOC). vap required to determine gas-particle partitioning of such organic compounds is used as a parameter for simulating the dynamic of atmospheric aerosols. Here, we use the structure-property relationships of VOC to estimate vap . The accuracy of each of the aforementioned methods is also assessed for each class of compounds (hydrocarbons, monofunctionalized, difunctionalized, and tri-and more functionalized volatile organic species). It is found that the best method for each VOC depends on its functionality

Enhancement of RegCM4.7‐CLM precipitation and temperature by improved bias correction methods over Central Africa

Abstract Precipitation and temperature projections from Regional Climate Models (RCMs) over Central Africa (CA) are of great importance. However, several studies have already shown that the data from RCMs cannot be directly used for climate impact studies on a local scale because of systematic biases that characterize them. Therefore, RCM simulations must be preprocessed in order to make them more representative of climate at a local scale. The present study focuses on improving temperature and precipitation simulations from the RegCM4.7 RCM over CA. For this purpose, two correction methods are used: The adjusted Linear Scaling and Variance (Va) methods. Corrected and uncorrected precipitation and near‐surface temperature are compared with Climate Hazards group Infrared Precipitation with Stations (CHIRPS) and the fifth generation of ECMWF reanalysis data (ERA5), respectively. Comparison of the performances of both methods was made during various seasons not only over the whole CA region but also over two sub‐domains (Zones 1 and 2) having different characteristics. This was done on the basis of the mean bias and Root Mean Square Error. Results show that the precipitation from RegCM4 is tainted with huge wet biases compared to CHIRPS. Overall, the analysis suggests that the Va method is the most suitable for reducing the biases of RegCM4.7 simulations, particularly for precipitation irrespective of regions or seasons. However, it has been found that both methods fail to improve temperature biases in the Inter‐Tropical Convergence Zone